924Board.org

Robb Northrup · Joined: 11 Oct 2006 Posts: 49 Location: Mesquite, Nevada

Folks:

I recently went for an emissions check (just moved from rural Illinois to Las Vegas) and the system wouldn't run the inspection because the car would not idle at less than 1500 rpm!

When I had some work done a couple of years ago (replaced the Air FLow Meter [Air Sensor Unit] and cleaned out the fuel tank) the mechanic adjusted the idle to about 800 rpm. However...

When cold, the car idles at 800 or so. But when warm (in 3-4 minutes) the idle moves up to 1300, then 1500 rpms. And it never goes down.

What gives! Nothing is covered in the Haynes manual.

Would appreciate any help before I'm forced to find a CIS specialist (read that as very expensive) here in Vegas.

Robb
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I've owned too many cars. 1980 Porsche 924 with European bumpers

Ozzie · Posted: Tue Oct 02, 2012 9:59 pm Post subject:

Sounds like it was adjusted to help starting when cold (which was really the problem)
Screw in the screw on the front of the throttle body will slow it down but may not start or run when cold.
Cold start problem is probably the AAV or WUR.
If the AAV is stuck open this will give you the symptoms you describe.
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Robb Northrup · Joined: 11 Oct 2006 Posts: 49 Location: Mesquite, Nevada

Hey, thanks for the info. But I'm puzzled by the abbreviations AAV or WUR. I don't recall seeing those in my Haynes manual.

Of course, our version was published for the US, which usually changes everything!

Robb
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I've owned too many cars. 1980 Porsche 924 with European bumpers

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

NOOBS READ.

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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Ozzie · Posted: Wed Oct 03, 2012 10:08 pm Post subject:

Aux air valve and warm up regulator.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

curtisr · Posted: Thu Oct 04, 2012 10:44 am Post subject:

Surely the linkage must need adjusting, no?

In the '87 you can follow the throttle cable til you come to an adjusting barrel that has two nuts to set the idle limit...
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World's worst welder.

!tom · Posted: Fri Oct 05, 2012 2:22 am Post subject:

The throttle cable adjustment is to take up slack in the cable, not to set the idle speed.
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78 924 NA
5-lug

Robb Northrup · Joined: 11 Oct 2006 Posts: 49 Location: Mesquite, Nevada

Folks:

Spent part of the day playing with the Auxiliary Air Regulator (also known as AAV).

I removed the unit from the car and plugged the line with a wooden dowel. Then started the car and watched the idle move from about 800 rpm up to 1200 after about 1 1/2 minutes.

I then simulated the Nevada emissions check by running the car at 2500 rpm for 12 minute, then backing off to let it run at idle. It idled at 1400 rpm as before.

So it can't be the AAR (AAV) unit.

Anyone have any other ideas? Would the Warm Up Regulator affect this?

Robb
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I've owned too many cars. 1980 Porsche 924 with European bumpers

joejax · Posted: Sun Oct 07, 2012 11:07 am Post subject:

Mine seems to do this on occasion, unfortunately I am on my third tach that burnt up again so I gave up on that for now, just have to go by feel.

When I blip the throttle, it tends to go back down to normal. I wondered if it was the idle stabilizer, I've jumped it out, but now I'm wondering if that is creating more problems, so that has been inconclusive.

It may be time to run some more fuel cleaner through, and bite the bullet and start using premium gas again, seems to run better on premium.

Something in the fuel dist gummed up, or the butterfly in the throttle body.
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I got nothin'
Uhhh...you got any pics?

fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

Probably leaking bushings in the throttle body.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

Muz924 · Posted: Mon Oct 08, 2012 4:10 pm Post subject:

I had a fast idle problem and narrowed it down to metered air by-passing the throttle via the brake booster vacuum line.

On my ROW (Australian spec) car this vacuum line has a "Y" piece that links back into intake duct just after the meter plate.

I blocked this pipe at point 'A' (refer my old thread) so that all engine vacuum was being applied to the brake booster.

Try clamping off your vacuum line to brake booster and see if you regain control of idle speed.

This was my thead.
http://www.924board.org/viewtopic.php?t=35465&highlight=

Hope it helps you!!
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1978 924 RoW 5-Speed (Current Project)
1980 924 RoW 5-Speed (Donor Car)
1985 Alfa Romeo Alfetta GTV 2.0 (Previous Project Car)

Ozzie · Posted: Mon Oct 08, 2012 7:42 pm Post subject:

Adjustment is via the screw on the TB
If the screw on the throttle body is in all the way then the "O" ring seal is shot.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Robb Northrup · Joined: 11 Oct 2006 Posts: 49 Location: Mesquite, Nevada

Thanks, Muz924. I did what you said: I couldn't clamp the hose near the intake air ducting, so I took a pair of pliers and -- while the car was running (at 1500 rpm) -- clamped the brake booster vacuum hose from the manifold; it dropped the rpms by 800!

So purchased a "splice" to connect the brake vacuum hose sections together, and blocked the port on the rubber air ducting with some wood dowel and a hose clamp (I have no idea what that vacuum prot is for!) and the car runs perectly and currently idles between 650-700 rpm. I may want to turn that up a bit, but I'll do that AFTER the emissions inspection (smog check here in Nevada).

At this point I have no way to check the effect on emissions (CO, NOX, etc.). I'll report that later this week.

Thanks again, all. 924.org is awesome!

Robb Northrup
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I've owned too many cars. 1980 Porsche 924 with European bumpers

Muz924 · Posted: Sun Oct 21, 2012 5:30 pm Post subject:

Robb,

I am glad my suggestion worked for you, always good to see a thread with a happy ending!

Cheers,
Santo
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1978 924 RoW 5-Speed (Current Project)
1980 924 RoW 5-Speed (Donor Car)
1985 Alfa Romeo Alfetta GTV 2.0 (Previous Project Car)