I think your biggest clue here is that the idle is still "wonky" after you assembled everything. I'm going to take a wild guess that they car may be getting unmetered air causing a rough running / rough idle condition causing a misfire. Check that the throttle body and IAC is installed and torqued correctly. I hope you replaced both the throttle body gasket and the IAC gasket. You can get BOTH from RockAuto.com. Check that the gasket is in place, not folded over / missing / misaligned. After you check that, then check / replace your spark plugs and air cleaner. Watch my video again on how I "checked" the operation of the IAC valve. Get back to me...

P0171 for a Toyota Celica is System Lean - not getting enough fuel. I understand that you put the original throttle body back into place. Can you verify the model, year, and engine of your car? Is it a 1zz or 2zz engine? I really think you have two different problems here. I don't think they are related. The high idle problem I feel is your main problem that prevents you from driving the car. I would watch this video and watch what I did to remove, disassemble, clean the IAC valve. Watch right to the end of the video and see what I did to test the IAC is working or not. I ran a very simple test, without the use of scan tools, to see if the ECU has control of the car's idle. I'm not sure if your mechanic knows this, but when you're throttle body is closed, it doesn't close all the way. The throttle body remains open approximately 10 to 12%. Because if it didn't, how else would a car get air to idle? As for the P0171 code. My general advice moving forward, is to check all the easy things first. Replace air filter, replace the spark plugs, check this front plug wires, check the wiring going to the fuel injectors, make sure you have fresh fuel, perhaps run some fuel injection cleaner in the tank not just once but a few times. Generally, make sure that tune-up condition is in excellent shape and then you can proceed with the diagnosis. Unfortunately, without a scan tool that can give you live data, you are left with the only option which is to replace Parts until you fix it. To me, is unlikely that a MAF sensor cause this issue. MAF sensors are pretty reliable, they are not known to fail for this generation of Toyotas. However, depending on the model and age of the car, oxygen sensors don't last forever. You should be looking at the forward oxygen sensor in front of the catalytic converter. But to properly diagnose the O2 sensor, you need a scan tool that you could look at the data, I would also argue that you need an oscilloscope to take a closer look. I know that there isn't any oxygen sensor codes but remember a sensor can be malfunctioning, yet remain Within normal operating range. I would also have liked to see the long-term and short-term field trim data. If the car is running to lean, that means the ECU should be trying to add fuel which means the long-term and short-term field trim should be above 100%. Regardless, you need to fix a high idle problem before you fix theP0171 code. My final piece of advice to you, is to go on Toyota, or Toyota Celica message forms on the internet. There are plenty of forums out there with people who really love Toyota Celica such as myself. They can offer you some insights into your issue. This is an excellent platform to share pictures and videos and get the opinions of other silica enthusiasts. I'm active on www.toyotacelicas.com/, my name there is daddytroopa.

Thanks for the information and reply..I change the spark plugs, the maf sensor and the intake manifold gasket basically everything except the o2 sensor i didn’t change..but the mechanic did a 02 sensor check and said the sensors are good and they did a smoke test with no leaks but the smoke was coming out of the airbox and they said that the throttle body is no good. But i can add numbers what the scanner is give me..and it a 2001 toyota celica 1z engine..it all original Load pct is 20.8 Etc is 203 Shortftl is 7.8 Longftl is 32.8 Vss is 0 Iat is 93

Let me know how it goes, ask questions if you have any.

@@geekynewz I think I'm having some major problem here, I have try a lot of DIY, maybe I need to take it in to a professional mechanic , I've buy new iac, new maf and tps, I've also check for vacuum leaks , clean throttle body still have the problem, even gotten worst to the point of it shutting off when I drive and come to a stop.

@@celicasinjaOk I see that you've already replaced the TPS, MAF and IAC. But lets back up a bit. Can you describe the original problem to me in greater detail? Before we go around and replace all of those parts, a diagnosis always starts with the easy things. - Any check engine light / engine codes? - Are the spark plugs in good condition? - Air filter, fuel filter OK - Check for obvious faults in wiring, harnesses, connections, grounds - Is the gas fresh? - Oil and coolant in good condition - Any signs of water intrusion, rats / mice damage - Good / clean battery terminals - Good / clean ground connections Once you check the easy / obvious stuff, then you get deeper. - I would check the crankshaft sensor located under the water pump / AC pump. - Check fuel pressure (special tools needed) - Scan the live data (need a pretty good scan tool to do that, Autel MK808) - Check the valve timing (need to remove the valve cover to do that) - Check cylinder pressure / compression test (need special tools)