Hot Start Problem and idle hunting
 

I'm stumped...will probably take the car to my local mechanic. I have a hot start and idle hunting problem. The cause of the hot start is not the fuel pump check valve or the accumulator. How do I know? I replaced them. The car runs and starts great when cold. When hot the car refuses to start and when I pull up to a stop light, etc. the idle plummets to 200 rpm then jumps back to 1200 rpm. Close to stalling the car. Very nerve racking when you know that if it stalls you probably won't get it started again. Do you think these two issues are related? Oh yea, when the oil cap is off, the car idles at 1000 rpm. If I rev the motor and release, the idle drops back to 1000 rpm. When I put the oil cap back on and rev the motor, the idle starts to hunt again. Very frustrating.
Bruce


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Bruce
1982 SC

Another possible is your electrical system. I developed hot start problems last year after having some work done, and it turned out that the shop hadn't reconnected the ground strap. Apparently, the electrical system is weaker when hot, so it only manifested itself then.

Emanuel

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Emanuel Brown
1983 911 SC Targa
http://home.att.net/~epbrown01/91183.jpg

I'd look at your warm up regulator or maybe your auxiliary air valve.I think the problems are related.My 83SC had similar problem,it was my warm up regulator.

The two most common maladies are a vacuum leak somewhere in the system, or too high a control pressure from the warm-up regulator. Another overlooked issue could be the mixture, or a faulty auxiliary air regulator that is not closing completely. Finally, a dirty sensor plate could also cause these kinds of problems.

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Michael
'78 911SC Euro

I think I've read some earlier posts with similar symptoms that ended up being an O2 sensor problem. Have you tried disconnecting the O2 sensor? Do a search on O2 sensor and see if you find something.

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Bill Krause
'79 911SC Euro

set the CO to 3.5% on an exhaust gas analyzer,the idle at 1000, the timing at 35 degrees total advance, and leave the oxygen sensor unplugged. see if that helps.

set the CO to 3.5% on an exhaust gas analyzer,the idle at 1000, the timing at 35 degrees total advance, and leave the oxygen sensor unplugged. see if that helps.

Start with disconnecting the O2 sensor.

Nick.

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Nick Shumaker
1982 911SC Coupe
nickshu@yahoo.com
PCA -- Rocky Mtn. Region

Thanks to everyone for the thoughts. I should have mentioned that I have the O2 sensor disconnected. I also had the top intake boot off recently and cleaned the intake plate of the grime build up. The plate seems to be free and adjusted to the right height. I'm also confident that the car is properly grounded because I attached the ground strap myself under the cooling shroud after a recent alternator rebuild. I guess I'm at the point where I think it is the warm up regulator. However, I'm tired of changing parts...so I'll reluctantly take the car to the shop tomorrow. I'm ready to drive it with no worries. Still a slight blow to the ego.
Bruce


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Bruce
1982 SC

One thing I forgot to mention is that too rich a mixture will cause this as well. Making adjustments per John Walker's instructions had my engine running like a sewing machine........

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Michael
'78 911SC Euro

Michael's got a good point about too rich a mixture. The fact that the car runs better with the oil cap off (it should run worse) suggests that your mixture is too rich. Rather than just handing the car over to your mechanic to start parts swapping. Have him set the mixture per John Walkers post at 3.5% CO. It shouldn't cost more than $30 to get 10 minutes time on an exhaust analyzer.



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Bill Krause
'79 911SC Euro

Got the call from the mechanic. Turns our I have a bad fuel pump. Putting out 3 bar. He says it should be 5. It was a rebuild. I'm buying a new one this time. Will get it back tomorrow and see how she runs. Thanks again.
Bruce


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Bruce
1982 SC

Can someone tell me how to adjust the mixture?...80 SC..

Can someone tell me how to adjust the mixture?...80 SC..

BTT

Just wanted to give you all the final word regarding my idle, hot start & vapor lock problem. It was my fuel pump. It was putting out enough pressure to open the injectors when the engine was cold. However, as the temperature increased, the pump was not able to keep up and thus, no spray out of the injectors. Dead engine. Got a new fuel pump installed and the car runs killer. Took it up into the mountains and did some twisty roads. Good fun. Thanks for everybody's help.
Bruce


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Bruce
1982 SC