Doms964TurboII

Car start cold perfectly, will run for hours on a motorway with no problems. However occasionally, when ticking over in traffic the tickover will drop below normal and then a second later it will die. Wont start (try resetting alarm etc- noting)
Once the car has sat for a few mins it will start and run fine for an indeterminate length of time???
Engine still pretty hot when it restarts. (2-8mins later)
Been scratching or heads
Grateful for any ideas
Many thanks

Been thru below!
Turbo control module(how expensive!!)
Earthed overboost

heliolps2

I would start with the basics,
Like pull the intercooler off and make all the hoses too and from the turbo are connected correctly and tight, and the vacuum hoses are nice and tight,
I had my intercooler hose slip off the turbo slightly and I could't see it and the car would die, then start and once I hit boost it would slip off and die when I hit traffic or came to a stop, thats one place to look, It could also be the Turbo control unit , You can find those used an ebay.

Good luck
Helio

Metal Guru

Once I didn't have the compressor hose clamp tight enough at the intercooler gooseneck and the engine was really rough on boost, but it idled fine.
I would look at idle mixture. It might be too rich or too lean. I would set it at stoich (14.7/1).

speednme

Bad fuel pump (one of the two) or bad fuel pump relay

mitchy965

vacuum leak!! have a shop with a smoke machine (visible vapor) test it.

Metal Guru

Smoke may or may not detect a leak.
I had a cracked injector block on #1 cylinder. The crack was facing backward, right where the tech could see it.
It was not detected.
In any event, a small vacuum leak only causes idle problems, not the severe issues the OP is experiencing.

Doms964TurboII

mel_t_vin

Was the overboost protection relay [911.615.118.01] from the 930, aka Yellow Relay, carried over to the 965?

Metal Guru

Mel, the overboost signal goes to the Turbo Control unit, which functions as a safety relay.
What I've seen with my car (I have a LM-1 semi-permanently hooked up to my exhaust) is that when the engine is heat soaked, the WUR leans out the idle mixture but after fresh fuel cools the WUR, idle mixture returns to normal.
It's a flaw in the system design.
I saw 20/1 afr at idle last Friday as I left the Porsche corral at the Detroit Grand Prix. Ambient temperature was low 90's and my car had been sitting in the sun for 4 hours. My idle speed was good but I could see where a CIS unit/intake needing attention might have low idle speed and stall.
Our cars are old now and the perishable parts may need replacing.