richie2

My 1990 Carrera 4 tends to die on me at tickover, especially when cold, but more lately even if warmed up.

New to 911 maintenance, any clues?

Also my nearest 911 specialist is a fair few miles away, is this a p[roblem a competent mechanic could look at nearer home?

Rich

garrett376

"Tick over"? I think you mean starting, right?!

Could be: cylinder heat temp sensor stuck or gone bad (check the resistance at various temps as described in Adrian's book), dirty idle solenoid valve (clean!). Try your backup DME relay (which you ought to have if you don't have one).

Those are some things you can do to rule out some possible cuplrits!

bhensarl

As Garrett's suggested, cleaning the ISV (Idle Stabilizer Valve) is just about as straightforward as 964 DIY gets. Even I did it successfully. Just use the "Search this Forum" link on the main page to search for "Cleaning the ISV". You should find all sorts of great info for that one.
Oh, and if you don't already have Adrian's book, go get it. It seems every week there's a thread extolling its virtues. Once again, a search will show you what I mean.
Welcome to the board!

Brian

bhensarl

For instance,
https://rennlist.com/forums/showthre...t=cleaning+ISV
Check this one out.
Brian

richie2

Thanks, will try that this weekend....
Rich

gjvander

Mine did the same. Problem went away after I replaced the oxygen sensor. Maybe try to meter yours first before you replace it. Also, get it from Pelican or some online parts dealer. I paid $180 for mine, and I think you can get them for $120.

Geo

Julian Thompson

Where will I find the DME relay on my Carrera RS as mine is doing this as well!!

Andy Roe

Julian,

Front fuse box, I think it's relay R41. The lable inside the lid should confirm this!

Andy

Julian Thompson

Thanks for this! Is it possible for the DME relay to be knackered and the car still drive?

Farp

Do you mean it's an intermittent problem or you can drive but have some symptom that you think might be due to a failed DME relay? Of course the relay could have an intermittent problem brought on by heat or vibration - that's quite possible. You can check by "jumpering" the DME relay. If the problem goes away it could well be due to the DME relay... But it could also be due to some other sensor causing the DME to stop the fuel pump. In my case it was a result of a failure in the airflow meter connector IIRC which meant the DME thought there was no air flow to the engine so it stopped the fuel pump. At least that's my understanding and it seemed to make sense at the time...

Julian Thompson

Sorry I think I have explained badly what the fault is on my car.

It runs fine when warm and starts perfectly but unless I use the accelerator to add additional throttle opening when it is stone cold it will not idle.

Once it is warm it runs and idles fine but occasionally dies at traffic lights and this aspect of it has got worse over time.

My understanding of it was that the DME relay controls the fuel pump which obviously must be working but additionally it appears to control the heating of the oxygen sensor in the exhaust; this would perhaps explain the cold problem if the heating circuit was out but of course some people run with no oxygen sensor (don't they?) so if this is the problem how do they get away with it. Additionally I always thought that the Lambda probe only has about 8% mixture control effect on most cars and so bearing in mind the huge need for fuel when cold I can't see Porsche making the warm up sequence rely on this.

Any thoughts?

DaveK

The DME relay doesn't have anything to do with the heating of the O2 sensor. The O2 sensor is ignored from stone cold - usually takes about 90s to be warm enough to be used I think. In fact - the fact that you have this problem immediately from a stone cold start proves it definitely isn't your O2 sensor that's the problem.

If people remove the O2 sensor the DME is told it's not there anymore. It may affect the mixture but certainly not enough to cause your problems.

The problem cannot be the DME relay or you would have problems when the car is running as well (not just idling).

When you say it occasionally stalls when warm (and always when stone cold) you don't mention idle hunting. So I guess that rules out some possibilities.

When you say it idles fine when warm - at what idle speed?

The first things I would check are :

1) Is your idle microswitch engaging? This is easy to check - open the engine lid (engine not running). Find the throttle linkage (i.e. where the throttle cable ends) and push the linkage slightly. You should hear a slight "click" as the idle microswitch is released (you should also see the microswitch just below the linkage). That doesn't prove it works - but it at least proves it's being engaged.
2) Clean the ISV
3) Clean the airflow sensor
4) Check your engine temp. sensor

Julian Thompson

Dave

Thanks for this help. The car does hunt when cold at idle. Does this change your opinion?

The idle microswitch is engaging. I will test to see if it is actually working with a meter.

I have cleaned the ISV which actually was spotless (car done only 25000 miles).

I think the engine temp sensor looks like best bet then. Anyone have any ideas what values I might expect from this sensor?

gilessav

check the airflow sensor and its connector. I assume the airflow sensor tracks are clear and not coated in oil deposited from overfill or over-oiled K&N filter or other. My car used to hunt on idle both hot or cold randomly with occassional powerloss and stall at lights and after a 24k service and investigation both the newly replaced O2 sensor and Airflow sensor were logging faults. Cleaned up Airflow connector, readings back in range and no probs since. Faulty Airflow connector was probably responsible for O2 logging fault apparently. Just a thought which is cheap and may help. Specialist said he's seen a few with the airflow connector as the issue. Failing that engine head temp sensor, flywheel speed ref sensor? I had new dist caps and rotors also as were original on 80k car. Plug wire arching may also play havoc?

Hope you find the faults as its really frustrating, beleive me i know
cheers
Giles.

garrett376

Test your cylinder head temp sensor if you have not already! This is an exact symptom of a stuck or dead sensor.