924Board.org

keithiopian · Posted: Sat Apr 08, 2006 4:10 pm Post subject: start-up issues

quick background: this car sat in a garage for 10 years, had 33,000 miles on it. fixed it up, got it working again, flushed the fuel system, changed the belts, all that jazz. still wasn't running right, wouldn't pass smog. Took it in to a shop and had them clean out the injectors, ran like a champ and passed smog no problem.

now, to the issue: if the car has been sitting, it WILL start up, but it tends to idle a bit rough, and only at about 500 RPM. Here's the kicker - throttle response is weak until about 1300 RPM, when BOOM, engine hits its stride and jumps (without any extra throttle pressure) up to about 2400 RPM. Now as the car is driven, the idle gets smoother and smoother, and comes to rest eventually at a steady 900 or so as it should be. Shut the car off and come back a few minutes later, stays at a pretty strong idle. It's only after its sat undriven for a while that it starts out a bit weak.

any suggestions on this one? ideas i've had are a possible air leak (although this doesn't really explain it running well after being driven...) or a cold start valve/auxiliary air valve problem, but I am in Los Angeles and so even near-freezing conditions are pretty rare, and these suckers are from Germany.

I'd love any feedback you guys can give me on this one!

Keith

Ozzie · Posted: Sat Apr 08, 2006 6:22 pm Post subject:

Faulty control pressure regulator or WUR as its also called.
Do a check on the AAV first.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Paul · Posted: Sat Apr 08, 2006 11:08 pm Post subject:

This is a 78 correct?
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

keithiopian · Posted: Sun Apr 09, 2006 2:42 am Post subject:

it is indeed a 78. as for the CPR, I checked it while I was flushing out the fuel system, and got indeed a 20 ohm resistance across the terminals. however, this was a few months ago, so it could do for another check...what leads you to believe it is a problem with this/the AAV, as opposed to the cold start valve/thermo time switch? my only thinking on it was that if my engine was running like crap before the injectors were cleaned, and fine after, it would stand to reason that the cold start valve (which is essentially a fifth injector) could be similarly clogged up. Also, an improper spray from the valve could cause the sporatic up and down fluctuations in RPM I get while its idling rough at startup. thanks for the responses guys, future help is of course more than appreciated!

Paul · Posted: Sun Apr 09, 2006 2:50 am Post subject:

The cold start valve only works when the starter is being used and then only for about 10 seconds. The AAV is the next thing to check as it is responsible for providing extra air when the motor is cold. Yours may have failed in an open condition which makes the motor idle too high when warm. To correct this most people crank down the idle speed, then wonder why it idles at 500 rpms when cold.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

Chrenan · Joined: 15 Jan 2003 Posts: 3903 Location: Canada

I third the AAV suggestion. I had similar symptoms until I replaced a faulty (worn out) AAV.
_________________
1987 951 - M193 Version for Japan

Ozzie · Posted: Sun Apr 09, 2006 6:13 am Post subject:

If the WUR is mechanically jammed shut/faulty this would not show on an electrical check.
This affects your fuel pressure to the injectors.
The CSV has no effect on idle/running unless jammed open.
It is only used when starting.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

By all means check the AAV operation because it's easy to do, but I'm with Ozzie on this one: It sounds more like a stuck WUR to me.
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

keithiopian · Posted: Tue Apr 11, 2006 12:13 am Post subject:

thanks guys, as soon as i get a chance (and a day without rain) to get under the hood i'll check out the AAV. kindof hoping that's the problem, as i don't particularly want to go digging to get to the WUR...

do either of these offer an explanation for why it jumps about 1000 revs once it hits about 1400 without any throttle pressure?[/quote]

Smoothie · Posted: Tue Apr 11, 2006 1:03 am Post subject:

For the low cold idle, I'd be looking at the AAV first. If the WUR were jammed shut or clogged, you'd have higher pressure above the plunger in the fuel distributor, resulting in a leaner mix - which obviously would at least result in rough running, but I think the problem would be more severe as in no idling at all. In addition, normal running (after warm-up) would also be affected by a too-lean mixture if the WUR's shut.
Any possibility that you have an ignition distributor problem - sticking centrifugal advance mechanism or incorrect ignition timing?
Of course vacuum leaks shouldn't be dismissed. They'll pull tricks on you that you could never predict. -A split in a plastic vacuum T can for instance open and close with temperature and vacuum level changes and the same is possible with rubber parts.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

zwoodward · Joined: 07 Mar 2006 Posts: 58

I have a similar problem so after testing my AAV for the correct voltage and resistance I followed the procedures in this article
http://www.landsharkoz.com/images/pdf/wurfix.pdf
( I really think it should be in the FAQ somewhere) It didnt fix my problem so I'm pretty sure mine is the WUR but you won't believe how much gunk will come out of your AAV, you'll have to clean it several times with brake cleaner (something similar that doesnt leave a residue is probably good too). Then I adjusted mine according to that article, when it was cold, when it was hot, and when it was outside temp hoping to get the best adjustments possible. I did notice improved throttle response though not sure if that had anything to do with it.
Zac

Ozzie · Posted: Tue Apr 11, 2006 10:49 am Post subject:

This doesn't happen often but check your vacuum advance in the distributor.
Mine was faulty.
This would leave the centrifugal advance only working which needs revs to activate.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

keithiopian · Posted: Sun Apr 23, 2006 7:35 am Post subject:

so i finally got a chance to get under the hood, took out my AAV, and sure enough, when cold it was all the way closed...a little strange because mechanically it wasn't jammed, but still, probably the culprit.

i'm not confusing myself here, its supposed be open when cold and then slowly close, right?

Paul · Posted: Sun Apr 23, 2006 8:25 am Post subject:

Yep, open when cold, closed when warm.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

It depends how cold is cold.

When the engine's been running for a while (i.e. it's nice and warm), the AAV will be completely closed (i.e. no daylight coming through).

When the engine's been off for several hours (i.e. 'cold'), but the outside temperature is above, say, 5°C/40°F (does it ever get that cold in LA, Keith?), all you will see through the AAV is a tiny square hole about 1 mm across.

Only when the outside temperature approaches freezing (and below) will the AAV open up apprcieably,until about half the diameter of the pipe is exposed.

Where did your AAV sit on this scale, Keith and what was the outside temp?
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org