Idle ups and downs

[yondermtn]

I've been having fluctuating idle symptoms for a while now and I haven't been able to find the cause.

1977 FI 2.0
When I start cold the idle seems fine. There does not seem to be much noticeable difference once warmed up.

When I go to restart when the engine is already warm I get a fast idle. Sometimes the idle will return to normal after driving a bit, but not always.

If I turn the engine off again and restart right away the idle will usually slow(usually to slightly higher rpm than cold start, but still acceptable).

I have been checking for vacuum leaks and have changed a few vac hoses and the AAR elbow. If a vacuum leak is causing this, wouldn't the high idle come and go as the engine warms/cools regardless of starting/restarting?

My next step is to pull the AAR and shoot it with carb cleaner and test the ohms.

What else can I look at?

[Amskeptic]

I've been having fluctuating idle symptoms for a while now and I haven't been able to find the cause.

1977 FI 2.0
When I start cold the idle seems fine. There does not seem to be much noticeable difference once warmed up.

When I go to restart when the engine is already warm I get a fast idle. Sometimes the idle will return to normal after driving a bit, but not always.

If I turn the engine off again and restart right away the idle will usually slow(usually to slightly higher rpm than cold start, but still acceptable).

I have been checking for vacuum leaks and have changed a few vac hoses and the AAR elbow. If a vacuum leak is causing this, wouldn't the high idle come and go as the engine warms/cools regardless of starting/restarting?

My next step is to pull the AAR and shoot it with carb cleaner and test the ohms.

What else can I look at?

Ar you saying the idle speed is variable over the course of the day, or that it hunts in short cycles?
If hunting, it is usually a vacuum leak. Sometimes rich mixture compensating for a vacuum leak will cause lope.
Look at the wiper in the AFM as it is loping. Hold wiper at favorite spot. Does lope go away?
Colin

[yondermtn]

This symptom seems to come and go. I'm not getting the hunting or loping for an idle speed. It seems to go like this:

Start up cold: engine idle speed is good

Start up after driving: engine idles fast

Turn off and restart: engine idles good again


It just seems like when started hot, it wants to idle fast.
I'm still watching this symptom and will report back.

[dtrumbo]

Sticky distributor?

[yondermtn]

How does a distributor stick? And, how do I test this?

[dtrumbo]

It sticks because it's dirty and/or gummed up with grease and/or it's worn out. When you start the bus, the cold-start doodads make the engine idle high by design. Faster RPM means some advancing of the timing which is done by the distributor. If it's sticky, the timing never goes back to "normal" which may be causing your high idle. Turning the engine completely off allows the distributor to return to the "normal" position (complete absence of centrifugal force) until your RPM increases past the sticky point in the distributor. This would emulate the symptoms you have and the only reason I know this is I had the exact same problem in my fuel injected Beetle.

How do you test? I don't know other than by swapping distributors with a known good one. The way I found my problem was the sticky distributor in my bug wasn't the "correct" one for the car. I bought a used "correct" distributor, had it rebuilt by Philbin in Portland, OR, installed it and my problems vanished. I would see if someone can loan you a known-good distributor to test with and then if that proves to be the problem, you can have yours rebuilt. Otherwise, you can have yours rebuilt on the hopes that cures the problem with the consolation that you'll at least have a nice good-as-new rebuilt distributor in your bus. Maybe others have a mo' bettah way to test than my shotgun approach.

[yondermtn]

Thank you.
This definitely sounds like something that could be causing my symptoms. I found this on that other site:

http://www.thesamba.com/vw/forum/viewto ... istributor

I will try the cleaning method in the above post. I also have another distributor ordered as a spare. I'm trying to get everything in tip top shape for a 1000mi+ trip next month.

[Randy in Maine]

If when the idle is fast upon a warm start, and you engage a little 1st gear to slow down the idle at a stop light, does it stay slowed down or go right back to 1200 RPMs at the next stop light?

[yondermtn]

It usually slows down. It doesn't slow down if I just bump the gas, but if I bump it under load it does usually slow down.

[dtrumbo]

Mine did as Randy describes. I could force the engine RPM down by slightly engaging first gear with my foot on the brake. That would reduce the centrifugal force enough for the distributor to find it's way back to "normal". However, once I increased engine RPM back above the sticky point in the distributor, the RPM would stay high again. Quite frustrating.

Here's my saga on TS. Thanks again to Randy In Maine for all the help.

http://www.thesamba.com/vw/forum/viewtopic.php?t=236257

[sgkent]

I would guess sticky dist weights, vac advance or sticky throttle body.

Start by putting five ir six drops of oil on the wick under the dist rotor. Put 1 drop of oil on each dist pivot. Put a drop of oil on pin that sticks up where the vac advance attaches too and a few drops where the black thing with a ball bearing under it holds the dist plate down.

I have also seen points sticky when cold and that will change dwell and timing. Put one drop of light sewing machine oil on the pivot for the points.

Note: you may be able to see the pivots for the weights by looking down into the dist plate and rotating the engine until they each pass by. A drop of sewing oil that weeps under the weights won't hurt any either.