PR89928GT

89 928GT 5SP

I have had on and off again problems with the idle staying high and
then coming back down after 10/15 min. Now it seems to stay at
2700-3200 rpm at idle and does not come down. Can I reset the idle
stabilizer or up stuck it , or does it need to be replaced. I have heard
that it can be rebuilt what is the best way to do this also taking the $$
into consideration.

SeanR

Best way is to go in and do the entire intake refresh. There are a number of items that can cause the high idle and a faulty ISV can do this. They are a sealed unit that can not be rebuilt but you might be able to use some lubricant and a 12v power source to get it working again. It is sandwiched between the upper and lower intake so getting at it requires removal.

Best to replace all the hoses, knock sensors and gaskets when you do it. And it's a great time to paint it up the way you want to.

Lizard928

Pull the carpet back off the gas pedal first!

Speedtoys

Go Here:

http://dwaynesgarage.norcal928.org/1...ke Refresh.htm


Where are you? Can you add that to your profile..you may need help..and help is out there.

John Speake

Hi idle speed is due to an air leak into the intake, often the hoses to the ISV are split. Intake refresh required !

ROG100

The problem with the ISV hose splitting can be overcome by adding clamps as per PET.
Hose 928 110 174 09 was not originally fitted with clamps but current PET shows the addition of clamps.
The hose is a molded hose and two halves are joined together. It seems to split at the join. The addition of the clamps will stop it splitting.
I have made Porsche aware of this through PTechs but so far no change in the hose. With enough warranty returns they may take notice.
The hose clamps are 999 512 374 02 x 2.

PET now shows clamps on all the hoses under the manifold.

shawscove928s

When my 86.5 sits for a couple of weeks with the battery disconected the idle is erratic untill it warms up. After the it warms up the idle settles down and the car idles and runs normally from then on. Starting cold and driving all remain normal untill I disconnect the battery again for storage. I think disconecting the battery for a period of time may cause the ecu/brain or whatever drop it's program. A 15 minute warm up and then a half hour of normal or spirited drive seems to reset it.

I know, I know, "drive it more store it less" will solve allot of these kind of problems.

John Speake

85/86 LH ECUs don't have any stored adaptation parameters like the 87 and later cars. There may be a problem with damp in your ignition leads when left for a period ?

FredR

If your idle speed is 3k then it is time to remove the inlet manifold. Fully agree with Roger about checking the hoses and using clamps- have done so for nearly 10 years. I did once have a problem with an erratic tickover- found what looked like a dry dark powder in the ISV. Blew it out with pressurised air until it was clean and squirted a little bit [a short squirt] of WD 40 in there until the shuttle moved back and forth easily.

That was years ago and the unit is still working fine today.