Carpokes Porsche Forum

I just experienced this situation over the weekend. This may be old info to some but was new to me so just in case I didn't search correctly here and it has been posted....

I warmed the car in the morning to change my oil Saturday, let it sit for 2 hours to cool to the touch, and popped the lights up and moved the coil wire from the distributor to give better access to the filter. Drained, filled, replaced everything and started to check for leaks and oil level, but the car would start then die immediately. Tried several times and I could massage it to keep it running (poorly at best with an occasional cough) and get it to 3K but it would just drop to a poor idle then die when I released the throttle pedal. Tach would function and oil pressure was great. I thought maybe an old coil wire had seen its last days or the fuel pump was having issues, the car is 35 years old......
Google searched and found several possibilities from loose rotor from bad set screw to injector issues, bad plug wire, fuel pressure regulator, AFM, KLR and then a post on Reddit....

Per a post on Reddit, "It could be the throttle position sensor, something similar happened to me when mine died. Just unplug the sensor on the throttle body and try and start it. It should run fine but just have a little rev hang when unplugged. It just defaults to a richer fuel table when unplugged so it’s fine to run it like that"...so I unplugged the TPS and started and no issues...ran and idled fine. SO, I reconnected the TPS switch and drove around the neighborhood and issue was gone. I'm thinking it was coincidence with oil change time and just a bad/corroded connection at the TPS.

Hmmm... At first, it sounded like a big vacuum leak or bad AFM signal, both of which can produce start and die symptoms.
But based it clearing up after re-seating the TPS, it sounds like an electrical glitch indeed. All of the junior timer connectors can fray where the wires exist the plastic connector body. This thread shows that in detail:

viewtopic.php?t=565

Definitely possible the TPS connector just (coincidently) needed to be re-seated to break through a corrosion layer, but it if happens again I'd peel back the rubber boots and look for frayed wires. It's possible the harness got jostled while working on the car, and disturbed a frayed wire somewhere. (And, sadly, no guarantees its even in the TPS connector.)

Re the Reddit post, on the turbo, the DME/KLR detects 3 different TPS states: idle, part throttle, and full load (WOT). Without the TPS connected, if you floor it, the DME will not know to switch over to the WOT maps, which could result in detonation, blown head gaskets, etc. So I'd agree it's fine to run like that for short, light-throttle diagnostic drives, but not for much more.

I also read lots of suggestions of vacuum leaks and constantly fear the dreaded old wiring concern after reading many experiences of others. Thank you for highlighting your previous post and do remember reading that as a caution of future woes. I've read some posts of others that enjoy making new harnesses and am envious of their skill, knowledge, patience, and enthusiasm. I believe I just lucked out this time and accept even a blind squirrel finds an acorn once in a while. I just thought I'd pass this on as another item to consider should someone else have a similar occurrence to possibly check and will keep dreaming of a beautiful new Kroon harness while reminding myself everything matters. Ultimately overall success is in the details.......

ROB III wrote: Tue Aug 20, 2024 6:49 pm I also read lots of suggestions of vacuum leaks and constantly fear the dreaded old wiring concern after reading many experiences of others. Thank you for highlighting your previous post and do remember reading that as a caution of future woes. I've read some posts of others that enjoy making new harnesses and am envious of their skill, knowledge, patience, and enthusiasm. I believe I just lucked out this time and accept even a blind squirrel finds an acorn once in a while. I just thought I'd pass this on as another item to consider should someone else have a similar occurrence to possibly check and will keep dreaming of a beautiful new Kroon harness while reminding myself everything matters. Ultimately overall success is in the details.......

Fingers firmly crossed for you and your car!

You can try driving it again after some time, or have it repaired by a professional.

jonas22 wrote: Wed Aug 21, 2024 2:28 am You can try driving it again after some time, or have it repaired by a professional.

That is the plan.
Thanks