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Rough Idle #295541 Oct 9, 5:39am Oct 9, 5:39am
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2000 Silver Toyota Celica
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Rough Idle
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? confused


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Re: Rough Idle [Re: XxMerlinxX] #295542 Oct 9, 6:19am Oct 9, 6:19am
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its most likely the Intake/maf. i think all you have to do is just clean it.


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Re: Rough Idle [Re: VoodooGTS] #295543 Oct 9, 6:33am Oct 9, 6:33am

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Mine has been doing that lately. It will jump from 400-1500 at a stop. Its the MAFS and im sure cleaning the airfilter wont hurt also.

Re: Rough Idle #295544 Oct 9, 6:46am Oct 9, 6:46am
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Originally Posted by spyder00367
Mine has been doing that lately. It will jump from 400-1500 at a stop. Its the MAFS and im sure cleaning the airfilter wont hurt also.


For yours, if it's in the morning, that's normal. The car's just warming itself up. Later on while you're driving you'll notice it won't do it.


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Re: Rough Idle [Re: XxMerlinxX] #295545 Oct 9, 6:47am Oct 9, 6:47am

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Originally Posted by XxMerlinxX
Originally Posted by spyder00367
Mine has been doing that lately. It will jump from 400-1500 at a stop. Its the MAFS and im sure cleaning the airfilter wont hurt also.


For yours, if it's in the morning, that's normal. The car's just warming itself up. Later on while you're driving you'll notice it won't do it.
No its warmed up.

Re: Rough Idle #295546 Oct 9, 7:09am Oct 9, 7:09am
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clean the maf and throttle body.

Will work wonders if you haven't done it before.


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Re: Rough Idle [Re: DiabloGTS] #295547 Oct 9, 10:38am Oct 9, 10:38am
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AIC causes idling problems.

You can adjust the idle, there is an adjustment screw on the butterfly valve. Just adjust it to where you want it.

Re: Rough Idle [Re: Haulin_A_Doo] #295548 Oct 9, 3:52pm Oct 9, 3:52pm
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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???


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Re: Rough Idle [Re: xxmonkeyboixx] #295549 Oct 9, 3:53pm Oct 9, 3:53pm
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tighten your throttle cable..get ur rpms to idle to at LEAST 700 rpms (stock is 750..and a little higher doesnt hurt at all)

Re: Rough Idle [Re: Haulin_A_Doo] #295550 Oct 9, 4:26pm Oct 9, 4:26pm
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Originally Posted by Haulin_A_Doo
AIC causes idling problems.

You can adjust the idle, there is an adjustment screw on the butterfly valve. Just adjust it to where you want it.


What is AIC? confused


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Re: Rough Idle [Re: XxMerlinxX] #295551 Oct 9, 4:59pm Oct 9, 4:59pm
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It's the IAC (what Haulin was talking about but misspelled tongue ). 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.

Re: Rough Idle [Re: Blue_Bomber] #295552 Oct 9, 5:01pm Oct 9, 5:01pm
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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.

Re: Rough Idle [Re: Blue_Bomber] #295553 Oct 9, 7:11pm Oct 9, 7:11pm
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Originally Posted by Blue_Bomber

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.

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Re: Rough Idle [Re: Haulin_A_Doo] #295554 Oct 9, 7:27pm Oct 9, 7:27pm
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Ah, I thought you meant the "butterfly valve", as in the butterfly valve in the stock airbox that everyone removes. tongue 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. wink

Re: Rough Idle [Re: Blue_Bomber] #295555 Oct 9, 7:41pm Oct 9, 7:41pm
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Originally Posted by Blue_Bomber
Ah, I thought you meant the "butterfly valve", as in the butterfly valve in the stock airbox that everyone removes. tongue 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. wink


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.


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Re: Rough Idle [Re: Blue_Bomber] #295556 Oct 9, 7:42pm Oct 9, 7:42pm
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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.

Re: Rough Idle [Re: Haulin_A_Doo] #295557 Oct 9, 8:00pm Oct 9, 8:00pm
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WEIRD I was just thinking on making a post on this.. w000000t, thanks for the tips, Imma give em a shot... thumbsup


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Re: Rough Idle [Re: XxMerlinxX] #295558 Oct 9, 10:55pm Oct 9, 10:55pm
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Originally Posted by XxMerlinxX
Originally Posted by Blue_Bomber
Ah, I thought you meant the "butterfly valve", as in the butterfly valve in the stock airbox that everyone removes. tongue 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. wink


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).

Re: Rough Idle [Re: Blue_Bomber] #295559 Oct 9, 11:10pm Oct 9, 11:10pm
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Your talking about a 1/4" adjustment. You adjust the screw & then pick up the tiny bit of slack in the cable if any.

Re: Rough Idle [Re: XxMerlinxX] #451763 Aug 23, 10:01am Aug 23, 10:01am
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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.

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