I don’t know if you’ve checked, but I did noticed some oil in the manifold. You might have to replace the PCV valve. Happened to my friends car. During stops, it would hesitate and die sometime. Change the PCV valve and fixed it.

I am a ASE certified diagnostic technician who has decades of experience. This is a running list of things that popped into my head of what possible causes might be... Reminds me of the 5 cyl they put in the Colorado and Trail Blazer, Those intake plenums love to crack and leak. A way to help determine if there is an intake leak is to hook up the scanner and observe the short term trim data and see if is trending to a negative trim, also observe the long term data to see if it is also in negative trim. Another observation is O2S1 trending lean. [hanging closer to 200mv] A smoke machine can be helpful in identifying intake leaks, feed the brake booster line with the smoke. The valve cover bolts are shoulder bolts and torque is not really important. They tighten to the shoulder and dictate max pressure on the seals, you just want to be sure they can't vibrate loose and of course don't snap them off into the head when tightening, use common sense when tightening. Confirm plugs aren't oil fouled from previous valve cover gasket well seal leaks. [you should have done that while the cover was off and just went ahead and put new plugs in as well. A/C Delco likely platinum. Platinum are usually good for a 100k] Clean the mass air flow [MAF] if it has one and if it does the scanner should reveal between 5-6gpm at an idle for that size motor. Confirm the actual gpm spec, it is also a high suspect for rough idle. O2S1 and trims can also reveal leaking injector(s) via a rich reading or positive trim. Check the misfire count data if available [not all models have that feature] to help identify random misfire or cyl specific misfire, typically if the misfire exceed a threshold it will set and code and the MIL light on. If misfire is more on a specific cyl, then swap the coil pack with another cyl and see if the misfires move with the coil pack to determine if you have a faulty coil pack. [COP] Check the motor mounts, hydraulic ones live to leak out the oil and then transmit engine vibration the chassis giving a feeling of rough idle. Most engines have a small amount of random cyl misfires or aren't perfectly balanced although a 6 cyl crank is automatically naturally balanced.

I also had a GMC Envoy for about 12 years 300k miles. I ran into the same issue. It started when I cleaned the throttle body. It ran the sa.e way afterward. So I replaced the throttle body. Which wasn't expensive at all. And the problem was cured. Hope that may help you. I loved my Envoy. I just didn't need it anymore. Great channel keep it up.

My rough idle was do to carbon build up on the throttle body blade

The ticking could be the timing belt tensioner. And if the chain is off a bit that could be the rough idle. They are known to stretch. Replaced mine this last summer

Wow! My vehicle has 446,000 miles on the odometer. Believe it or not, I bought it with only 11 miles, back in 1996. The engine sounds wonderful.

I had similar issues with a 6.0l. I ended up replacing the throttle body. But the issue was the throttle position sensor. Good luck.

If ur thinking of a vacuum leak maybe use a smoke machine I know that kinda a special tool but maybe have a buddy or someone and smoke the intake system and if it is leaking due to looping idle. Maybe use a scan tool and also look at fuel trims and see if it running rich or lean? Just shooting a idea out there

Thank you bruv. Your transparency is appreciated.

Over the years I have replaced 10-12 intake manifolds on the 4.2 and 3.7 due to cracks forming in the seam across the back of the intake. They suck in un-metered air and cause roughness. Can usually see it in the fuel trims. I made a couple plates to bolt on to seal off the manifold and use a smoke machine to check for leaks,

On my Izusu asscender same car, fuel pressure. Wasn’t the fuel pump it was the connection to the relay under the relay box. Fixed the connection ran great. Best of luck

Man, your editing quality is great Jimmy. 96 K2500

First thing I do when diagnosing an engine noise is release tension on the accessories belt and run the motor for a few seconds. If the sound goes away, it’s an accessory. Troubleshoot alternator, power steering, AC clutch and water pump as necessary.

Trailblazer and Envoy intake manifold, bolts, back out overtime with hot and cold cycles. I chased a intake leak forever until I found a couple of the bolts in the back were loose.also make sure you clean the throttlebody. These trucks are very sensitive to that.

Depending on your scan tool, look at mode 6 data to see misfire data. There are videos about it.

If you suspect a manifold gasket leak, before you dismantle, with engine idling, spray the gasket areas with carb cleaner. If the engine slows down, you have a leak. When you have a weird sound, you can isolate it well with a stethoscope with a long narrow tube on it, made for that purpose. It's low tech but you can narrow down where the sound is coming from. As for the AC Delco alternator, I bought a NEW one for my '03, ZR2, not rebuilt, from Rock Auto and got a great deal on it. The original lasted 125k. The new AC Delco alt, started making bearing noise after about 7k miles. I'm still running it, but yes, Delco junk. But was able to isolate the noise to the alt with the stethoscope probe.

Sir, you seem like the perfect person to speak on an experience I had with engine noise. I had a loud engine tick that cane suddenly, and I was 100% sure it was a rod bearing because it was coming from the bottom and was much louder under the van whether the hood was open or shut. I bought new bearings, sandpapers, and other stuff. After pulling the pan, I didn't find anything loose. On a hail mary, I opened the top of the engine because these vans are known for ticking lifters, so I replaced any that i felt were too loose. Problem solved. Relief set in x 1000. But, the wierd thing is how loud the top-end tick was u derneath the van. Anyone hearing that wouldn't have said it was a lifter unless they had that exact problem before.

love the content. keep up the great work

Though I’ve never played with the inline engines.I’ve had similar issues with a caddy 3.6 and a few 4.8,5.3,6.0’s with a purge valve not sealing or operating properly. The old test was to unhook it take off and see if you blow thru it. If you could it would be labeled as bad. The fancy way is with a scanner and watch fuel tank pressure as you use a scanner to open and close the valve. Best of luck on finding the issue and always enjoy your videos! Cheers!

First time viewer, aircraft mechanic and I was raised on a farm and worked on tractors and vehicles my whole life. I would check the fuel pressure at your fuel line you disconnected, a weak fuel pump can cause idle issues and stalling, stumbling, weak aceleration, etc. like the things that you mentioned. Fuel pump is probably inside the fuel tank on the tank quantity sending unit.

Don't worry about the critics, if it doesn't fix it you still got a video showing how to do a task on this truck. Helps some who's wants to know how to do this task

Did you happen to check spark plug tubes for oil? I need to do this to my 07 Trailblazer. Not looking forward to it.

Nice job Jimmy.Have you checked your fuel pressure?

My 2002 2500hd with the 6.0 wouldn't stay running when cold once it was warm it did fine. I replaced the factory intake manifold gasket with Felpro. Been working flawlessly! My understanding is that GM factory intakes gaskets was junk and they changed the material later. They shrink when they are cold, once warm air flows the expand back to where need to be. I think i read to use flepro.

The last time I was working on one of these it said a lean code and the problem was the intake manifold bolts had just simply loosened up but the shop manager and the shop owner basically did not want me to tightening them down and giving them back he basically told me we needed to sell them a new intake manifold gasket I'm glad I don't work on cars anymore the fraud that you are expected to take part in just to pay the rent is pretty ridiculous

Great tutorial on how to change the intake and valve cover gaskets, not a total loss! You resealed a problem area and now oil will not fill up the sparkplug wells. You will find the problem, Jimmy. You got this!

Thanks for being you, as always educational.

Jimmy could it your throttle body sensor that’s causing the ruff Idle .

As you saw the intake valves were dirty. This is a problem when they went to direct injection. In the past, fuel was sprayed behind the valves. This kept them clean by using the fuel as a solvent. Gm sells a solvent and a brush that you remove the intake manifold and spray/scrub the intake valves. Depending on how you drive this vehicle, this should last many miles. But I’ve seen this last as little as 6000 miles. This is dependent on your driving conditions. Good vid and at least you got that noise fixed.

Your alternator "knock" was probably being picked up by the knock sensor, causing the ecu to adjust ignition timing. The intake gasket may or may not have been faulty also.

Did you change the throttle position sensor? Sounds like a possible TPS to me and should be a pretty quick change

Is your fuel filter located inside the tank with fuel pump or is it outside the tank, my Pontiac torrent has that idling problem too and my fuel filter is inside the tank

When I had similar idle issues I cleaned the throttle body and that solved it. I only had 50k miles on it but there was already carbon buildup on the throttle body.

Maybe the mass air flow sensor? Similar issue on older Chevy's I have worked on in the past and it was the MAF. Going to do my valve cover gasket soon as well for the same reason of oil in some of the spark plug holes.

Intake leaks cant lean your engine out and tear an engine up. Ive had valve cover gaskets leak and KILL my alternator a few times in my time. Good video brother.

Do a cylinder balance test and like previously recommended, look at misfire data. If they dont prove out, you may have a dirty injector.

Do you recomend Amazon for the new parts?

Great video

Does this car have a gas tank vapor absorber? I had a similar story, I used smoke to find leaks, they were there, but they only affected the corrections that I looked through the ELM scanner. The main reason turned out to be a stuck adsorber valve, which did not close by about 5-10%. And also, everything is fine, but the idle is not smooth. Replacing the valve solved the issue.

Hi Jimmy, out of curiosity. Have you replaced the engine coolant temp sensor by chance? The 4.2 relies heavily on every one of its sensors to run correctly, and a flaky sensor can definitely cause it. If possible, I would do a fuel pressure test to be on the safe side. The factory rated pressure specification is 50-57 PSI, anything less is typically a fuel pump. If the fuel pump needs to be replaced, stick to BOSCH (they provide the OEM fuel pumps for the 4.2, and 5.3 Envoy/TB.) I would give the MAP sensor a good cleaning (or replace it, its a relatively cheap part). Since the 4.2 was never equipped with a PCV system, all the oil/blow-by just gets sent back through hence why the intake manifold had that gunk around the ports. The MAP sensor is located at the top of the manifold next to the throttle body. The rough idle/stalling at a stop were usually linked to the throttle body being dirty, but since you've cleaned it you MAY need to do a relearn (if you haven't). The procedure for the 4.2 is; Disconnect the negative cable Leave battery disconnected for 30-40 minutes Turn key to ON, do not start the engine or touch the gas pedal. You may/may not hear the TB actuating during this time. After leaving the key to the ON position for 5 minutes, do not turn the key to the off position, instead start her up and let her idle for 10-15 minutes. Drive around to get it to operating temp, and see if that makes a difference. Otherwise, I would suggest getting a test done on the fuel injectors.

Recommend checking coil packs (ohm and Meg), fuel filter, check readings for MAP, MAF, and TPS, look for cracked vacuum lines. These are some items that I have chased in the past. Don't just throw parts at it, try to verify bad parts. Great work on finding the bad bearing in the alternator. I've had that one before too, lol.

Very enjoyable and interesting, thanks 20:25

So what about the third gen Sienna? How are you supposed to change the spark plugs without removing the intake manifold?

I had the alternator for my 97 Olds 88 go out with bad bearings. It was an upgraded Mechman alternator and the bearing towards the rear totally blew apart and was wobbling around. Thankfully I could limp home and had power if I let the engine idle but as soon as I gave it gas it would moan really bad and drop the voltage.

I'm not good w/sensors but could the knock sensor be picking up the alt noise?

I have an 06 trailblazer that im going to continue doing lots of work man, thank youuu!!!

Some of these have a metal intake alternative. My Buick has a later style metal alternative I’ll be switching to when I go to do my lower intake gaskets next weekend. Got the adapter plate, & changing the lower intake elbow orings or just new elbows cuz it already has the metal ones. Try some fuel cleaner next on it, & see if that helps.

Haha, your thumbnail caught my attention, I have the 2.9 version of the Vortec inline with the same manifold and everything really, I actually have a rough idle on my truck, it's kinda on and off but not nuts, maybe I'll take a look at these gaskets now, could be the culprit, cheers!

That flattening is called compression set, all elastomeric materials will take a set after prolonged compression an heat adds to this issue, elastomers are really highly viscous liquids, its just a matter of time before this happens

Excellent video Jimmy :) you can try a grey bottle of STP Total Treatment fuel injection and carb cleaner in fuel tank too see happens if no difference try 89 with 5 % Ethonal or 90 plus higher with no Ethonal % see happens to try !

Smoke the intake and valve cover etc. This is a very good way too either find a leak or eliminate them from the diagnosis. You also could have something affecting your fuel system, you really need a scan tool to check that , and many other things. You don't have to have a cel for something to be wrong. Hope this helps.

Check the valve clearances. differences in valve lash greatly affects valve overlap. If I pull a valve cover for any reason, I do that, just to look for obvious problems. Injection systems are very accurate delivering the same dose of fuel to each cylinder. It's extremely important, that the volumetric efficiency of each cylinder is exactly the same. If some cylinders are rich, and others lean, the O2 sensor will pick a "happy medium" causing a power imbalance, and, higher emission figures. you can get some clues, by pulling and reading the sparkplugs. another possible vacuum leak may be the vacuum brake booster, or, the heater vent controls. Remove those lines from the manifold, plug them, and see if the engine runs any better. I don't understand what you mean by "never touch your factory intake manifold gaskets".

Have you tried a compression check?

thank you

Suggestions. Take the coil packs back out and use some dielectric on the plug ends and clean the oil out of the plug wells.

Mass air flow meter it is possible to clean them with electric contact cleaner spray on heated wire with it removed form car put in plastic bag so the cleaner doesn’t evaporate and give it a good spray . Then let air dry 👍

Thanks!

i would check air fuel pids cause if there was a vacume leak then u will see it in the fuel trims

Did you reset the pcm after taking throttle body off.? I didnt do that on mine at first and it was idling really rough until i did

You need a good scanner to check your computer for error codes. After what you have done to that car i would be checking the fuel pressure. How long is it since you changed the fuel filter?

Does it have fuel filter that is not in the tank? If so I would change the fuel filter. What brand of spark plugs are in it? I would put the exact plug in that it left the factory with. Should tell you in the owners manual. So it was doing this with the old coils and you replaced the old coils with new coils and it still does it? Do you get a random cylinder mis fire code or are you getting a specific cyclinder misfire code? What is the live stream data saying?

One thing that comes to mind is PCV system and/or something like the oil cap gasket or dip stick tube seals.

Great video. I'm not exactly sure where you're at with your rough idle situation with your envoy. that being said, have you cleaned your map sensor Manifold, absolute pressure sensor with the correct cleaner not to use brake cleaning or carburetter cleaner because it doesn't dry quick enough you must use intake manifold cleaner. This could give your engine, a false reading giving it a rough idol. I'm assuming you probably already changed the spark plugs and they were of the correct type and gap even though they likely came already pre-gapped it's good practice to check to be sure. Have you taken a look at your fuel filter or changed it as well your air filter I'm assuming you've changed because it's best practice and less expensive that way to start with unless you have a fancy scan tool you can hook up to check your engine live data. Another possibility could be your fuel injectors or fuel system could be dirty sometimes I can of Bernie B12 or something similar to that typically would help clean up clogged or dirty, feeling injectors as well as your intake valves. There's excessive carbon on the tops of your piston that would also affect the performance of the engine, giving it less for the fuel and air mixture to ignite. Did the rough idol start after you cleaned the throttle body assembly. Some vehicles require a relearn procedure due to the increased volume of air Once I thought the bodies cleaned to look like new. Do you have any exhaust leaks? if so, that will affect your engine performance as well if there's an exhaust leak, then the O2 sensors downstream pick up a false reading, which would then prompt the engines ECU to add or decrease fuel. That could be checked using a cheap scanner off Amazon by checking the fuel trim both short term and long-term. Given that your engine has low mileage, it should be close to zero. Being perfect meaning, the fuel injectors are injecting the exact amount needed for the engine. I'm watching this video now, so I'm not sure if you've already fixed the problem. Keep up the educational and entertaining videos on how to.?

90 chevy truck butterfly in exhaust was rattling once in a while , which sensors picked up as engine knock adjusting fuel causing rough engine running, swapped about a hundred things before one thing standing on passenger side it rattled and engine acted up.

Had a rough idle on my 09 impala. Needed work on the tps (throttle position sensor) and I also cleaned the idle air intake and put in all new air filter. This solved the issue, but it’s also worth noting that I did put in a new injector wiring harness. This was at 235,000 and the engine previously was running on all factory parts (replaced the serpentine belt at 240k and spark plugs and plug wires a little before 235k). I reused the original intake manifold gaskets and it’s been running like a top aside from a small evap leak that’s probably a gasket that I should’ve replaced when I did the wiring harness

A lot of speculation as to your issue. My recommendation would be to buy a scanner that has 'mode 6' readability. I personally use the Blue Driver. It has lead me to the source of multiple small issues (including random rough idle). Firing the parts cannon at something is great for learning. And more power to you in that. But, it can get expensive. And it doesnt jave to be. Keep on keeping on.

The engine mounts can cause a vibration or also that one may feel as a loping at idle. I had to change my 2004 Envoy engine mounts and it made a big difference. The throttle body should be cleaned gently and no cleaner run down into the electronics that operate the throttle. The throttle plate is not supposed to be moved by hand either.

Almost wondering, IAC? If you've already replaced it, Mightn't it be bad from the factory?

Hi Jimmy Concerning the ruff idle, sometimes running the engine at lower rpm at idle can cause a ruff idle and intermittent shut off because the engine is not getting the right mix of air and fuel, try turning the idle up. E.G. If idling at 500 rpm try turning it up to 600 rpm and so on. If that doesn't work try a adjusting the air to fuel mix to see if it is that was the cause of the ruff idle, if all is controlled by a ecu then a retune may be needed of the ecu settings. If that does not fix it then the wiring loom needs to be looked at because the ecu and the wiring loom especially the connectors to the sensors are a weak point in the electronic fuel control system.

Check into your downstream O2 readings. Compare it to where it should be... My father in law changed the transmission out of his 06 trailblazer I6 due to a rough idle and a "slip" condition. Turns out his catalytic converter was quite plugged, but plugged enough to set a code. Weird I know but changing out the cat fixed his problem... Don't know if that helps but it's worth looking into.

Fuel injectors clean and how old is the fuel filter? I'd double check for vacuum leaks. I used to just get a water bottle and put a small hole on the top and squirted over the engine. Definitely do the basics first like these. When I an auto tech, a lot of idle issues were due to maintenance like injector cleaning.

The rough ideal if the battery was disconnected probably the vehicle is just having a hard time relearning its map (An engine map is essentially a table of data that is used to tell the engine what to do in certain situations.)

These engines are known for pumping the cylinder head full of oil(prolly bc gm was scared of grenading engines with the new vvt/dohc setup) and those spark plug gaskets will seep oil especially on the inner spark plugs(cyl 3,4) and coils causing intermittent misfires that often go unnoticed for very long times.

Was there any slack in timing chain? Takes very little slack to throw sensor off

Also check for a clogged cat. I used "cataclean" recently on my 2007 hummer with 3.7. It runs better and better fuel economy. I also used it on my 04 6.0 powerstroke and fuel millage is better. Clogged cats can cause rough idle.

how much fun was it to get to that last bolt by the firewall for the intake manifold. iykyk

I was an auto mechanic in the 80s for 8 years. I thought those cars were a pain to work on with all the emissions controls and the start of electronics controlling everything. Hats off to the auto mechanics today you really earn your pay, the way these cars are built today.

Mr parts cannon! Auto zone loves guys like you 😂😂😂😂😂😂

Great video. So here is ho2 a mechanic solved this same issue on my gmc. Mine has 324k , so it is no spring chicken. He reset the computer with a scanner. And then was watching fuel trim. As we drove around , the computer kept adding 10 15% fuel. In 3 minutes he said need injectors cleaned or buy new one. Once the new injector was in , it was better but not perfect. He looked at map sensor data , and it turned out it was responding too slow. Change that and iys been running like new (as new as it will get lol) ever since. Hope this helps

I used cheap Rock Auto Coils, Injectors and used alternators off Ebay to keep my 408,000 mile NY 05 Colorado on the road. I used Mobile 1 since brand new and changed oil every 6000. All the rough running I've ever experienced is due to harness corrosion especially to coils and injectors. If you don't tighten your coils enough. You will get oil in the plug holes.

I would suggest maybe changing the engine and transmission mounts. It's possible that the rubber in one of them is ripped and causing a slight shudder.

Did you put a code reader on it? The engine light might not be on but I bet there’s a code somewhere.

7:09.. For 65K, that engine is clean! I had a 2007 Mustang GT, it would stall out, glitch, and throw codes for cam position and crank position codes.. One day I went to start it and the brand new battery was completly flat. That's when I realized it was a failing alternator the whole time.

I'd run a few tank fulls of fuel injection cleaner and wait for the results before doing anything else. Go heavy mixture each time.

Do you need to do a throttle body relearn since you had it off that should take care of the issue

That mileage is gold. It's 25 miles above 65,536, or 5^2 + 256^2

I've own a 2004 Trailblazer for 15 years. I bought it with 65k miles. It has 191k miles now and still has 4 stock coils. It run great and has never fail an emission test. People trip me out when they change all 6 coils when the engine start to run funny. When the coils are bad. You will know it because you will get a skip.

Do a compression test Than a leak down test to see if there's any problem with the cylinders You need a good baseline

The quiet of the garage, hearing the crickets, so, other mechanics are insomniacs too.

Did all this on my '04 Envoy about 4 years ago at 260K miles, plus changing the fuel injectors. She's got 296K on her now. I notice you didn't show getting to that rear-most intake bolt. What a PITA. By the way, I thought mine was idling rough...change your motor mounts. Not that hard. Makes a world of difference.

Gunk on throttle body plate. Give it a good cleaning and see if it changes things. My 5.3L 2013 Avalanche's throttle plate was pretty caked. A toothbrush with some intake cleaner smoothed things out quite a bit. Still not perfect but does WAY less throttle wobbling.

Are you sure it's not a transmission problem. Have you run a scan?

That stumbling can be tough to diagnose, especially when no engine light comes on. There are a couple things you can check if you have an OBDII reader. Most obd readers give mode$06 data, which has test results for the monitored systems, there could be logged misfires on a particular cylinder. And then checking the total fuel trim (long-term fuel trim + short-term fuel trim. Or ltft stft.) Most manufacturers won't set a fuel trim fault until the total is +20% or -20%. Fuel trim is a command, i.e., sensors telling the computer add or subtract fuel. That rattle noise at the beginning of the video souded like a water pump or fan clutch failed, and I've experienced a faulty fan clutch causing idle concerns on many vehicles.

How did you get the back valve cover bolts out?

Best tool for finding that tick is a mechanics stethoscope. Best tool for finding a leak is a can of carb cleaner. Just spray around any potential vac leak and listen for stalling.

Sounds like Idle air solenoid, usually just cleaning them works, but cheap to replace. Also check the temp sensor reading with scan tool (sensor in intake)

Check the tensioner pulley. They have a tendency to wobble and cause a noise at idle. Watch for wobble with a go pro.

You need to swap out the Winter air for Spring air in your tyres, mate. Cheers from the UK!🇺🇸🇬🇧

Ruff idle is usually a cam position sensor and or crank position sensor and your around mileage they will need changed give or take. Also when the catalytic converter starts plugging up it will cause weird ruff idle and other symptoms that are not consistent at all.

I agree with the last guy. Check your fuel delivery system! You could have a failing pressure regulator or a damaged fuel pump!