Lately my car's been idling rough. It'll sit in the 200-300 rpm range and kind of bounce every once in a while. I'm thinking maybe the MAF's clogged or the air filter needs to be replaced. Anybody know what else this may be from?
mine ususally idles at around 700 or 800 but sometimes when im at a stop it get low to 300 and cuase my car to vibrate...could that be a sensor prob???
It's the IAC (what Haulin was talking about but misspelled ). You need to get some throttle body cleaner and spray it at the hole inside the throttle body. It's a square hole on the front half in front of the throttle plate. It allows air past the throttle plate at idle, and the IAC (Idle Air Control valve) opens and closes depending on how the car needs to idle.
The problem comes in when the PCV system is active. The PCV system recirculates any excess oil and gas vapors into the intake system to burn them, instead of releasing them into the atmosphere. These fumes have to go through the IAC at idle, and will condense into liquid form after a while. Unfortunately, it's more of a sludge than a liquid, and this sludge gums up the IAC, limiting its ability to open and close (it's only operated by a magnet), so your idle can become irratic after a while.
The vapors also condense on the throttle plate and inside the intake manifold, so spraying them clean will improve airflow and performance a bit. When the vapors enter the combustion chamber, they collect on the valves and piston tops and create carbon deposits. You can use this stuff to clean out most of the intake system, and help the fuel and oil system as well:
Though, Haulin was wrong about adjusting the idle. The butterfly valve has nothing to do with the idle speed. It's just there to reduce low RPM engine noise. It opens between 3000-4000 RPM to let more air into the engine, and there is no adjustment for it (it's controlled by the engine's vacuum). The only way you can adjust the idle on the Celica is to get the Apexi PowerFC. The idle is controlled entirely by the ECU, so even tightening the throttle cable to increase it will be cancelled out by the ECU closing up the IAC to compensate. It's not instantaneous, but the ECU will catch on after a little while and reset it back to OEM specs.
BTW, an oil catch can attached to the PCV system will help keep the IAC clean, and reduce carbon buildup a ton. Packing it with stainless steel scrubbers (the kind you use to wash pots and dishes) will help the vapors condense faster, keeping them in the can instead of flowing back into the engine.
Though, Haulin was wrong about adjusting the idle. The butterfly valve has nothing to do with the idle speed. It's just there to reduce low RPM engine noise. It opens between 3000-4000 RPM to let more air into the engine, and there is no adjustment for it (it's controlled by the engine's vacuum). The only way you can adjust the idle on the Celica is to get the Apexi PowerFC. The idle is controlled entirely by the ECU, so even tightening the throttle cable to increase it will be cancelled out by the ECU closing up the IAC to compensate. It's not instantaneous, but the ECU will catch on after a little while and reset it back to OEM specs.
Yes, I had the IAC acronym misordered. However I AM NOT WRONG about the butterfly valve. Do your homework. Ask anyone what happens when you manually open the butter fly. The engine revs up. Your throttle cable is attached & so is the throttle position sensor which tells your computer how much throttle you are seeking & it lets more fuel out the injectors. This screw is a idle adjustment screw. Its on both the GT & GTS; maybe not DBW versions, I donno.
Ah, I thought you meant the "butterfly valve", as in the butterfly valve in the stock airbox that everyone removes. Either way, the ECU will just revert the opening of the throttle body, whether it was done by moving that screw or by tightening the throttle cable. If your car is functioning properly, the throttle shouldn't need to be messed with. Many people have tried this, and all have had their ECUs reset the idle to normal, much like S-AFC users have had their ECUs reset to the normal fuel levels. Our ECU doesn't like to be messed with.
Ah, I thought you meant the "butterfly valve", as in the butterfly valve in the stock airbox that everyone removes. Either way, the ECU will just revert the opening of the throttle body, whether it was done by moving that screw or by tightening the throttle cable. If your car is functioning properly, the throttle shouldn't need to be messed with. Many people have tried this, and all have had their ECUs reset the idle to normal, much like S-AFC users have had their ECUs reset to the normal fuel levels. Our ECU doesn't like to be messed with.
But I think the point he's getting at is that if your idle is super low, like mine, that if you adjust, the car WILL adjust it back to normal and make everything fine again.
Actually its pretty standard for the dealership to adjust the idle. Once you put on say 50,000 miles, the engine never idles as smooth. Bumping the idle up a few hundred often smooths it right out. My dealer did mine once during a regular service visit.
Ah, I thought you meant the "butterfly valve", as in the butterfly valve in the stock airbox that everyone removes. Either way, the ECU will just revert the opening of the throttle body, whether it was done by moving that screw or by tightening the throttle cable. If your car is functioning properly, the throttle shouldn't need to be messed with. Many people have tried this, and all have had their ECUs reset the idle to normal, much like S-AFC users have had their ECUs reset to the normal fuel levels. Our ECU doesn't like to be messed with.
But I think the point he's getting at is that if your idle is super low, like mine, that if you adjust, the car WILL adjust it back to normal and make everything fine again.
No, if you up the idle manually, the ECU will eventually reset itself and bring your idle back down to being too low. The ECU has set parameters for idle and open throttle percentages, which is how it knows if you messed with the idle (same reason it idles high when the engine is cold, or when idle rises when you turn on the AC). If you keep adjusting the idle, though, eventually you'll get to the point that the IAC is already closed, so you'll stay at that idle speed. Unfortunately, if you do it by adjusting that screw, you'll have a lot of free play in the gas pedal. If you do it by adjusting the throttle cable, you'll bend the throttle rotor, since you won't be able to push the pedal all the way to the floor anymore.
Good idle can last the lifetime of your car as long as you keep the IAC and MAFS clean. They're the keys to your car's idle (along with the coolant temp sensor and O2 sensors).
I have a 2000 Toyota Celica GT VVT-i 1zz engine. Like everyone here, her idle fluctuates between 750 RPM (normal) and 50 RPM (not normal) This happens regardless of being warmed up or cold. So far I have cleaned my old Mass Air Flow Sensor (MAFS), then I replaced my MAFS to be sure, replaced my PCV valve, made sure there were no hose vacuum leaks, replaced my injectors ($25 each from partsgeek.com, which did make a huge difference in overall performance, but not at idle), removed and cleaned both the throttle body and the Idle Air Control valve, and of course new Air Filter. My Celica still wants to suffocate and die out at lights. I have one clue left... When I unplug my battery, and the computer naturally finds its idle level, she works for about a week, maybe two at Idle, and puuuurs like the day I bought her. But then after that time, my check engine light pops on (Code reads: engine running lean on bank one... so helpful since Celica's only have one bank) At this time, the idle problem returns. So here's my brilliant theory... It's a computer controlled element. Maybe the O2 sensor has gone bad? I mean, she's 17 years old, and I've owned her for 15. If it's not the O2 sensor, I am out of ideas.
Hi Celica hobbiests and Particle 9:) I know this is a 2 year late response to ur question, and for sum even longer! But i finally made a profile to give sum of my personal input and experience iv had with cars. Iv been a mechanic for a good amount of time and also fell in love with the celica(or as Japan named it the heavenly/celestial).so this could and should also apply to pretty much all of Seventh generation (T230; 1999–2006)toyota celicas I was recently working on idling issues and power lacking on 1 too many years too big of a project for sum folks..the 2002 celica gt!! which brought me here to look at what people think and what steps they have taken to resolve their issues. Great ideas people! before i continue with all due respect Ill correct Particle9..:, bank 1 is the upstream or very first o2 sensor closer to the engine, Then you have a 2nd downstream 02 sensor bank 2. These sensor just communicate with the pcm/ecu all the exhaust or burnt up trash that the engine created internally and now traveling to polute the air lol And that communication is used by the pcm/ecu to keep a smooth idle by modifying the air/fuel ratio mixture levels through the diff sensors placed all over the car... So when the upstream sensor receives too much air and the computer cannot correct it, ( in your case Particle9 )the engine light comes on and proclaims its running lean. Now this code lean means theres too much air, but it also means lack of fuel.(and as you mentioned could be a bad o2 sensor) I know your fuel injectors were swapped out, but being 25$each chinese brand compared to. 125+$ each can make a difference in the performance of the vehicle. Anyways..just my opinion. It doesnt have to be the most expensive injectors, referbished work very well too as long as they are a legit make for the toyota oems:)
So going back to the 02 gt i was working on the other day, this car was passed down by over 3 owners in about a 3 year span, sitting on their driveway in their garages! Each one willing to fix it up by throwing brand new parts at it. Of course thats a very expensive hit and miss..but after all 3 went bankrupt one by one it was gifted to me!;). So the maf was brand new, so were the sparks and coils, all types of gaskets replaced correctly and relays and connectors and wiring done. Mind that compression was pretty good. The throttle body was supposably cleaned with a bunch of products, but i know the iac valve in the throttle body gets filthy and after time the carbon builds up and it doesnt spin as freely as it did when it was brand new. That there is usually the main reasons for it to idle poorly if its not spark or compression related. For me, only one way to properly clean that valve..taking the throttle body off and taking the motor off the iac valve and cleaning it thourghly as best as possible without damaging it. There might be some videos on youtube of taking apart the Celicas iac valve and cleaning it very well. But just dumping a solution wont cut it on these cars im telling ya. If you take it apart and clean it correctly When finished cleaning that valve , the pin/spindle in the middle that lets iac in and the iac out outlets should spin very freely in both directions.. Alot of times thats where the search for answers when it comes to figuring issues of poor idle should be resolved but for my Celica of course it had continue lol. I had a bunch of different codes From multiple misfirings i was getting the last 2 codes of misfire in cylinder#2 and running lean in bank 1. (P0302 and i believe it was p0171) correct me if im wrong. Prior to that i was told some injectors were replaced and some rebuild. Tasting the injectors resistance with a multi meter made everything seemed fine and dandy. I decided it wont hurt if i swapped some injectors out to test cylinder #2 injector. Right? Well when i switched the bad injector #2 to another cylinders injector#4 and i put the #4 into the spot of the #2. Just a simple swap to test the actual component. (Btw, this is the same procedure that could be done with coils and spark plugs if wanted/ needed to perform this test.) After wiping codes and starting the car. Engine light came on and codes stored in the computer read cylinder #4 misfire detected lean bank 1.GREATEST NEWS iv heard in a long time!! Woopty doo-doo!! Ok so for my car it happened to be the actual injectors itself being partially clogged causing the cylinder to run lean and then making it misfire. But say for instance it still remained on the cylinder #2..after all the work of checking parts and installment. I would have to say that theres a good chance in the internal wiring or the ECU at fault. That means swapping a new computer and reprogramming it. Believe it or not, s***happens Well, Thats all i got for now! I know this is a long message and congrats you made it to the end. Im aware that not everybody has the knowledge and or experience of sum others. SoThats why i wrote this specific forum. Hope it helps you celica wonderers and lovers to success.. To Ultimately be able to get your car in a better condition and for sum getting it back on the road..and EVEN for sum that live into those special smog states. Being able to remove the engine light to receive a smog certificate! Rather then wasting time searching for answers online and throwing parts and loosing hope. You got it! Good luck and God bless you!:)
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). You need to get some throttle body cleaner and spray it at the hole inside the throttle body. It's a square hole on the front half in front of the throttle plate. It allows air past the throttle plate at idle, and the IAC (Idle Air Control valve) opens and closes depending on how the car needs to idle. 
