3.2 idle unstability..

[Micker747]

Hi,

my 84 3.2 is running a bit low in idle, and also not very stabile.
Any good advice?? The idle valve is new!

-Mike

[DonMo]

Has it always been low or just recently? What RPM? Early 3.2' were set at 800 rpm, later at 880. Air leaks were notorous for changing idle. Easy to find with a can of intake cleaner.

[Micker747]

Hey don

i dont know how it has been before, i just fitted it in my '71! I think th idle is around 500rpm, it stops if i take off the oil tank cap.

-Mike

[Goth]

Hi Mike,

Have you already tried the idle adjustment on the throttle body?

Check this link to Steve Wong's 911chips website .

About half way down, it explains how to do the adjustment for the 3.2.

[wnsgc]

Interesting topic. My 85 Carrera idles at 650rpm, which its done since I bought it 3 months ago. It idles fine (not unstable), but it does seem low. I've also noticed that while accelerating, I hear a whining noise, almost like a turbo (which it is not!). More recently, since I've been driving with the top off and the window open, I've heard the faint noise of low back fires (not loud) when downshifting from 5->4, 4->3, 3->2.
Based upon what I've read, all of this ptoins to a vacuum/air leak somewhere.

DonMo's comment above about using intake cleaner to find a leak intrigues me. How do you actually find this type of leak with the cleaner?

[Goth]

For intake system leaks: Just spray some carb cleaner on the suspect vacuum leaks and listen for any change in idle speed. If the idle changes, you've found a vacuum leak.

Edit: A note of caution...Be careful not to spray on anything really hot like the exhaust system. Don't want to burn up the car!

As for small backfires under decel; if it's a rumble or burble sound, I think that may be normal. Bigger backfires could be a sign of an exhaust system leak (oxygen pulled in the leak & mixing with hot unburned full in the exhaust system ignites causing a backfire).

Hope this helps! :

[Nine9six]

A STEADY low idle does not sound like a vacuum leak. Try adjusting your idle per Goth's link to 911 chips.com and report your results if you need further assistance.

[wnsgc]

Thanks for the info. The noise I hear during downshift acceleration is more of a rumble/burble than an actual backfire. I'll check out the link listed above for adjusting the idle and will report back.

One more comment, I've noticed small cracks in the hose that leaves the upper neck of the oil filler, which travels around the back of the air box and attaches to the throttle body. The cracks are located in the first bend from the oil filler neck. Could this be a vacuum leak?

As an FYI, I cannot fine this hose as our host states its NLA.

[Micker747]

Thanks for the input guys.

I found a leak at the oil cap filler neck, i helped.
It runs perfectly smooth when cold, but when its warm its more unstable, like a typical older V8!! (where the car is rocking once in a while!!!).
There is no way on earth i can keep it running with the oil filler cap off, i don't know if it has anything to do with using a 1971 oil tank??

Mike