Seasons greetings and a happy 928 2022 to all - and back to getting my 928s4 running smoothly after head gasket and timing belt replacement.
With my engine back together, and new spark plug leads fitted (None to self- don't break the connector again!) I started her up and let the engine run till warm. The engine still sounded a bit rough but seemed to get better as it warms up.

The car starts very easy, with no throttle.

I decided to take it for a drive, and experienced the following:
Putting the car in reverse caused the revs to drop dramatically to just above stalling, and the whole car to shake. Same with putting it in drive. It is an automatic.

Applying some throttle smoothed every thing dramatically, but not 100% .

At partial throttle the car ran smoothly but does not like full throttle, where it has a distinctive stumble. Also, the gearbox shifts up to 4th very quickly at low revs, and is reluctant to shift down.

I suspected either an intake vacuum leak , or a ISV valve issue - so I removed my intake spider again to check.

While it is removed, I want to check the wires running to the ISV in case it got damaged during the engine work.

My question is, where do I find " the other end" of the wires on the LH and / or EZK connectors?

From the 928 Periodic Inspection 1987-1995 Models document, it seems to me to be pins 21 and 33 on the LH Connector, but would like to confirm.

I'll also test the ISV separately while I have access.

Thanks

 

This does not sound like an ISV problem to me. If the ISV is not working cold starts are difficult and need part throttle to pick up, when warm no problem as long as the ac is not running- stick the ac on and rpms will dive and the motor may die if no throtlle applied.

The ISV signal comes from terminal 33 on the LH.

 

So my ISV valve was stuck. I cleaned it out and lubricated it and now it works smoothly.
Will see if it solved the problem when the intake is back on.

 

It is quite common for the shuttle to get sticky and need cleaning- happened to my motor some 18 years ago leading to my first inlet manifold job. I found the shuttle with a greyish powder- no idea what it was but cleaned it out and it continued to work until I changed it out a couple of years ago.

I cannot relate the symptoms you described to this type of problem but no matter- let's hope your problem clears.