Slow to return to normal Idle

[RNajarian]

Interesting Situation;

My Car has a 1983 SC Motor.

When I start it up it runs normally. When I rev it up to 4000 RPM it will return to normal idle 850.

HOWEVER after it warms up things change.
I will rev it up to 4000 and it will hold there for 5 seconds then SLOWLY return to idle, this time 1200.

At first I thought it could be a sticking accelerator cable but I've ruled that one out. Now I'm thinking it has something to do with the warm engine.

A good pal who knows 911 motors very well suggested it could be the spark distributor weights hanging up.

Any thoughts?

[crustychief]

Unplug the vacuum line from the decel air valve and see if the problem changes. Is your cat still in place with the 02 sensor hooked up?

[RNajarian]

No O2 sensor. The "brain" and 02 sensor were bypassed. My friend who did the engine drop bypassed this system.

I removed the vacuum line from the decel valve (the silver saucer shaped thing) and did not notice any difference

[James Brown]

The hack bypass might be the problem. You might have disconnected the electrical wires but the system might still be working in "limp" mode. And there could be several vacuum leaks going on.

[RNajarian]

It might be the problem. He got direction from fellow racers who have done it in their track cars.

The one thing that stands out to me is that it only happens when warm. That cannot be a coincidence