Glenncal1

Hey guys-my new to me 1985 US has a problem with idle while cold, car starts fine and just acts like the choke isn't working if it was a carbed car. You can hold the throttle to about 1000 and it will stay there and when the car is warm it idles fine. ISV? The PO replaced the Thermo 2 switch. Thanks Jim

SteveG

I haven't driven a car with a choke for 20 years so I'm not sure what you are describing. Does it hunt, betw what points? Does it load up? What happens when the temp needle starts to move? Did you check the output on the new Temp II? If the vacuum lines and hoses under the intake haven't been replaced, you probably have a vacuum leak and WYIT, replace the ISV. And with the intake off, powder coat. Welcome to the tank.

John Speake

When the engine temp is cold, the car runs open loop until the O2 sensor has warmed up.

In this time period, you are reliiant on the MAF signal being correct.

There may be an airleak causing the lean running, or the MAF may be badly aged which has the same effect.

How many miles on the car ?

IcemanG17

Does sound like the Temp II sensor....test its resistance vs temp with a multi tester....here is a good write up

http://www.electronikrepair.com/wst_page9.html

My 88 still idles low during warmup....around 4-500 rpms unless you touch the gas a little bit....temp sensor is fine..MAF is fine...no faults during spanner test....its weird....it does seem better when its warmer outside & if I drove the car the day before....it doesn't stall....just idles low until you give it a touch of throttle for a few seconds...then goes back to normal?

FeedNfrenZ

Sounds like a sticking idle stablizer. Kinda hard to get to but not as bad as the 1987 and up

Glenncal1

The car has 130k on the clock and just passed colorado emisions today with flying colors, when cold the idle is low and will drop sometimes and almost stall, again the closest comparison I cam come up with is a carbed car where the choke isn't closing when cold. Jim

whitefox

HA, what a pain the *** on my 87.

VehiGAZ

Glenncal1 - Jim,

Do you ever get this problem fixed? If so, how?

My '89 GT (30k) does the exact same thing after sitting for a few days, but not after only a day or less (no data in between). Specifically, if it's been sitting for a week, it starts fine but then stalls immediately, unless I give it a bit of gas and hold it for 30 seconds or so. If it sits for less than 2 days, it starts and stays running just fine. The PO set the idle to about 1200 rpm with the throttle cable adjustment - I think to compensate for this problem. I dropped it down to about 1000 rpm at idle.

A vacuum leak seems like a likely culprit, but you never know. Also, there is another thread suggesting to "rebuild the LH" for a similar-sounding problem - I'm guessing is the injection system itself though (the LH control computer can't be "rebuilt," can it?).

Any other guesses anyone?

I'm going to bring it to a local Porsche shop for a complete physical (and to fix this problem) once I get some minor things fixed up, but I like to have a good idea of what the problem instead of telling the mechanic, "I dunno what's wrong - just fix it and bill me proportionately to my ignorance."

Thanks for any help!

John Speake

Yes, part of the LH ECU can be rebuilt (actually replaced with something much less failure prone).

In your case I don't think the problem isan LH issue.

How many miles on your car ? If over 80k or so, the MAF is a possibble suspect for the problem.

Also check for vac leaks.

VehiGAZ

30k miles on it, but the MAF is 18 yrs old now, so...

The PO replaced a bunch of hoses when he bought the car about 4 years ago, but I didn't see any mention in his documentation of vacuum hoses, so maybe that's it.

Is there a procedure posted here somewhere for checking vacuum leaks?

Thanks!

John Speake

MAF shouldn't be the problem at that mileage.

Search the archive on vac leak techniques....

VehiGAZ

Thanks John! I will start hunting for vacuum leaks.