During the very hot weather we've been having here in the UK recently, I have experienced my 1990 964 idling at very high revs after driving in heavy traffic for while. It rose to around 1500-1750 rpm at idle.

Has anyone else experienced this at all? Is it just a symptom of the extremely hot weather and cruelling along in heavy traffic - i.e. bad air flow?

The last couple of journies it hasn't repeated but I'm not convinced it's cured.

Any feedback/experience welcome.

 

Dear Alister,
Higher rpm requires more fuel and more air. I would suggest that your idle speed valve has a problem. It may be a massive engine overheat problem due to the weather and driving in the traffic. I would certainly monitor it but wait until it happens again and see what other things are going on around you like the engine temp where is it etc.
Ciao,
Adrian
964C4

 

Thanks Adrian. Thanks for the advice.
It definitely was hot but just over half way - not quite up to the second bar. In town the temp needle usually sticks at about halfway and on open road usually at the first bar level. I assume these temperatures are usual for an engine running normally?

 

You may want to consider removing your engine undertray.

 

I love this place!

 

Yep, the engine undertray is well known for causing high idles.

 

Cannot wait for the next edition of some of the Porsche related magazines.
Newly discovered 964 problem. "Rear engine cover causes high idle in hot weather". "Porsches sizzle with rear engine cover"
Oh by the way my colleague just turned up in his 993 C4 complaining of hunting idle when it is really hot like right now. I told him to remove his rear engine cover. I wish I could have photographed the look he gave me. I had to explain it all to him because he thought I was serious.
Ciao,
Adrian
964C4

 

How on earth would removing the undertray cure the problem? I'm baffled?

 

It's a joke - there is another thread on whether keeping your undertray on causes premature valve guide wear or not. It's a subject that has been around for a long time, and lots of people disagree on.

It can't be causing your idle problem.