94 Corolla rough idle when cold

[Jeffs2006EvoIX]

Originally Posted By: michaelluscher
I assume you did the basics?
Checked ignition system integrity?
Cleaned throttle body with TB cleaner and MAF with MAF cleaner?
Intake air ducting is all correct, no leaves?
Clean your IAC valve


I agree with all of this ^^^^^ plus it could be even a bad batch of gas, or poor quality gas your using. Could be several things. Have you hooked it up a code reader and see if anything comes up?

These are solid cars, it has to be something simple.

Jeff

 

[Rolla07]

Intake gasket. I had exact same issue on mine, despite mine being an 07.

 

[Drew99GT]

Originally Posted By: PandaBear
This car uses MAP instead of MAF, or I would have suggested a cleaning. It also have non easily adjustable valve clearance (need to swap disks) so I'd leave that alone. It usually shouldn't wear out of spec.


I did the valve clearance about 40,000 miles ago. 2 exhaust valves were tight and 2 intake valves were slightly loose.

I checked the bolts on the 02 sensor and they needed snugging up. Perhaps that was causing a slight exhaust leak.

I also bought CRC throttle body cleaner and sprayed a bunch through the idle air control valve from both ends. It seems to idle a bit better now, but time will tell when we get another shot of cold air. Like I said, it only does it when temps get below 40 degrees or so.

I was looking at my car and there is some kind of coolant activated temperature sensor threaded in by the coolant temp sensor; it has 2 vacuum lines, one to the charcoal canister, the other to a the throttle body. I can't find any info in the Haynes manual or online what that thing is; anyone know??? Perhaps that is the culprit.

 

[Drew99GT]

Originally Posted By: Phishin
Did you check the EGR valve? I could be stuck. Not sure it's common on your Toyota, but I've seen this happen enough times and it was the EGR that needed cleaning. Sometimes, it just needed replaced.

If you do replace it, search the interweb. Some cars are VERY picky about having only OEM EGR valves, while others could care less.


I lucked out and got a non Cali emission equipped Corolla with no EGR valve.

 

[PandaBear]

Originally Posted By: Drew99GT
Originally Posted By: Phishin
Did you check the EGR valve? I could be stuck. Not sure it's common on your Toyota, but I've seen this happen enough times and it was the EGR that needed cleaning. Sometimes, it just needed replaced.

If you do replace it, search the interweb. Some cars are VERY picky about having only OEM EGR valves, while others could care less.


I lucked out and got a non Cali emission equipped Corolla with no EGR valve.


Talking about Cal emission. Do you have any exhaust manifold crack? I had one cracked (Cal emission) and was having exhaust leak right before the O2 sensor hole.

A loose O2 sensor could cause rough idle if I remember right.

 

[eljefino]

Originally Posted By: Drew99GT


I was looking at my car and there is some kind of coolant activated temperature sensor threaded in by the coolant temp sensor; it has 2 vacuum lines, one to the charcoal canister, the other to a the throttle body. I can't find any info in the Haynes manual or online what that thing is; anyone know??? Perhaps that is the culprit.


Purge valve or part of it. It would not harm it for a bit to plug the hole at the manifold end of things. Eventually it would start reeking of gas.

Conversely you could tee a vacuum gauge into the EVAP system side of it and see if and when the vacuum appears, if it coincides with the roughness.

 

[Quest]

yes, it's a thermal activated vacuum valve, driven by manifold vacuum.


Note: EVAP canister purging can only happen when the engine coolant temperature is up (to normal), and that's when the vacuum valve turns it on.

If you suspect that it's faulty, you shall be able to attach a vacuum gauge such as mitivac handheld or similar @ the outlet side (where it connects to the EVAP canister) and have the engine running and check to see if it reads a vacuum (cold/hot) or not. It should read vacuum when hot, if memory serves.

Q.

 

[chrome]

Drew,

Need to establish if the rough idle is due to a cold misfire, or just the increased vibration you feel during a cold start.

When idling in cold, feel the exhaust pulses from the tailpipe and try to detect any inconsistent pulses which will suggest a misfire. Then can proceed from this angle.

If the rough idle is really just increased vibration, you may simply be looking at new engine mounts.

 

[Merkava_4]

Sounds to me like the computer doesn't know how cold the engine is.

The computer needs to know how cold the engine is so it can enrich the fuel mixture for cold starts.

 

[Drew99GT]

Originally Posted By: Quest
yes, it's a thermal activated vacuum valve, driven by manifold vacuum.


Note: EVAP canister purging can only happen when the engine coolant temperature is up (to normal), and that's when the vacuum valve turns it on.

If you suspect that it's faulty, you shall be able to attach a vacuum gauge such as mitivac handheld or similar @ the outlet side (where it connects to the EVAP canister) and have the engine running and check to see if it reads a vacuum (cold/hot) or not. It should read vacuum when hot, if memory serves.

Q.


Thanks Quest.

Well, it seems cleaning the IAC valve has solved the issue for now. I ran half a can of CRC throttle body cleaner through it. Filled the entire IAC ports in the throttle body till it ran out both sides of the throttle blade. If anyone reads this and does this procedure, you have to stick your finger over the inlet port while the car idles to create enough vacuum to suck all the fluid through.

 

[eljefino]

Originally Posted By: Drew99GT


Well, it seems cleaning the IAC valve has solved the issue for now. I ran half a can of CRC throttle body cleaner through it. Filled the entire IAC ports in the throttle body till it ran out both sides of the throttle blade. If anyone reads this and does this procedure, you have to stick your finger over the inlet port while the car idles to create enough vacuum to suck all the fluid through.


What you're doing is "teasing" it by lowering the idle enough that the valve opens. Release your finger and it should overshoot its target idle and adjust. IOW you're exercising the valve as you clean it, a good thing.

Off topic it's funny how we've becomed conditioned to computer controlled idle-- get off by 100 RPM and you hit a resonant frequency with the exhaust or mounts and it seems "off". Go low by just a few RPM and you lose a little healthy vacuum, same thing.

 

[Drew99GT]

An update to this thread; the symptoms continued and I found a video on Youtube that addresses how to properly clean a Toyota IAC. I had no idea that the fresh air side of the PCV system hooks to the IAC assembly on the underside of the throttle body on most Toyotas. If you spray cleaner into the IAC port while the throttle body is on the car, all it does is drain into the crankcase.

Sweet, I've been driving around for the better part of 500 miles with half a can of CRC throttle body cleaner mixed with the oil...

You have to take that hose off and plug it, take the coil off the IAC valve shaft, fill the IAC with cleaner, and rotate the shaft back and forth to free it and clean the gunk. Idle is much better on my car now, but when it gets warm, I'm taking it all apart for a spit shine cleaning. Just ordered a new gasket.

https://www.youtube.com/watch?v=WsP2-HKz7vE

 

[CharBaby]

Thanks so much, that was a GREAT video!

Although I have cleaned the TB & IAC in the past, I am starting to get another vibe at idle recently! I will use this on the Lexus in my signature this coming Spring/Summer

 

[Sequoiasoon]

I had a '93 and there were many threads on toyotanation about same sort of problem. Mine had 2 coolant temperature sensors. One was just for open loop when car was cold. Mine started with rough idle and in a short time on cold days (20's) it would barely run without keeping foot on throttle.

Changed that sensor and all was well. One was a 2 wire the other three wire. 2 was for electric fan, 3 was ECU.