runs lean when cold

DMRK · 11-27-2007, 03:39 PM

My car runs lean (have an A/F gauge) when it is cold outside (below 32). Runs poorly then like a flick of a switch it runs great. The colder it is the longer it seems to take.

I figured it is either the temperature sensor I in the AFM or the DME temperature sensor in the block. Could anything else cause this condition? What else controls the fuel mixture?

Checked the DME sensor per clarks garage with outside temp at 55F, It read 4.1K. Did not check it after warming because I dont have a problem when it is warm.

Havent yet checked the temp sensor I in the AFM. Is this replaceable? Or do I just buy another AFM.

Thanks

DMRK · 11-27-2007, 09:00 PM

what about the Throttle body enrichment switch?
Anyone......anyone.......Bueller!

andrew4266 · andrew4266's Garage

sounds like your o2 sensor is taking some time to warm up. as they age they take longer to do this.

Makis · 11-28-2007, 10:28 AM

Quote:

Originally Posted by DMRK

Checked the DME sensor per clarks garage with outside temp at 55F, It read 4.1K. Did not check it after warming because I dont have a problem when it is warm.

Thanks

How did you check this one? I had mine go bad and it also measured around 4.1K across the two terminals but when I measured the terminal against the ground one of them was shorting. So make sure both terminals are isolated from the ground. My was so bad I could not even start the car as the DME was thinking I have a warm engine when the engine was cold so start mixture was completely wrong.

DMRK · 11-28-2007, 06:02 PM

Quote:

Originally Posted by Makis

How did you check this one? I had mine go bad and it also measured around 4.1K across the two terminals but when I measured the terminal against the ground one of them was shorting. So make sure both terminals are isolated from the ground. My was so bad I could not even start the car as the DME was thinking I have a warm engine when the engine was cold so start mixture was completely wrong.

I'll have to check to ground, thanks

Gary2397 · 12-03-2007, 01:45 AM

You may also want to check the Auxiliary Air Valve is working right or not.
These valve provides an extra air for Air/Fuel Mixture when the engine is cold.

DMRK · 12-03-2007, 02:47 PM

I dont think my car has an Auxiliary Air Valve. I think thats just the early cars, mine is an 87.

Am I correct in thinking that G is the cold start valve?

Gary2397 · 12-04-2007, 01:43 PM

Then, it is Idle Control Valve which is similar to Auxilliary Air Valve. It maintains and adjusts the speed whether the car is cold or hot.
Find out if it is dirty or defective. Chances are it will get dirty if you have an AC.

DMRK · 12-04-2007, 05:26 PM

Thanks,
I'll take it out and clean it up see if it helps. Any idea on how to ohm it out to check it?

Makis · 12-04-2007, 06:42 PM

Quote:

Originally Posted by DMRK

Thanks,
I'll take it out and clean it up see if it helps. Any idea on how to ohm it out to check it?

Yes, is just a solenoid so it will have very low ohms not more then 5-10ohms. I think usually is stuck open and when you apply 12V it shuts. The ecu I think it pulses it so that it can control the amount of opening. It is possible that is stuck open and as a result the engine runs lean but a faulty Idle control valve will also cause idle problems when the engine is warm. So it is unlikely your problem.

DMRK · 12-04-2007, 07:16 PM

Quote:

Originally Posted by Makis

Yes, is just a solenoid so it will have very low ohms not more then 5-10ohms. I think usually is stuck open and when you apply 12V it shuts. The ecu I think it pulses it so that it can control the amount of opening. It is possible that is stuck open and as a result the engine runs lean but a faulty Idle control valve will also cause idle problems when the engine is warm. So it is unlikely your problem.

I can check it anyway to see if the coil is open, easy enough. But I don't think that is it.

What about the Temp valve (G in the pic)? How does that affect the Shutoff valve (H)? Any ideas?

Thanks for the help!

Makis · 12-04-2007, 07:52 PM

Quote:

Originally Posted by DMRK

What about the Temp valve (G in the pic)? How does that affect the Shutoff valve (H)? Any ideas?

Thanks for the help!

Not familar with this system as I don't think I have H on my S2. It is possible that this is your problem. I am not sure, but if G fails and lets vacuum activate H from cold and H is be open. This allows air to flow into the manifold bypassing the throttle body in the same way the idle solenoid does which can cause the lean mixture you are seeing when cold. Worth checking, probably disconnecting the vacuum line to H when cold and blocking it to avoid any vacuum leaks will be a quick test.

DMRK · 12-04-2007, 08:45 PM

Thats kinda my thoughts too, thanks I'll give it a try.

I was also thinking about hooking up a 5K pot on the leads for the DME temp sensor to rule it out completely.

Makis · 12-04-2007, 10:40 PM

Don't worry about the 5k just disconnect the sensor and run the engine cold. You should be able to tell if it is better within a minute.