rough idle when cold

e_nough · 08-13-2001, 08:11 PM

hi, my 87 944na idles rough for the first minute after starting from cold. it also has no power and the engine sputters and acts like it is going to die.

no problems starting ever!

no problems after the first minute.

my mechanic says that the O2 sensor doesnot kick on until after about a minute or two, so im pretty sure thats not it. and i bet i could unplug it and it would still do it.

any thoughts.

thanks

T86951 · 08-13-2001, 09:08 PM

I am having a problem of rough low idle on cold starts on my '86 NA 944 and suspected the idle control valve and was about to replace it. that would have been a lot of work and about $120 wasted.
What I have found with a lot of sudying and testing is this:
The idle control valve on my car ('86 na) has 3 posts. On a cold start voltage is suppost to be supplied to the center and top posts which opens the valve to let extra air in to help it idle when cold. As the car warms up power is suppost to be shifted from the top post to the center and bottom posts which closes the valve.
Mine is always suppling power to the bottom 2 posts, cold or hot so the valve stays closed hence no extra air on a cold start hence an overrich (actually under supply of air) condition. I can unplug the connector and run 2 wires from my battery and touch them to the top 2 posts and the valve opens and it starts perfect when cold. I can then slide the connector back on after about 30 sec of warming up and it closes it and idles fine.
Now I have to figure out why my computer is not swiching power to the top 2 posts when cold. I have already replced the temp sensor with a new one.
I assume there is a relay somewhere that swiches this but I have no idea where so I am now at a dead end. I think we have the same problem as do others with a 85.5 and newer 944.

[This message has been edited by T86951 (edited 08-13-2001).]

[This message has been edited by T86951 (edited 08-13-2001).]

e_nough · 08-14-2001, 06:13 PM

do you have problems starting?

mine always starts first crank, no problems.

T86951 · 08-14-2001, 06:33 PM

never a starting problem. Hits and starts first thing cold or hot. and as soon as it starts when cold slow idle trys to quite ,I give it some gas and get a little black smoke and then clears out in 30 secs and is ok.
If the injectors were leaking off it would be flooded and would be hard to start. Not that here.

[This message has been edited by T86951 (edited 08-14-2001).]

kanaka · 08-15-2001, 09:26 AM

where is the temp sensor?

where is the plug you are referring to?

T86951 · 08-15-2001, 07:56 PM

temp sensor is on the side of the head or block , don't remember which but just under the throttle body. It has a connecter plugged on it.

Scott R · Scott R's Garage

Dirty mas air flow assy. will do the same thing, initial idle mixture is off and until the warmup sequence is done your idle is rough. As soon as the O2 sensor starts sending info the mix leans out and the condition stops. This is also sometimes the cause of hard starts when the enigine is hot. Just another avenue for you to try.

T86951 · 08-16-2001, 06:45 PM

Thanks for the info. But the thing I don't understand from that is my car starts first hit cold or hot and the voltage doesn't switch to the other post on the idle control valve. I have even thought about putting a pre 85.5 valve , 2 wire and 2 post that I think closes when it warms up. I don't have an answer to this but thanks for providing input on our problem. I know somebody somewhere has figured this out and knows the answer. One thing it never seams to happen with a pre 85.5 model.

kanaka · 08-20-2001, 05:59 AM

dirty? like nasty gunked up sludge or like just a little bit of dust under the black plastic cover can screw things up?

P944GUY · P944GUY's Garage

Your idle regulator could be carboned up and causing the valve not to open. Also, if your idle seems to surge back and forth a few hundred rpms then most likely your idle regulator. Have you had your CO and mixture adjusted by a mechanic with a computer?? They will check the O2 sensor as well, to see if it operating correctly. The idle reg is a fairly $ fix as you have to remove intake manifold around $300 part is around $125, labor about 2.5 hours. Have all vac hoses changed while the intake is off

markt944 · 11-19-2007, 10:03 AM

Anybody tell me how the cold start side of things works on an S2? what does what and were it is

After cureing hesitation {throttle switch} twice in the last week i have started it up from cold and it was runnin on 3 cylinders smokeing like hell overrich. After a couple of minutes it clears

Anybody any ideas?

Thanks mark

jlorda · 11-19-2007, 11:14 AM

My 87 924s with a 86 engine in it has the same problem. After about 5 minutes the car begins to idle smoothly. I guess the easiest solution is to just let the stupid vehicle warm up.

Aufgeladen944 · 11-19-2007, 06:26 PM

Yeah it's a twenty year old car. It has some idiosyncrasies that you need to just live with imo.

I just let the car warm up for a couple of minutes. I don't want to stress the manifold anyways. Plus, it goes away soon for hibernation

vwghia-guy · 11-06-2011, 04:57 PM

Did you ever get this problem solved? My 89 S2 is doing the same thing. I've done extensive troubleshooting but still no answers.

Help!

Quote:

Originally Posted by markt944

Anybody tell me how the cold start side of things works on an S2? what does what and were it is

After cureing hesitation {throttle switch} twice in the last week i have started it up from cold and it was runnin on 3 cylinders smokeing like hell overrich. After a couple of minutes it clears

Anybody any ideas?

Thanks mark

Jrboulder · 11-06-2011, 05:11 PM

My S2 does the same thing. Oh well.

Guest765 · 11-06-2011, 06:19 PM

Bad Dme temp sensor will cause this if its always reporting a hot engine to the dme (ie sensor stuck/bad)

Porsche-O-Phile · Porsche-O-Phile's Garage

T86951 I think you have your explanation backwards. Most engines need a richer than stoich mixture when cold (less air) and then more air (lower A:F ratio) once at operating temperature. Unless the 944 idle air valve works differently than a standard choke valve, it sounds like yours might be closed all the time (rich condition all the time).

Jrboulder · 11-07-2011, 09:25 AM

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

vwghia-guy · 11-08-2011, 06:39 AM

Got a new fuel pressure regulator and pressure damper coming. Will post if it makes any positive changes.

wild man · 02:18 PM

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.