Porsche Enthusiasts Club Forum

Just thought I would round up this thread as I have finished my diagnosis and can confirm my ICV looks like it is ok.

I thought the system was configured such that the ICV has a variable live connection and a straight through standard earth, but it appears that this is not the case. The ECU actually looks like it controls the ICV position via the negative wire connected to pin #1, with a steady, permanent 12v live running through the positive wire connected to pin #2, so the ICV is actually controlled through what I thought originally was the earth wire.

I tested this by creating my own test earth back to the inlet manifold and then starting the engine. This resulted in the ICV being permanently closed which made the engine keep revving up to 2000 rpm at Idle and then the ECU pulling it back down to 1000 RPM.

Returned the wiring back to normal and the ICV started to restabilise the RPM. Disconnected the engine runs a bit rougher as expected, minus about 100 rpm.

Looks like the minor fluctuation when idling is down to something else. Ruled out the TPS and ICV, so going to check the AFM next and also do a proper vaccum check to make sure there are no minor air leaks or anything.

At least I have a clean ICV now anyway!

Dave.

The main earth strap is on the bulkhead and connects to an 8mm stud that sits at a 45 degree angle on the bell housing. The main engine loom earth lead is also there. Well worth the fiddly job of pulling them off and cleaning. You will probably find your engine spins over faster with it cleaned. May also help your poor idle as well. Usually find a good bit of corrosion on them. 2 minutes with emery cloth makes all the dofference. Remember to do the bulkhead connection as well.
Alasdair

The main earth strap is on the bulkhead and connects to an 8mm stud that sits at a 45 degree angle on the bell housing. The main engine loom earth lead is also there. Well worth the fiddly job of pulling them off and cleaning. You will probably find your engine spins over faster with it cleaned. May also help your poor idle as well. Usually find a good bit of corrosion on them. 2 minutes with emery cloth makes all the dofference. Remember to do the bulkhead connection as well.
Alasdair

What are your symptoms to make you think you have a problem with the ICV?

Golf's sometimes have an ICV which buzzes with the engine on, but not the 944 S2, although some porsche models do. Its just down to different engine management strategies.

If your car is stalling at junctions, idling poorly or something else, I would suspect you have another problem, which may be as simple as a vacuum leak or an airflow meter with a worn track.

I have not had to change a 944 ICV in twenty four years of working on them. I have had to clean a couple, and I really do mean a couple, but not change them... In fact, I think every one I have cleaned has been to rule out a cause and not actually been the cause once it was ruled out.

Hi Jon,

Thanks for the reply. Symptoms are a very slight fluctuation in rpm at idle (I mean very small). Then when driving and I take my foot off the throttle the engine seems to judder as if the rpm is dropping too low and then the ECU is correcting it again. Accelerating gets rid of the issue, most noticable in lower gears.

Also if I accelerate when the car is stationary the rpm goes up but then drops when I take my foot off and then again, feels like the ECU catches it (in the same way as described when driving). It is not so bad that the car stalls at junctions or anything like that and I can still drive the car ok, but it is noticable (to me anyway) and I would like to get it fixed really.

Also if I just blip the throttle very quickly (and i mean really quickly), it sort of does a small rev and then another rev (kind of delays it), again this seems to be the ECU doing some form of correction to the idle. If I just accelerate normally, rpm goes up as you would expect and then drops lower than idle and then the ECU catches it and then it stablises with the tiny fluctuations in idle as described above. New acclerator cable helped the trottle response loads as the last one was limp, stretched and I couldn't tighten it anymore.

First thought was the TPS, but I have tested it at the plug and I am getting the expected voltages when I have the throttle open and closed as per a testing guide I found on clarkes garage (I think that is where I found the guide). Also disconnecting the TPS effects the idle, so it is definitely doing something. I know faults with the TPS only sometimes show up when the engine is hot, but this problem is happening even when I first start the car, so doesn't appear to be heat related.

I can't seem to find any noticable air leaks (i.e. none of the pipes look split and everything is attached securely), but is there anyway I can test that for sure?

Next thing I was going to diagnose was the AFM. Again, disconnecting it effects the RPM so it is definitely doing something (as were the ICV and TPS). It is just appears to be one of those pain in the backside niggling issues that doesn't have a straight forward "yes this is broken and needs replacing/fixing" solution. I want to diagnose it properly instead of the just throwing in new parts until it works approach, as I don't see the point in replacing parts that don't need changing.



Cheers Alasdair, will check that tonight.

Dave.