R.Pires

Hi all,

I’ve been experiencing some idle fluctuations on my 83S Euro 5spd.
It always starts at first turn of the key, whether cold or warm, when cold it stays at 1000rpm and when hot it stays at 750rpm.
That’s when it starts, because at normal running temperature every time I stop at a traffic sign or anywhere else, the idle it’s different, sometimes 1000, sometimes 750 and sometimes in the middle (800/900)!
I know I shouldn’t trust the tachometer but mine probably is more or less accurate because I can really hear the difference when it idles at 750 and at 1000.
Whether I drive around town, or highway or even I give it a little “push” at 5000 or 6000, when it stops the idle is always different, although it’s never above 1000.
When searching the Forum, I’ve found the possibility of a small (for now…) vacuum leak. Is that your opinion? If it is, this fluctuation will get worse, right? What else should I check?
Thanks in advance for your help.
Regards

WallyP

Carefully check the throttle (and cruise control if equipped) cable for sticking. Lube the cable ends and the quadrant at the front. Check the throttle pedal to make sure that it isn't hanging on the carpet. Check the air valve and throttle plate for sticking.

RedRose

I have the same problem on my 84 944. I am not sure if the Sharks have it, but there's an Idle Stabiliser Valve on the 944s. You might check for that.

Lizard928

on an euro 83 928S there isnt a stabilizer valve there is a AAV.

I would first check the cables as MrMerlin says, I would then look for vacuum leaks, and if both check out, then I would have the CIS system checked at a competant shop. It is possible that one of the componants is acting up.

John Struthers

Always good to look at the cables/quadrant.
In my case, 82 Weissach 4.5L opposed to your 4.7L -HP,HP, HP...envy-, I have the occasional high rpm idle. Strangely, only after topping off the gas in cool weather....?
However, I believe it's related to either the brake piston or vacuum booster as my brakes tend to get spongy/low pedal in cold weather as well. I have no visible system external fluid loss.
A little test for a general - or possible vacuum booster/brake piston - bleed off.
If you are stopped/parked when the Idle goes high on you pump the brakes if the idle changes look for connector leaks first to reduce the field of possibilities.
A good brake shop can isolate the problem fairly quick ask for a diagnostic fee schedule prior to work being done ...you are driving a Porsche and it's getting close to Xmas :<)
Good luck let us know the outcome.

R.Pires

Hi all,

First of all, thanks to everyone that answers, this is in fact a great Forum!
Sometimes we think we have a big problem and it turns out to be of simple solution.
Some WD40 in all the linkages of the cable, starting in the accelerator pedal, until the end of the cable and I have now a stable idle at around 800rpm!
Anyway, I noticed that one thing that may have contributed to this problem is that my engine is very very dirty; it probably hasn’t been washed not even once. It means 25 years without a bath!!!
I kwon that some people are completely against washing the engines, but I think mine really needs it. I won’t be doing it myself, I’ll leave the job for a specialized shop, that will make a professional wash and lubrication.
What is your opinion about engine washing?
Thanks again for the help.
Regards

John Struthers

That's good news.
Did you track the cables back to the firewall and lube as well?
And yes, your sHARk, after 25 years, is compareable to a gorgeous date in need of a little soap and water after horse-back riding all day - (uni-sex comment) -.