924Board.org

[Morrie]

My 87 924S idle drops a couple hundred RPMs when the AC is on. I was told that early 944s had a compensation device attached to a bracket on the back of the air box, and that later 944s are controled within the ECU. Where does the 924S fit in.

Also, what, if anything, is indicated when the idle speed increases a couple hundred RPMs when jumpering the diagnostic plug for adjustment? Is this normal or is it a sign of another posible issue.

Morrie

[John_AZ]

Your AC idle is controlled by the Idle Control Valve (ICV) or some call it the Idle Stabelizer Valve (ISV). It is under the intake manifold in the rear.

You can clean the ICV. Check the hoses for cracks by the bends. Also check the wire connection is clean and secure. A signal from the ICV is sent to the DME computer to adjust the idle with or without AC.
You may also want to get ICV rubber mounts if yours have dry rotted.

Usually it is easier to remove the intake manifold and do a bunch of maintenance all at once.

GL
John_AZ
1988 924S + 1987 924S

[Morrie]

Thanks! I can see it under there. What would be a good punch list of things to take care of while the intake manifold is off? Sounds like a project I could complete within a weekend with a little preparation.

Morrie

[John_AZ]

Morrie,

Yes, you could do it in a weekend unless you send your injectors out to be serviced by www.witchhunter.com or local injector service. I did a DIY cleanout. I found the "O" rings and "hat" at a local VW parts house because the OEM Porsche kit was slightly different in hat size. About $5 an injector.

Get 4 intake gaskets-one is placed upside down-watch carefully.
PLUG THE TDC HOLE ON THE BELL HOUSING WITH TAPE!!!!!!!
Get a vacuum hose kit and the "T"s and elbows if needed
Get the ICV rubber mounts 2
Plan to check your reference sensor gap
Look at the heater control valve and small "J" hose on top. If the heater control valve has a white deposit-replace, its leaking
Get AOS seals--you must do this. It is only possible while the intake is off
Get new hose clamps for the OEM pinch clamps. I use fuel injector clamps or nonperforated screw type.
Check the bottom of the intake boot. It rots under there.
Clean the ICV-carefully.
Replace the DME temperature sender.
Check all hoses for leaks. Some cannot be replaced without taking off the intake.
Clean the negative cable ground and all others.
Check the negative cable for battery acid corrosion at the bell housing
Clean the intake inside with a stiff bottle brush
I know I missed something but this will get you started

GL
John_AZ

[edredas]

Check your throttle position switch (TPS)... it's what activates the IAC/ICV/ISV.

When the TPS is triggered, it tells ICV to bring the car to idle and will make adjustments from there...

To test the TPS, gently roll the throttle cam off the stop and listen for a click... if there is no click, TPS is out of adjustment. Even if you hear a click, you should check the TPS with a multimeter to assure it's working correctly.

The TPS is located on the bottom of the throttle housing and you can find a troubleshooting guide below.

http://www.clarks-garage.com/pdf-manual/fuel-06.pdf

While the symptoms may not sound like your problem... sometimes the TPS will stop working and someone will adjust the butterfly valve screw to bring the idle down... and this works fine until the A/C is turned on...
_________________
'84 944 -White, Brown interior
'84 944 -Red, Automatic
'86 944 -Garnet, Fully loaded, Koni suspension
'87 924S -Red, 300hp 951 swap
'87 924S -Red, Project Car
'88 924S -Red, Daily Driver

[Morrie]

My TPS is clicking and checks out with a meter. I can tell a definite difference when I disable it so I feel its probably doing its job.

My idle also is a little low when cold. Does the ICV also handle cold engine enrichment or do I need to examine O2 sensor feedback of some kind.

I am going to just plan to replace the ICV. I see rebuilt ones available and am wondering if they are "just fine" or if I should go for new. Generally new is better but there are cases where manufacturing quality is so varied that the rebuilt parts are actually better.

Morrie

[John_AZ]

Before you go out and spend money on the ICV, give cleaning a chance.
The ICV is not complicated and easy to test and clean. Here is one way to do it.

http://www.texasblake.com/porsche/tech/icv.html

GL
John_AZ

[Druman]

Could this also be related to the reason behind my RPM's going down when I turn on my lights?


7osh
_________________
87' 924S non-sunroof (Red) 45K miles
85' 944 "early" NA (Red) 130K miles

PORSCHE pisses excellence...

[edredas]

[Morrie]

[edredas]

[Druman]

My RPM's don't come back up until I turn off my lights. I have (what I think is) a very good battery, it's one of those yellow tops from Auto Zone. I just know it's pretty expensive, but I'm not sure how old it is. I got it with the car. I guess it could be the issue, I'm just looking for a cheaper fix I guess :\


7osh
_________________
87' 924S non-sunroof (Red) 45K miles
85' 944 "early" NA (Red) 130K miles

PORSCHE pisses excellence...

[edredas]

Well, you should always clean your terminals and have the battery tested before replacing... that shouldn't cost much.
_________________
'84 944 -White, Brown interior
'84 944 -Red, Automatic
'86 944 -Garnet, Fully loaded, Koni suspension
'87 924S -Red, 300hp 951 swap
'87 924S -Red, Project Car
'88 924S -Red, Daily Driver