rough idle when cold

[vwghia-guy]

Originally Posted by wild man

Pull off 1 plug wire at a time, while the engine is exhibiting the cold miss symptom, to determine which cylinder is "misssing". Then swap that fuel injector with one from a different cylinder. If the miss then migrates to the other cylinder, you have just confirmed that you have a leaky fuel injector.

Oh, in the off-chance that the miss stays with the same cylinder after the injector swap, it's likely that you have a valve guide seal that is toast. That is unless a spark plug is fouling, which could be checked in the same manner as an injector. But if it does turn out to be a spark plug, it is likely that one of the first 2 things mentioned is what caused it to foul.

I just recently replaced the cylinder head with a rebuilt unit. It has less than 3000 miles on it. I've checked plugs, and the cylinder head came with new valve stem seals. Funny thing is that as soon as the car is warm enough to blow warm air from the vents, it clears up.

I haven't tried your suggestion regarding swapping injectors. I'll add that to the list. FPR and damper get here tonight and I'll have them on this evening.

Thanks for the advice!

[vwghia-guy]

Replaced FPR and damper. Still have cold start issues! Got another engine temp sensor coming. Pulling at straws here. Anyone want an 89 S2?

[kmakovac]

i have the same problem on a 86" NA

after hours of work,try,change sensors and so on i change the air/fuel ratio on my AFM.

I put 2 to 3 cyrkle in "lean" counterclockwise and the situasion now is perfect.
I try to return the hex in the old position and the problem begin again but don't now what can happen.

Maybe with years there are lots of small vacuum leaks that change the demand of mixture.
Maybe the O2 sensor will have a wrong signal on cold????

Try this,without cost but remember the numbers of cycles so you can go in other direction if is worsth

[9FF]

This problem is most likely caused by either a bad O2 sensor or a bad DME temp switch. Not the FPR, Damper, Idle valve, AFM or other stuff mentioned.

Check those two things first. The dme temp switch is on the cyl head under the intake manifold at the front. There are two temp switches there, one for the guage one for the dme, it's the dme one you need to test/change. If that doesn't fix it test/change your O2 sensor.

Basically those two things will effect idle when cold, all the other stuff mentioned will effect idle cold or hot and if your idle is good hot then you are only left with O2 sensor and dme temp switch.

[vwghia-guy]

Thanks for the suggestions.

I have replaced the DME temp sensor. That made no difference. I have not replaced the O2 sensor yet; I did, however, unplug it. I was told that by taking the O2 signal from the dme, it would use a closed-loop map. And plugged or unplugged made no difference.

This problem didn't show up until I replaced a cylinder head. Compression is good and once warm it runs great. It just seems to be a problem that corrects itself when warm.

Could this be an issue with the reference sensor?

Still scratching my head.....

cds

Originally Posted by 9FF

This problem is most likely caused by either a bad O2 sensor or a bad DME temp switch. Not the FPR, Damper, Idle valve, AFM or other stuff mentioned.

Check those two things first. The dme temp switch is on the cyl head under the intake manifold at the front. There are two temp switches there, one for the guage one for the dme, it's the dme one you need to test/change. If that doesn't fix it test/change your O2 sensor.

Basically those two things will effect idle when cold, all the other stuff mentioned will effect idle cold or hot and if your idle is good hot then you are only left with O2 sensor and dme temp switch.

[vwghia-guy]

I give up!

Originally Posted by vwghia-guy

Thanks for the suggestions.

I have replaced the DME temp sensor. That made no difference. I have not replaced the O2 sensor yet; I did, however, unplug it. I was told that by taking the O2 signal from the dme, it would use a closed-loop map. And plugged or unplugged made no difference.

This problem didn't show up until I replaced a cylinder head. Compression is good and once warm it runs great. It just seems to be a problem that corrects itself when warm.

Could this be an issue with the reference sensor?

Still scratching my head.....

cds

[wild man]

This is looking more and more like one of those threads (stories) where decent amounts of $ are being spent on THIS new part, and THAT new part, only to see the problem NOT go away. It does pain me, to see it going on and on.

YOU NEED TO TROUBLESHOOT THE PROBLEM, MAN! The poke-&-hope approach only seems to be costing you $, but isn't getting any results. If adjusting the idle mixture (air bleed) screw doesn't take care of it, you need to narrow it down to what cylinder is misssing when cold.

Intake runner gasket leak when cold maybe?

Is the cylinder missing because it's too rich, too lean, or sparkless?

Did you say that you checked compression?

EDIT: I forgot to mention, it WON'T be the O2 sensor, as that does not even function when the engine is started up cold. And the loop is OPEN (not closed) if the sensor is disconnected, but that's how it operates on cold startups, anyways.

[wild man]

All right, I really want to help you here, so I am going to add to my last post.

After determining which cyl is the misser, closely inspect the spark plug, as it should show signs indicating whether it is running too rich or too lean. But don't do this after it has been running warmed up without a miss for ANY length of time. If it whitish/dry, it probably too lean due to that cyl sucking in extra air somewhere, or the injector getting clogged, relative to the others.. If it black/wet, it probably rich, but that could be for several reasons. One being that the injector leaks when the engine is shut down. Then when started back up, all of the fuel laying in that cylinder fouls out the plug, until it burns it up. The other thing that could appear to be making it too rich is engine oil. There is the possibility of a head gasket issue, allowing oil to drip into that cylinder, which would cause essentially the same effect as excess fuel in the cylinder on a cold start, fouling the plug until the engine warms up enough to cook it off. A defective, damaged, or incorrectly installed valve seal would also produce the same effect.

Ok, I gotta go now. I hope that gives you something to go on. Good luck!

[Tervuren]

I've had a similar issue with my '86 where it keeps dropping from edge of dieing, then comes back to life and spikes above idle, then drops back to about half idle. I'm rebuilding the suspension before I drive it, so I haven't fixed it yet.

However, I did notice that my in dash volt meter is is jumping and falling along with the rough idle, first thing I'll do next time I try to sort it out, is put a volt meter under the hood and see what is going on.

[wild man]

Originally Posted by Tervuren

I've had a similar issue with my '86 where it keeps dropping from edge of dieing, then comes back to life and spikes above idle, then drops back to about half idle. I'm rebuilding the suspension before I drive it, so I haven't fixed it yet.

However, I did notice that my in dash volt meter is is jumping and falling along with the rough idle, first thing I'll do next time I try to sort it out, is put a volt meter under the hood and see what is going on.

Now THAT really sounds like bad ground(s) somewhere.

[vwghia-guy]

Originally Posted by vwghia-guy

I give up!

Well, the S2 is at the Porsche dealer while I'm in Utah for 3 weeks. Got a call from the Porsche tech and apparently he's re-verifying all the troubleshooting I had already done. Fortunately for me the car has the exact same symptoms with him - starts well, then starts missing after running about 30 seconds - and finally clears up after about 3 to 4 minutes. The miss so far has occurred across all cylinders. Something is causing the all of the injectors to dump fuel into the cylinders. BTW, fuel pressure was spot on and within specs after shutdown. He troubleshot the TPS, AFM, Air Temp Sensor, engine temp sensor, and o/2 sensor and all are fine. He tends to think that a wire in the engine harness got broken/damaged during the head swap and is planning to ohm out all the wires in the engine harness.

I'll post more when I hear something.

chris

[guru944]

Initially my S had the same problem/symptoms for ~2 months

I changed the to NGK Iridium sparkplugs, New O2 and a bottle of Chervron Techtron and it never did it again.
Try this out...
Later,

[porschetub]

Originally Posted by Jrboulder

POP,

I thought the choke valve created a vacuum in the carb Venturi that richens the mixture? The AAV or the ICV allows more air to bypass the TB when the engine is cold. I thought that the DME controls the mixture and makes it rich when the temp sensor is reporting cold.

Jackson

Yes correct ,my sensor had an oxidized crud over it, a good clean with fine Scotchbrite and the ecu seemed to know the engine was" cold ",my start idle improved heaps.

[Jrboulder]

That's a good idea. I think I will pull my temp sensor and have a look.

That sensor might just be an item that should be replaced/ cleaned every 75,000 miles or so as a preventative measure.

[vwghia-guy]

Originally Posted by vwghia-guy

Well, the S2 is at the Porsche dealer while I'm in Utah for 3 weeks. Got a call from the Porsche tech and apparently he's re-verifying all the troubleshooting I had already done. Fortunately for me the car has the exact same symptoms with him - starts well, then starts missing after running about 30 seconds - and finally clears up after about 3 to 4 minutes. The miss so far has occurred across all cylinders. Something is causing the all of the injectors to dump fuel into the cylinders. BTW, fuel pressure was spot on and within specs after shutdown. He troubleshot the TPS, AFM, Air Temp Sensor, engine temp sensor, and o/2 sensor and all are fine. He tends to think that a wire in the engine harness got broken/damaged during the head swap and is planning to ohm out all the wires in the engine harness.

I'll post more when I hear something.

chris

It wasn't the engine wiring harness. He also replaced the reference(aka speed) sensor and the fule pump check valve. It wasn't either of those. He's sent the injectors out to be checked/rebuilt. And the saga continues..........

[Jcheevers]

Gentlemen the problem starts at the temp sensor change it, it will help, also look a frwilk.com web site something to do with the shudder fix code early 944, on his web site look for 944.com

[vwghia-guy]

Originally Posted by vwghia-guy

It wasn't the engine wiring harness. He also replaced the reference(aka speed) sensor and the fule pump check valve. It wasn't either of those. He's sent the injectors out to be checked/rebuilt. And the saga continues..........

Well, after extensive troubleshooting, this ?ucking problem still exists. So far...
Cylinder head was replaced with a rebuilt unit from Rennbay.
Engine temp sensor was replaced.
Speed(or reference sensor) was replaced.
Hall sensor in the distributor was replaced.
Spark plugs were replaced with correct Bosch units.
Plug wires ohm'd correctly.
AFM was checked to include the air temp sensor inside it and it's o.k.
Idle Stabilizer Valve was replaced with a new one.
All four fuel injectors were replaced with rebuilt ones.
Fuel pump check valve was replaced.
Fuel pressure regulator was replaced with new one.
Fuel pressure damper was replaced with new one.
The engine computer (ECM) was replaced with a know good one.
Compression check and leakdown were good.

I have followed every troubleshooting procedure in the factory manuals to the best of my abilities. I then took it to a competent mechanic who did the same. He's just as baffled as am I.
Is there anything I'm missing here - other than a for sale sign or a pound or two of C4? The only thing I haven't replaced is the engine wiring harness (because it ohms correctly). Plus, it seems that 1989S2 is one year only so I probably won't have an easy time finding one.
Any S2 owners in the Huntsville, AL area?

[djnolan]

Originally Posted by vwghia-guy

...the car has the exact same symptoms with him - starts well, then starts missing after running about 30 seconds - and finally clears up after about 3 to 4 minutes.

WOW Did you ever get this problem solved? I have almost the same symptom on my 85.5 (Rouge MAF'd or not) however it only happens on colder mornings, other times it is fine...

Since there is no OBD-2, this is where one of the old fashioned engine analyzers scopes would be helpful to run a power balance test and check the tailpipe emissions.

If it happened every time...

[Tom944]

Sounds like the heater in the O2 sensor has failed. Initial 30 seconds is open loop then it requires the heater until the sensor warms up. Once warm the heater is not required. Change the O2 sensor.

[Jfrahm]

It's easy enough to pull spark plug wires to see if it runs "less worse" with one particular cylinder deactivated. You can also use a temp gun to see if one plug or exhaust port is cooler than the rest after it has run badly for a good while. Checking plugs after it's been idling poorly can also tell you a lot.

Then go from there. Injector, intake gasket, vacuum leaks, etc. Since the 944 engine is batch fire it'll compensate for one bad injector pretty well though.