Problematic stumble/misfire

[chally72]

I am never using the word "fixed" in association with Porsches again. Instead, I will use the phrase, "problem that went away for an indeterminate amount of time"

I'm having severe stumbling/misfire issues. I thought it was water in old gas at first, but after a fillup of 100 octane and dry gas, then another fillup of 100 octane, the problem came back. I cut the plug off of the harness side of the front speed/reference sensor and rewired it, because the first inch of wire was cracked, brittle, and green. She fired right up, and I headed to the gas station, confident that I had now "fixed" the problem for a second time. I filled her up, and not 30 seconds after leaving the gas station she started stumbling hard. So hard that getting her over 3000 rpm is an impossibility.

The issue is not related to injectors or fuel pressure. The rail has 45 PSI, and I get quite the backfire after she cuts out for a moment at RPM, meaning somehow I lost spark.

Switching DME's did not cure this issue.

Anyone have any other ideas? I'd appreciate any info on how I can further diagnose this.

Thanks!

[Grandad#3]

The Throttle Position Switch (TPS) is giving you problems. Check out the link below and see if it describes your problem to a "T".

Throttle Position Switch - Information, Troubleshooting, Replacement, and Adjustment

Cheers,
Larry

[chally72]

Spot on. I unplugged the TPS, and no more misfires/stumbles. Just a 2000 RPM idle and a rich tune. Thanks! I redid throttlebody seals when I rebuilt the engine, but too little, too late for my poor TPS, I guess.

I'm going to crack it open today and see if I can't fix it.