Fluctutating rpms on start

[Rosemary Sheel]

Your website has already helped me with my 83 Porsche SC After my mechanic put in a new accumulator, it began to start reliably.

The car starts, I drive it 5 miles. Park. Later when I start it again, the rpms begin to fluctuate from 0 to 1700. And then stalls. I’ve got to gun it to get it out of the parking place but then after driving a bit the rpms are normal.

Here’s what has been done to my car recently.
August 2011; new fuel pump
January 2012: repair fuel pump power
Bypass fuse panel and repair wiring
July 2013 replace coil, distributor camp roto, adj. timing and fuel injection
August 2013 New battery
Jan 2014 replace spark plugs
Adjust fuel injection
Adjust timing
Aug 2014 Replace Fuel Panel
New Battery
New starter
Fuel pump relay

August 2014 replace accumulator

Can you give me any advice?

[DRACO A5OG]

You seem to have a massive vacuum leak. Other CIS will chime in, I'm sure.

[Rosemary Sheel]

Hi, Draco.

Thanks for the advice. I had gotten the idea of a vacuum leak from reading these posts. Now to tell the mechanic that I think I have a "massive " vacuum leak. Yikes.

Best regards,
Rosemary

[lsf911]

Did the car have this problem before you started all this work? Were the injectors pulled? If so, did your mechanic replace the o-rings?

I agree with Draco, sounds like a vacuum leak. My car does the same thing but not quite the fluctuation you have in rpm's. Wants to stall after warm restart but only for a few minutes then evens out. I have not found the culprit yet.

[Rosemary Sheel]

Hi, Lou,
Thanks for your answer. My problems began when my Cliff alarm system burned out. I had another alarm installed despite my mechanic's advice to just forget about it. That began a series of not starting, sometimes when hot, sometimes when cold. Also, it had no pep. After he fixed the spark plugs it seemed to run well, but then began the starting problem. Once in bumper to bumper traffic, it just stopped. It wasn't too hot.

Now with new starter, accumulator, etc. it starts but I have the feeling that it isn't running smoothly although the gauges show nothing. I don't think it has the power it used to.

Since I know nothing about the engine, I can only describe things in this way...my car isn't happy!

I'll ask him about the O-rings...need to look that up...But it's a good question.

Thanks for your help.

Rosemary

[Targalid]

You have replaced many components. I am not sure what "replacing the fuel panel" means. The fluctuating idle at start up is usually a sign of a too rich mixture. Why would this be? On cold start, the WUR (warm up regulator, the fuel pressure regulator) keeps the fuel pressure low to assure a rich mixture during engine warm up. As the engine warms, the WUR raises the fuel pressure which leans the mixture. It sounds to me like your WUR is not acting correctly. If this is a new problem, perhaps an electrical connector is not properly attached or a vacuum line has come loose from the WUR? Since this problem began with another electrical problem, I suspect that a fuse, a wire, or some other connection is at fault which controls your fuel pressure, keeping it too low and thus too rich for a warm start. These kinds of problems can be diagnosed using a fuel pressure gauge.

[Rosemary Sheel]

Hi, Targalid,

I meant to write fuse panel or fuse box. Being ignorant of all this I misspoke. Some fuses (there are these little brass bridges) had burned out. And the entire fuse panel/box was replaced. I have replaced a lot of parts. All were genuine Porsche parts btw.

The rpms on a cold start are usually 1700. Then drop to 7000 once it is warmed up.

Good to know a gauge can diagnosis this. I'm taking the car over on Tuesday. I'll let you guys know what happens...hope I can tell you that you've solved my problem.

Regards,
Rosemary

[Rosemary Sheel]

I told my mechanic what I learned from you guys. He was interested and from your input got the idea that maybe I needed a new oxygen sensor. He replaced that, checked the hoses and replaced the connections.

Now the car runs perfectly. Good start, good power. Like new.

Thanks for the input.

Rosemary