1989porsche928

I have been told my the transmission mechanic, a Porsche mechanic told me my transmission was bad and a few people my IDLE sounds bad. I really don't know what everyone is talking. I might just be like one of those cat owners, their house smells like cat pee and they don't even know because their so use to it. Anyways before purchasing and experimenting with an idling tool what is a good idle? Does the idle change when the vehicle starts in cold weather? Is their some reference on how to calibrate the vehicle? When I start my car in the cold the RPMS are very high. It lowers as the vehicle runs for 30 minutes. If you were asked to make an idle correct in an 89 928 what would you do? thanks

jcorenman

I wouldn't know about cat pee, but the idle on the 87+ cars is regulated by the ECU brains, controlling the ISV (idle stabilizer valve). For an auto the idle should be 675 RPM once warmed up, and a little higher when cold. If it is higher than that then there is an air leak somewhere, or a bad ISV.

You will need to pull the intake and either do a complete refresh (plenty of threads here), or do a careful inspection for rotten/split hoses and replace those-- with the understanding that you will be back in there for the others, at some point.

Cheers, Jim

Avar928

Didn't you just have your transmission rebuilt? How can it be bad after that? What did they define as "bad"'? Need more details. What rpm does it settle at for idle?

I don't think you need an "idle tool" for our cars so as long as you have access to the workshop manuals and a full tool box.

Basically everything Jim said can and do affect idle. I'm having an idle problem at cold start as well I'm currently hunting down. It could be a lot of things or just one, never know until you get in there and check and rule out one by one.

1989porsche928

The idle was bad before the rebuild. The rpm is over 1000 on startup and even higher when cold.

Avar928

What's been done/repaired to the car since you got it?

TheoJ

like Jim said: sounds like unmetered air getting in. A good test is warm up the engine, stop, disconnect battery, wait 1 minute, reconnect battery, start the engine. Idle should be 675 or so in a minute. f it does that and gradually climbs back up to 1000 rpm you have an intake leak. Maybe a small one. Check dipstick and filler cap for proper sealing too.
regards
Theo Jenniskens, 1992 928GTS, the Netherlands

dr bob

In Dwayne's intake refresh picto-tutorial, he shares a simple-to-build fixture for chacking the intake system for leaks using a little air pressure. The drive to the Home Depot will cost about thesame as the parts needed to build his tester, assuming you have compressed air and a pressure regulator. Just a couple PSI is enough to find most leaks. Solve that side before you go after the electronics and the ISV for faults. My too sense anyway.

1989porsche928

thanks dr bob. I recently saw a video on YouTube with someone who has a a vacuum leak. He was able to remove the front oil neck and water housing (can't remember the name). I was impressed because he did not remove the intake.

Avar928

Key point, make sure you have the two o-rings for the MAF. I only had one. If I revved the engine you could hear a "sipping" sound which was air being sucked into the gap. Messed up my idle as well. Kinda sounded like a turbo...didn't really do too much for the car though.

worf928

Auto transaxle has a vacuum line from the engine to the shift modulator.

If the idle characteristics are different after the transaxle R&R then my bet would be that that vacuum line is not connected. If so, the transaxle will shift really hard at anything less that almost-full-throttle.

1989porsche928

Worf I think the idle was bad before and after the trans rebuild.

worf928

After-market chips in the ECUs can also screw-up idle.

But, looking for intake leaks should be then first step as above.

Hilton

Just to make sure its clear from Jim's post, before you spend money you don't need to.

There is no "idle tool" which will help. The idle speed is determined by the chips in the ECU, and is determined by the factory (i.e. 675 rpm, or 775rpm for an 89-91 GT). The screw on your throttle body should not be touched - it was set by the factory to calibrate for manufacturing tolerances.

If your ECU isn't able to get the idle down far enough, you're looking for intake leaks.