Idle Hunting Problem

[russell83]

I have a 1983 911SC Targa that is factory. I have had idle hunting problems come up on different occassions. The first would always hunt at idle, where a new O2 sensor solved the problem. The next time (most recent) I had a "fuel regulator" replaced, which seemed to fix the problem, but it has crept back in. The hunting idle does not occur when I first start the vehicle. It happen more when it's warm. The idle will fall to around 800-900 and then bounce a couple of times between those #'s and 1,000 and 1,200. The idle then settles sometimes at 950 where my mechanic tells me it has been set for or a little higher. Interestingly, when it gets into this hunting mode, I can seemingly break it out and return it to normal by turning the engine off and restarting it. Sometimes it takes a couple of times. We have looked for vacuum leaks and tightened down some of the intakes. I don't believe it's a vacuum issue, but that is just a hunch. I'm wondering whether it's the mixture or something else. Help, please.

[Al S]

Russell, try going leaner on the idle mixture..

[911 Rod]

Russell I have the same problem with my 86.
Is it intermittent as mine is?
I can't see making adjustments to a EFI for a periodic problem.
I've been battling this for a while.

[russell83]

Thanks guys for the quick reply.

Al I'll try the leaner mixture. 911 Rod mine is not exceptionally intermittent. It seems to get itself into this mode and doesn't come out until I shut down the car. The engine is running very strong...I've done all the maintenance recently, major tune up. Are these idle hunting problems common in 911's in these years? Thanks again!!!

[911 Rod]

Did you try bringing down the idle by letting out the clutch a little?
Works for mine and keeps the embarrassment to a minimum.

[russell83]

911 Rod I haven't tried that. The hunting problem isn't too bad, but something seems like it needs tweeked. Did you try any mixture changes?

[Mookster]

My 83SC had the same problem. Turned out to be all the fuel injectors were shot.

Replaced all the injectors and properly adjusted the A/F mixture and my idle problems were resolved.

Replace the O rings on each injector as well.

Have your shop adjust the mixture with a sniffer up the pipe. The readings can tell you a lot without throwing parts at the problem.

[russell83]

Mookster...thanks, I'm talking with my shop shortly.

[ruf-porsche]

Do a test on trhe AAR. It is suppose to be close once the engine starts. The electrical portion could be causing the problem.

[scottb]

I had the same problem on my 84, and it was intermittent. I had the mixture adjusted and the problem hasn't come back.

Get your mixture checked. It's an easy, inexpensive, possible solution to the problem.

Scott

[mkimber]

My hunting idle problem was caused by a split vacuum line. I replaced the hose, and the problem was solved. The hard part was finding the source of the problem because all conventional fixes didn't work.

[911 Rod]

Michael,
Was yours intermittent?
Did you just spray something flammable around the hoses to see if it effected the idle?
The reason I ask is that my car is fine if I leave the oil cap off (don't ask me how I know) and this leaves the air return line that attaches to the oil line open.
Rod

[ruf-porsche]

When an engine is cold extra air is needed to start and prevent the engine from stalling. That is the function of the AAR and AAV.

If the hunting goes away when you remove the oil cap that would suggest that your mixture is out of whack. The 02 sensor is trying to compensate for the mixture by varying the frequency valve, that is probably why it is hunting. You can test this by disconnecting the 02 sensor. If the hunting idle stop than the mixture is probably out of whack.

Bring it in and get the CO set correctly.

[stlrj]

On my 86, a slow hunt was caused by the mixture too rich and the fast idle hunt that sounded like a dog panting was caused by having the idle speed set too high.

Hope this helps.

Joe

[911 Rod]

Any idea why if I let the clutch slip a bit to bring the idle to normal it stays there?
Thanks
Rod

[mkimber]

Rod,

My hunting idle issue was intermittent. I didn't spray anything flammable to find the leak. It was a tedious process of testing, replacing, and visual inspections until we found the source of the problem. I have no definitive answers as to why your idle smooths out with the oil cap off or when you let the clutch out a bit, but Ruf-Porsche's answer makes sense to me.

[Chris_1983]

I'm having the same problem and letting the cluth out helps mine also.

[Nine9six]

From what I found in a search, the WUR may need replacing.

[ruf-porsche]

Before throwing a bunch of money on replacement parts, you need to determine the cause of the problem. If you suspect it's the WUR, then get a pressure gauge to verify the system pressure and control pressure. If the pressures are out of wack then consider replacing the WUR, but don't replace parts until you determine the cause of the problem.

[russell83]

Thanks to all for this great feedback! Any chance someone can give me what a few of the acronyms used are: AAR, AAV and WUR. Thanks again. Russell