911SC hunting at idle

[Cabdriver]

Hi everyone, and welcome to my first post. I've had my '83 SC cab for about 25 years and 150k miles. While I enjoy working on it for basic maintenance items, I usually have my mechanic work on items requiring gauges, tools, and expertise I'm lacking. So here's the problem:
Initially, the car started running rough and was hard starting when hot. My mechanic determined there were several vacuum leaks, and replaced a bunch of hoses and all fuel injector O rings - the old ones were dried and broken. The car runs fine now except that it now hunts about 50-100 rpm at idle. He adjusted the idle and mixture after replacing all parts. He did notice that the throttle position indicator (or maybe potentiometer) appears to be loose where attached at the throttle valve. He's reluctant to remove the valve because if it needs a bushing or other part, he may not be able to find it in stock anywhere. Would anyone know where I could pick up a used or rebuilt throttle valve? Is the TPI just bolted on or could there be a worn bushing on the valve itself causing the problem?

[gazzerr]

I'd smoke test it and look for more vacuum leaks first. How old is the airbox? After 30 years the glue gives up and they leak through the seam on the bottom half of the airbox. Other areas are the cork seal on the oil tank level sender and the vacuum pipe for the brake booster.

When it's running right the lamba system will very slighty hunt the rpm as it adjusts for stoich at idle.

I've seen rebuilt throttle valves available from all the big Porsche parts vendors. It shouldn't be hard to find but not cheap.

[al lkosmal]

Hunting at idle is a typical symptom of it being too rich. It is likely that with the air/vacuum leaks you had, the car was tuned very rich to compensate for the extra air.........Once your mechanic fixed the air leaks, it would then go rich and need to be adjusted to obtain the proper A/F mix. It may not be adjusted properly yet. It is best adjusted while monitoring with an A/F meter, like the Innovative LM1 or equiv....but can be done as follows;

CIS Idle Speed and Mixture Setting Without an Analyzer


regards,
al

[Cabdriver]

All good ideas, looks like I have still more checking to do. Thanks for the input!

[don gilbert]

On an 02 car you can use a dwell meter to get mixture rite. Best way.

[stlrj]

Originally Posted by Cabdriver

All good ideas, looks like I have still more checking to do. Thanks for the input!

Stop checking and start doing. We all know the classic signs of over-rich is a hunting idle, so please save us all some time and get out your allen and start leaning.

Whew!
Joe

[Cabdriver]

thanks to some great threads on idle mixture adjustment from other Pelicans, I was able to get it to idle right on the money. Thanks everyone for the help and saving me before I started chasing wild geese!

[stlrj]

Originally Posted by Cabdriver

... I was able to get it to idle right on the money. Thanks everyone for the help and saving me before I started chasing wild geese!

The suspense is killing me. How'd you fix it?

Joe