Porsche Enthusiasts Club Forum

Helping a friend with a newly bought 924s with undiagnosed engine problems - price reflected PO not being really very helpful with information. Signs are that the engine loom wiring has been disturbed and rewrapped, also AFM has at some time been replaced - it is not the original, but is the correct one....

Anyway the engine fires up willingly and smoothly enough but when it gets up to temperature and tries to knock off the cold start then revs drop but then immediately rise to previous level. It then gets into a cycle of knocking off the cold start, revs fall then rise back again every four or so seconds. Obviously the temp sensor is saying we are hot enough and sends its signal, the ecu starts to act on it but then goes back into cold start phase.

Where do we start?!

I would try replacing the ECU temperature sensor, it sounds like you've pretty much diagnosed it.

I had a similar issue to this recently, but it went away by itself, i've ordered one to fit this weekend anyway however
there is a testing procedure on Clarks, if you have access to some testing equipment i'd start with that

Cheers

hopefully it is just that simple - sensor on order

No the temp sensor wasn't the cause of the problem! Sensor replaced and the engine still pulses - tries to come out of cold start mode, but returns immediately to it every three or four seconds.

Anyone have any further ideas?

Cheers

Had similar symptoms recently were the engine would start and tick over bt was lumpy and cycling like a missed beat. Turned out i had accidently dislodged a vacuum line union whikst working on something else. Mght be worth checking the vac lines are all ok.

I don't like the state of the engine loom - it looks like a short has caused a small fire at some time, some of the sheath and connectors look a bit fried! I'll replace it with a good one and take a look at the vacuum hoses at the same time

Fingers crossed