apo128

Hi,

My dad has a 1998 993 C2S. The car is all stock.

If the car sits for a week or so, with the first cold start the engine ignites but it stumbles and it lugs. As a result, one of three things occurs, 1) sometimes it will smooth out and start; 2) sometimes it stalls; or 3) he turns it off and waits about 10 seconds. If you turn the engine off and wait for a few seconds it fires up immediately like nothing was ever wrong.

It will continue to operate perfectly day after day but if it sits a few days or more the same cold start problem occurs. If gas stabilizer is put in when stumbling begins to occur within 1 or 2 cold starts the problem disappears for a while then comes back after a tank or two of gas. When he stores it for the winter it is done so with gas stabilizer and always starts up immediately the very first start out of storage.

This problem has been going on for 4 or 5 years. Has anyone else had this problem or heard of it? Suggestions are much appreciated.

Thanks.

Stewart

Could well be a clogged Idle Stabilizer Valve (or Idle Control Valve as it's also referred to). It's the metal coloured canister that sits on top of the motor with pipes running from it. It's a common cause of lumpy running and poor starting. They get clogged over the years with 'soot' which stops the valve inside operating properly. It's a relatively simple job to remove and clean. Do a search on 'ISV' and you'll come up with plenty of hints.
Otherwise it could be a faulty DME relay - the one that controls the engine management - it's a cheap part, again easy to source and replace. 993 owners often carry a spare as they are a known failure, especially if they are the older part with the part number beginning '944' rather than '993' .

berni29

Hi

I agree with the above. The ISV is easy to remove, and there are how to clean an ISV guides on the internet. Definately try that.

Berni

apo128

Thanks for the suggestions. I will reccomend that he looks into this.

IXLR8

The ISV is best cleaned with lacquer thinner and a small 1/2" paint brush and Q-tips.

Hold the ISV vertically with the electrics at the top and go at it. After I was done, the ISV looked as if it had just came out of the package.

If it is the DME relay, just resoldering the board contacts will fix the issue. Keep a spare on hand as well.

No HTwo O

Is maintenance up to date on items like your spark plugs and fuel filter?

I'd also run some Techron Fuel System Cleaner through the system prior to your next scheduled oil change.

apo128

Thanks everyone. I have relayed this info to him. He is very religious about his maitanence -- both scheduled and unscheduled.

TMc993

If the suggestions above don't work, you may want to check the fuel pump. I remember someone referring to a check valve in the fuel pump that, if it fails, can leak down when a car sits for a period of time. If I remember correctly, start-up after sitting is made difficult because the fuel pump has to re-pressurize the injectors before the engine will start.

Good luck...

Terry