86 951

Cold start up: 45F.

Engine lopes and idles erratically for a couple of minutes on cold start. Open the throttle a bit and it's happy. Idle is perfect when warm.

AFR shows full rich - 10.0, then as engine warms settles to stoich - 14.7.

Vacuum at hot idle is around 17-18", around 12-13" at cold idle. Normal?

I believe the DME temp sensor is off scale (very high resistance) when "cold", perhaps giving the DME a value that would appear at a much colder temperature.

Lastly, is the ICV active whenever the engine is running? I would suspect it so as the factory procedure for idle set requires a warm engine and disabling of the ICV via the test port.

Thoughts?

 

Engine management systems naturally run a little richer at startup. In addition, you need to wait until the engine is warm before your AFR gives a correct reading.

 

Is this something new, or it always ran rich at cold star?
Possible causes:
- Warm up cycle too aggressive/rich - Must be addressed in the chip
- TPS is not reading Idle when TB is closed - check TPS
- Bad Engine Temp sensor - check cold resistance.

 

It's been odd when cold for as long as I can recall - bought it last year.

It has exhibited this behavior with both stock and aftermarket chips.

Does the DME determine proper mixture values based upon the temp sensor output until the O2 has heated to proper temp?

Regarding the TPS switch, doesn't it make sense that if it were bad - idle would be poor all the time?

 

My understanding is the DME will run the car a bit rich until the block/coolant is up to temp as gaged by one of the two temp sensor in the block...I can't remember which one though.
I think it's the one in the front of the engine with the blue connector on it though. I rewired this connector at some point and it cured my rough idling last winter.

 

If the Idle switch is sending a PT signal, it will be running off of the PT tables when it should be running off of the Idle tables. Other variables are affected as well, add to it the increase in fuel for the cold start and the problem is magnified.
When warm, the cold start does not have as much of an effect, meaning you may not notice the rich mixture.
Again, this is something I have seen before. It may or may not be the cause of your problem.

Since the behavior is the same with the stock or aftermarket chip, I assume a sensor is causing the problem.

 

I'll check the TPS and temp sensor.

If I find anything, I'll be sure to post a follow-up.

Thanks

 

I believe that I have located my "problem".

It seems as though there is something going on with the idle control valve.

When the car is idling, a tap on the valve causes idle to drop (and stay), another tap and idle is back to normal. This tapping on the valve yields a different idle speed each time.

Wiggling the electrical connector produces no change in idle, I'll assume the problem is mechanical - as though the valve cannot open fully.

TPS and DME temp sensor checked out fine.

Try a new ICV for $150?

 

$ 150.00 for the ICV , where at the dealer?

 

Paragon. You know of somewhere to get a NEW valve for less?

 

Hey tyro,

I just responded to your PM. As fast951 stated above in some cases the fuel enrichment has to be scaled back to relieve this issue, but I've never had to do that with stock injectors and an AFM. I do on some MAF cars and with larger injectors it is a pratice. So it could be a bad sensor. I just wanted to add that if it has been doing this for a while you probably need a fresh set of plugs, running that rich really cruds them up.

Regards,
Russell

 

I'm certain the ICV is at fault. I feel that a tap on the valve shouldn't make the idle speed decrease or increase.

The valve is 21 years old, time for a new one. No reason to stop spending money now!

 

If the ICV is sticking, before you get a new one, soak it internally with WD40 (or similar prodict). Let it soak overnight. You might need to do this 2-3 times, it might free it up.

You might still have a cold enrichment issue.

 

Finally got around to fixing my problem. A new idle air valve works wonders.

Best of all, I was able to get it out without removing the intake!

Thanks for everyone's help and insight.

Have a look at the condition of the old valve:

 

Sounds like your problem is my problem. Besides stopping the idle from "looping" on startup, did replacing the valve stop the car from running rich as well? Did your car run a little rich even after warm up prior to the new valve? Do you think that cleaning the valve would have solved the problem, or was it too far-gone to bother? It's a bit of a stupid question, but I assume the turbo spooled in this "erratic" idle, and was it really loud? I'm just trying to figure out if my problem is the same - it sounds exactly the same to me.