Cold running problems on 3.2

[DJB]

My 86 3.2 Cab has developed a problem of dying when it is cold.

It starts very easily and will happily idle, however while it is cold it will cut out while being driven and no throttle applied. Once must heel and toe constantly to keep the enging running in traffic and at traffic lights.

The tacho seems to drop quickly to say 300 rpm and under normal conditions will bounce back to 800 rpm, when cold it does not recover and the engine stalls. Once it is warm, after say 15 minutes, it runs just fine.

I have carried out a few checks, the mixture is fine (co2 levels). The idle position switch has electrically tested OK. I have tested and cleaned the idle speed control valve and this seems to working within the specs. All electrical earths have been cleaned and tested.

I am a little stuck as to the next thing to test, any ideas....please!


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[nhromyak]

Not sure if the '86 has the Knock sensor, check this.

Does your '86 have the updated Head Temp Sensor.

Also check the O2 sensor. I could see if this is a "lazy" O2, you would get these symptons.

If nothing else, I bumped your post back to the top for the "WELTMEISTERS" to see!

Good Luck.


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Nick Hromyak
'85 Carrera 7 & 9 Fuchs
Havin' Fun in Sacramento

[DJB]

Thanks Nick,

Bently suggests that the O2 Sensor will not affect idle speeds - is this correct?

An updated head temp sensor - how can I check if it is the updated model?

Thanks for your assistance.
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David
86 Cab
Sydney
Australia

[nhromyak]

Interesting you mention the O2. Many people commented (me including), disconnect the O2 stabilizes the RPMS to 850 (+/- 50). Then I got BAD gas mileage.

Now that I think about it, your O2 shouldn't even be "on" when the engine is cold, as it probably hasn't warmed up yet. O2 takes over 300 (I think) degrees to run correctly.

Did you replace the DME relay?
Should always carry a spare, I do.

The updated head temp sensor should have two wires coming off of it. If it only has one, you have the older style. I think this should only come in to play when the engine is hot though.

You might want to check your MAF sensor. I think this the "barn-door" just inside the air cleaner. I am not sure how to check it, but you can make sure your connector is on it tightly. Also, disconnect it and see if you get a variable OHMs resistance as you move the door on some of the connectors. Be sure to use a DVOM, and analog VOM might damage the MAF ($).

OK LETS KEEP IT SIMPLE.

What was the last thing done?
Check the intake bolts for tightness.
Check for any vacuum leaks.
Check for correct IDLE speed. Adjust as necessary.
Check Idle speed valve for proper operation. I think if you put your hand on it, you should feel it pulsing.

Hmm, not sure what else would cause cold running or idle problems.

Good luck.
Nick H.

[This message has been edited by nhromyak (edited 08-27-2001).]

[jthwan22]

I am pretty sure 3.2L does not have a knock sensor



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1984 911 Cabriolet

[DJB]

Thanks for the advice so far gents.

I am also sure that there is no knock sensor on a 3.2.

What part does the temp sender play at low temps, maybe this could be the cause.

I am not sure if the relay would affect the operation, as this acts basically as a switch - if it failed it would be off... is there any other reasoning behind this suggestion?

Thanks