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Join Date: Aug 2004
Location: Charlotte, NC
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Angry Check engine light upon startup and rough running idle

I've been lurking here for quite some time but never had a chance to register or post. In any case my apologies for those who are also members of Rennlist but I didn't get my question answered there so I thought I'd try here:

I'm running into an issue where whenever I start the car up (it doesn't matter whether it is morning or afternoon, it happens probably 90% of the time) the car's "Check Engine" light is on and it runs really rough stumbling from about 100 RPM - 1000 RPM. The exhaust smells rich and the idle just hunts from high to low. If I let it go for a while it eventually dies and I have to restart it.

Normally to get past the problem I let it idle for a couple of seconds and keep my foot lightly pressing the accelerator so that it stays at about 1000 RPM. After making sure the engine has enough oil running through the system I rev the car up to about 3000 - 4000 RPM a few times and the check engine light goes away. So at this point the car is usually running as it should and I have no problems.

Occasionally however the car will revert back to it's "Check Engine" status after I slow down at a stoplight. Here's where it gets dangerous because I can't really accelerate as I should with the car in this condition.

I checked Clark's Garage site and did the "test" to determine if my FPR was bad The test came out as positive so I replaced the fuel pressure regulator and also replaced the DME relay. After the repair the can ran great for the first day or so - then it went back to it's old ways.

So let's assume that the two replaced parts are out of the picture. I also checked all the O-rings on the injectors when I removed them and the car had it's plugs changed about a year ago. I don't think it's the gas being used since the problem began when I lived in New Jersey and now continues in North Carolina.

The car is a 1991 944 S2 Cabriolet with about 116k miles on it. Does anyone here have any ideas what I should try next? Thanks in advance!
Old 08-13-2004, 06:04 AM
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suck my tail pipe
 
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shoot it and hang it's head on a wall in your den.
Or have it stuffed.
J/K
May be a number of things, what have you tried as a remedy so far?
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My car is naughty
Old 08-13-2004, 06:28 AM
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Frank B - I wouldn't mind doing that but the trophy wall is getting pretty full these days!!!

So far what I've done (aside from getting mad at my car) is to re-groove the AFM, use Techron fuel injector cleaner, check vacuum connections, inspect injector o-rings, replace fuel pressure regulator, and replace DME relay. What next???
Old 08-13-2004, 06:47 AM
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Are you using the correct octane fuel?
I know it's a daft question (a bit like have you turned it on?!) but if it's running rich... it could be because it's running rich that you're having trouble -
You could try adjusting the mixture with the hex bolt adjustr...
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(x)'89 944 S2 Cabriolet (Guards Orange) :
( )'90 944 S2 (Maraschino Dead!) :
( )'89 Audi 90 Quattro 2.3 20V :
( )'92 Renault Clio 1.4 :

*
Old 08-13-2004, 06:57 AM
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I always use at least 91 octane - some places have 93 and if so I'll use that instead. I'm not very particular about which brand, I just make sure it's something reputable so I doubt the gas I use is an issue.

As far as modifying the mixture - isn't this something that is adjusted automatically by the DME? Wouldn't adjusting this mixture without the proper instrumentation lead to possibly severe consequences?
Old 08-16-2004, 04:48 AM
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My S2 was running rich and after a service still had this problem with Check engine light. The oil pressure would drop to below 1 when I came to a stop at lights. I ran the engine really hot for a couple of hours on a loong journey and now the oil pressure only drops as low as 2 at idle. Could be some old sludgy oil in the galleries, try an engine flush and oil change (do the filter too - use genuine porsche filter!). Won't hurt, simple to do and may fix this problem.
You will need to go to a garage to check the emissions levels and you can adjust the mixture as it's on the machine.

This is an easy way to see if this is the problem but it may be more complex: i.e. some of the fuel injectors are running rich while some are not rich enough, an emmissions test can only give an overall reading...

You can add a little more air to the mixture (using hex bolt on airflow box) - this has the meter which tells the DME you are getting enough air when in fact you are not (because of this adjustment!) If it's running rich, this adjustment may have slipped, although some garages make older cars run rich to disguise other problems.

In summary I would say you need to get your mixture even, then address the oil pressure issue...
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(x)'89 944 S2 Cabriolet (Guards Orange) :
( )'90 944 S2 (Maraschino Dead!) :
( )'89 Audi 90 Quattro 2.3 20V :
( )'92 Renault Clio 1.4 :

*
Old 08-18-2004, 02:54 AM
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