High idle cause

KDXrider · 01-13-2009, 09:18 PM

My early 944 idles around 1200 - 1400 when warm which I know isn't right. I just ordered a vacuum hose kit form LR but I'm wondering if there are any other possible causes of this. Any input would be greatly appreciated.

Thanks,
Kevin

Outback Porsche · 10:32 PM

[edit]

You've probably got a bad AAV and the TB has been adjusted (both the bypass screw and throttle screw) to compensate - result is high idle when warm. Bad vac hoses don't help.

Clean your TB out, replace the vac hoses, check your AAV and replace if necessary, adjust your TPS, put it all back together and adjust your idle.

Cheers

bearone2 · 01-14-2009, 08:18 AM

see if the throttle cable is too tight.

Zero10 · 01-14-2009, 08:25 AM

^^^
Such a simple thing but this can be your issue too. There should be just a hair of slack in the cable, and if you push it down it should move just a little bit before you hear the TPS click.

KDXrider · 01-14-2009, 02:38 PM

Throttle cable has just a bit of slack in it so it can't be that.
Will be checking AAV , TB, and TPS this weekend.

Also, I forgot to mention that it idles around 800-900 when cold then the idle rises as it gets warmer.

Thanks for your help,
Kevin

Born2bwild1191 · 01-14-2009, 03:55 PM

Mine does something similar...After its really warm (driving for 20+ minutes) it will decide to idle at around 2100 RPM at red lgihts and such...but if it's a long light, sometimes after about 30 seconds it wil just go back to normal, and sometimes it doesn't idle high at all...a rather strange thing. When it finally does decide to come down to normal idle, it comes down very slowly.

CJFusco · CJFusco's Garage

Mine does the same as Born2bwild, especially when it is very hot out. I posted here on the board about it a few times, but nobody seemed to know the problem.

Outback Porsche · 01-14-2009, 11:11 PM

Born2/CJ

Give the TB a real good clean out with carbi cleaner. The butterfly could be staying a little open.

Cheers

Dark Skies · 05:28 AM

This won't be the cause in every case but it's worth checking out if the problem has been with you since you bought the car because you don't know what the PO got up to.

Sometimes the idle starts to stumble, get lumpy and generally is very low due to a poor earth between engine and firewall. If the strap or the mountings at the back of the engine get corroded the strain on the car's system drags the idle low - especially when cold. So a lot of owners, instead of getting to the bottom of the problem, tweak the idle to compensate (using the screw on the TB). Sometimes this 'fixes' the symptoms. Sometimes it just fixes the from cold idle problem but causes a higher idling problem when everything is warmed up and there is less of a demand on the car's electrical system.

To check if your idle might have been tweaked because of the above try starting the car from cold, let it idle and then get a booster cable and clamp one end to a good earth on the engine and the other to either a good earth on the chassis or directly to the negative of the battery (easier if the battery is mounted under the hood). If your idle significantly rises then you know the earth strap needs some attention and that the previous owner may have tweaked the idle. Sort out the earth and see if the idle has improved. If it's now over the spec at cold then you can bring it down to the correct rpm and hopefully see a reduction when hot.

SPCC · 04-20-2017, 02:09 AM

Quote:

Originally Posted by Dark Skies

This won't be the cause in every case but it's worth checking out if the problem has been with you since you bought the car because you don't know what the PO got up to.

Sometimes the idle starts to stumble, get lumpy and generally is very low due to a poor earth between engine and firewall. If the strap or the mountings at the back of the engine get corroded the strain on the car's system drags the idle low - especially when cold. So a lot of owners, instead of getting to the bottom of the problem, tweak the idle to compensate (using the screw on the TB). Sometimes this 'fixes' the symptoms. Sometimes it just fixes the from cold idle problem but causes a higher idling problem when everything is warmed up and there is less of a demand on the car's electrical system.

To check if your idle might have been tweaked because of the above try starting the car from cold, let it idle and then get a booster cable and clamp one end to a good earth on the engine and the other to either a good earth on the chassis or directly to the negative of the battery (easier if the battery is mounted under the hood). If your idle significantly rises then you know the earth strap needs some attention and that the previous owner may have tweaked the idle. Sort out the earth and see if the idle has improved. If it's now over the spec at cold then you can bring it down to the correct rpm and hopefully see a reduction when hot.

This was great advice for the idle problem on one of our cars. www.SouthernPorscheClub.com