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914bob · Joined: 02 Feb 2008 Posts: 7 Location: Glasgow Scotland

Great knowledge on this forum guys - perhaps someone can give me a pointer on this one.

My car is a 1982 924 N/A, well looked after, what a lovely drive!

Anyway from a cold start, perfect 1000rpm idle settling down to 800 - run like that all day. If turned off and restart as hot engine - still drives nice but 400rpm lumpy idle.

What would cause this difference? Any adjustment ideas?

Cheers

Bob

Paul · Posted: Tue Feb 17, 2009 10:37 am Post subject:

If the lumpy idle only lasts a few minutes, you probably have early symptoms of the hot start issue that many CIS equipped cars have.

Do a search on "hot start". The issue may be vapor in the fuel lines.
_________________
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Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

A euro 82 is similar to the last cars we got here in the US.

Should have electronic ignition, breakerless distributor (not like earlier euro cars that got points, and had no cat), and electronic idle stabilization.

I would guess that the car is not set up properly (idle speed and mixture).

The late cars with the 3-way cats are different from earlier cars and you have to get the mixture and idle speed just right when the engine is warm, or it will never run correctly both when it's cold, and when it's hot (the engine that is). Idle and mixture can only be set after the valves are adjusted, the plugs are serviced, the ignition timing is correct, the vacuum leaks have been fixed, the engine is hot/worm, and the idle stabilization is disabled.

914bob · Joined: 02 Feb 2008 Posts: 7 Location: Glasgow Scotland

Thanks for your thoughts - much appreciated. Its not just a temporary drop in idle speed. more like the engine just has a different (lower) setting if it has not gone through the cold start proceedure. I could just wind the idle up a notch with the air bypass screw on the throttle body - but then it would be a bit too high when I'm driving after a cold start! Wonder if anyone ever had a similar experience.

Ozzie · Posted: Wed Feb 18, 2009 9:27 am Post subject:

You could have a stuck AAV.

Idle stabilsation? Not on my car.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

914bob · Joined: 02 Feb 2008 Posts: 7 Location: Glasgow Scotland

I appreciate that pointer from the other side of the world. Cheers Ozzie - I will investigate that one.

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

Where is the electronic ignition module on your car?

On the left front inner fender?

Is it a little silver or black module with a flat shaped plug?

Is there another black plastic box mounted ontop of it with two round plugs? If there is a black plastic box mounted above it, are there a couple of round plastic plugs laying there?

Ozzie · Posted: Thu Feb 19, 2009 9:34 pm Post subject:

I just have a silver box LH fender. flat plug (8 pin?).

Nothing else.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Boostsideways · Joined: 11 Feb 2009 Posts: 100 Location: CT, Southbury

My car does kinda the same thing.. well it used to. Now it just always seems to be idling a little strong 1.1k-1.3kish. it's alright tho i don't really notice any difference in anything besides if i dont throttle the gas on slight hills she'll die out.. But im pretty sure thats normal. I'd say just try turnin' yer idle up a bit since that's easiest then if that dosn't work then go for the electronics attack. GL man!
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914bob · Joined: 02 Feb 2008 Posts: 7 Location: Glasgow Scotland

Just the silver box - LH inner wing as ozzie - for me too.

What you reckon on best test of the AAV? I heard stick it in the freezer and it should open?
I suppose its most likely stuck open to cause my prob? need to check it out.

Cheers folks.

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

I don't think the AAV is the problem.

The best way to test it would be to disconnect the inlet hose, cover the AAV end with a piece of plastic wrap, and slide the hose back on.

Then start the engine when cold and observe for changes in operating characteristics. Idle should be lower when cold, and the mixture will be too rich. When warmed up, idle should be normal 800-900 rpm. Then when restarting hot, if the AAV was causing the 400rpm idle, since the AAV is blocked, the idle should be normal.

I suspect that if the engine has good spark plugs, ignition wires, ignition timing, camshaft timing, and valve adjustment, that the problem is incorrect mixture and/or idle speed setting, OR a bad WUR or sticking distributor advance.

Ozzie · Posted: Mon Feb 23, 2009 10:01 pm Post subject:

Definitely a process of elimination.
I had a bad vacuum advance- diaphragm was split. Gave me headaches trying to sort.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance