Porsche-O-Phile

My '86 951 (the cursed one) has a new demon I have to exorcise - it won't idle. Here's the background:

I finally got it running last weekend and took it for a drive maybe for an hour and a half. All was well then until right when we got back to my place. I got out and opened up the garage door to let my wife drive it in as I guided (it's a bit tricky getting into due to alley obstacles). As she pulled in, I noticed a change in the idle from the normal smooth operation to a rough, choppy "surging" idle. The car stalled, she restarted it, pulled in, whereupon the car stalled again. I was like, WTF now? When I opened the hood, I noticed that the idle adjustment screw (on top of the throttle body) had backed out and was sitting on the intake. I put it back in and have played with all kinds of positions for it but I still can't get the car to idle smoothly. It's almost like the mixture is screwed up or something; it seems to be less of an idle speed issue than it is a roughness issue.

Once the engine builds up some RPM (if you put your foot on the gas a bit) it's fine above maybe 1,200 RPM or so - seems smooth and normal.

WTF is causing this?

hosrom_951

You said the screw was backed out? is this the new screw you posted a thread on earlier?

In either case (new or old screw), try applying just a DROP of loctite and put the screw back in and see if there is a difference......

951Porschiste

"The wife driving the car is the problem..." he said, ducking for the whack at the back of the head

Porsche-O-Phile

Haha. I already blamed her, not to worry.

Anyway, yea it's with either the new or old screw - doesn't matter. Screw position doesn't seem to affect it THAT much. Obviously if you put it all the way in it chokes off the air flow and the thing dies, but it runs really rough regardless of screw position. Clark's says this could be speed & reference sensors, engine temperature sensors, O2 sensor, etc. So darned near anything. I'm reeeeeeaallly getting frustrated with this car; I'm not looking forward to another three weekends wasted on chasing down THIS problem now. I still have yet to put 200 miles on this car or enjoy any boost at all on it. Just wondering if someone might know what to check first.

hosrom_951

First off, as usual, vacuum lines (Jeremy might kill me for saying this )......

Then start checking electrical stuff........

Porsche-O-Phile

Weird thing just happened - I drove it and it seems fine now.

951Porschiste

I told you it was the wife thing... ducking WMD from the wife!

Porsche-O-Phile

LOL. I think part of the problem might be the venturi hose. It is badly cracked and during the recent turbo replacement it split right down the side. I had to cut it (trim off the "split" part) and had begun developing a new split. I taped it off and it seems a lot better, though still not perfect. I have a replacement hose on order but a lot of those lines are old / brittle and will eventually need replacing - ditto the j-boot. It was probably a factor.

Now I gotta' find my boost!