idle bouncing sporatically-need help!

[R22tech]

This was posted on Rennlist and is exactly what my car is doing, except my engine hasn't been rebuilt.

"So I'd like some opinions on this idle surging issue I've been having with my '84 3.2L since my top-end rebuild. Here are the things that have been done to the engine:
* all valves & rocker arms replaced w/ new
* cams reground to "C2" spec by Elgin
* heads mildly ported - "just cleaned up"
* cat bypass
* B&B sport muffler
* K&N cone filter & intake adapter
* clutch replaced with (much lighter) Sachs Aluminum.

I have NOT yet replaced the chip.

The engine is fabulously revvy. I especially love the way it pulls after 4K - feels like a turbo. The problem is that whenever I return to idle, like when I've slowed to stop at an intersection, the idle almost always bounces a few times before settling. It bounces back & forth between 800 and approx. 1200 rpm. Maybe 1.5 bounces per second, if you can picture that. It doesn't always do it, but when it does, it'll bounce anywhere from 1 to 10 times before settling down. Sometimes, especially after a high-rpm/high speed run, it'll just bounce itself silly until I intervene with ever-so-slight pressure on the throttle. Obviously, it's annoying.

I've been thinking it was because I'd installed the lightened clutch without changing the chip.. that the engine is coming down off of revs more quickly than the chip is programmed to expect, so it intervenes, thus bounce. But if that were the case, wouldn't the severity of the bouncing be more consistent? Why would it go nuts after high speed runs? These questions are leading me to think maybe it's the idle speed regulator unit. But if that were the case, why would this problem have come up only after the rebuild and all these other mods?

I don't really understand how the idle speed thingy works. But it could have been screwed up beforehand without exhibiting this bouncing because before the rebuild I had some serious intake leaks, and settings and the way things were working were much different. For example, the idle speed screw was out way further then to get 800 rpm idle.

Anyway, I'm wondering if anyone thinks for sure it's the idle speed regulator. If so, I may swap it out this weekend. If not, maybe I'll just wait until I get a custom chip (which is inevitable, just too costly to do now), see if that fixes the problem, and if not then start messing with the idle stuff.

Thanks in advance!

--------------------

Hugh
'84 Carrera "

I have messed around with the idle screw and just when I think the bouncing idle is gone-it comes back! Can anyone suggest a starting point, as far as how many turns, to set the idle screw? Or if you have the answer to Hugh's question- please post it. Thanks

[nhromyak]

I think this indicates a too low idle speed on the DME cars.

Could also be a dirty (oil) ISV.

Could also be a "lazy" O2 sensor. I have not really found too much to suppor this on the Porsches though.

Lastly, it could be running too lean.

Mine did this once or twice. I think I brough the Idle speed up just a hair. I have not seen this issue since.

Good Luck