1973 2.0, original engine, completely rebuilt to stock specs about 10K back. Original D Jetronic still in place... new Cylinder Head Temp Sensor installed about 500 miles back. Cold Start valve disconnected... everything else original to the car.

Professional Porsche Mechanic has completely gone thru a major service and full tuneup less than 500 miles back. Fuel system was completely checked from the tank thru the injectors and is fine...

Car starts perfectly from cold, and runs fine for the first 10 to 15 minutes of driving, (which is about what it takes to come up to full operating temps)...

Then it will start intermittently cutting out and missing and often will not rev over 3,000 rpm...

If brought to idle, it will either drop very low, or completely stall. If it stalls, it is very hard to restart, and will only do so with the accelerator fully depressed...

BUT, it does not exhibit this behavior all of the time... occasionally, it will run fine for as much as 150 miles!!!???!!!???

So, in a nutshell, it apears to be an electrical issue that is affected by the heat/vibration of the engine during operation... All ideas to help pinpoint the trouble spot will be greatly appreciated!

Just a thought off the top of my head. Have you checked to see if you have a tight valve. If to tight when it gets hot it will loose compression.

I was having problems with my 2.0 this summer and it ended up being rust in the fuel tank plugging things up, but someone suggested (from personal experience) that it might be the coil-distributor wire that was going from conductive to insulator when it got hot. But these problems seem to have a ton of possible causes, so just check everything.

Points.

Ferg

I know you have replaced the cylinder head temp sensor but it sure sounds like your problem is related to the warm-up cycle.

One quick way to make sure it's not the head sensor doing funny things once it warms-up would be to temporarily bypass it. Unplug the sensor from the wiring harness by #3 cylinder. Take a wire from the neg. side of the battery and run it directly to the plug in on the harness, which will simulate a 'full warmup condition" to your ECU. The engine should be harder to keep running when it is cold until warmed-up. If car runs fine after that..you found the issue, a malfunctioning head sensor or a short in the wire that goes from the head temp sensor back to the harness. Tip comes from Dr. Atlanta's book.

Just one idea that is easy to check...

That is a Great Tip on how to check the CHT Sensor!

Thanks... it is always a good place to start looking!

Valves were just adjusted, but I guess it wouldn't hurt to recheck...

Anyone have issues with the ECU Plug In Connection having solder breaks not visible to the naked eye??? I understand that those can be an issue as well...

More ideas are still welcome... I will try replacing the Coil Wire also! It is likely 34 years old now!

When I got my 76 2.0, it was running rough and would hardly idle. Leaked also. So when I pulled the engine I went through the ignition harness, 12 pin from relay plate and found several wires that would not conduct at all. Also went through the fuel inj. harness and found several more bad connections. After replacing all defective wires and connections, the car starts, idles, and runs great.
When there is a bad connection, it will sometimes pass enough current to operate whatever it feeds, later after heating up and expanding, it will no longer pass enought current or voltage.
Years of working with things electrical and electronic has reinforced this concept time and time again.
Check all of your grounds and all of the harnesses. Bet you find a problem in there.
Tom

From the symptoms, I would be inclined to check the coil, and possibly the condenser (which, BTW, RARELY fail) As always, use the appropriate BOSCH parts. Might also check the integrity of the ground wire inside the distributor on the points plate. The Cap'n

That's plenty of time to hightail it over to Brad's!!!

Paul

He, He! Well, maybe if the car was still in IN, but it is in CT, and I am trying to help diagnose via long distance!

I am guessing that "Tom" nailed it, but just trying to decide where to start looking...

I had the exact problem with my '72 1.7. Turned out to be grease on the dizzy advance weights would melt when hot and cause the weights to stick. It drove me crazy for days because I 'knew' it was a fuel injection issue. Pulled the dizzy, cleaned up everything, installed, timed and vroom vroom.

Good luck!

edit:
I had the exact problem with my '72 1.7. It drove me crazy for days because I 'knew' it was a fuel injection issue. Turned out to be sticking advance plates in the dizzy. Pulled the dizzy, cleaned up everything, installed, timed and vroom vroom.

I am not sure exactly why they were sticking. I had to scrape off some nasty grease off the advance plates. Since that's all I really did, I am assuming the grease had something to do with it.



Good luck!

Sticking advance weights in the dizzy... that is one I didn't see coming, but it is VERY possible, because the dizzy was not rebuilt when the engine was done. It was fairly new (then), and was just put back in and hasn't been touched in over ten years!!!

FWIW, put in the new Coil and Coil wire, and that seemed to make a bit of difference. The car will show an indicated 120 mph and does it very smoothly, so the problem is not on the top end!!!

Am also going to test and swap in a spare 037 MPS, and see if that makes any difference... could it be slowly failing???

But cleaining up the Dizzy... I like that idea! THANKS!

Aren't the 037 MPS for a 1.7...2.0 should have and 043. Not to sure how and 037 would run.

Might wanna tell us how melted grease is stickier than semi-solidified grease. I could use a can of that stuff! The Cap'n

Actually, the 037 MPS was used on the 1.7's AND ONLY the 1973 2.0's...

And the original 037 has worked fine for 34 years (up until now, if in fact that is the issue???)

Of course, you have to match the MPS to the ECU and also have the correct CHT Sensor for it all to play nice nice together, but so far, I have been able to keep "all of the balls in the air"... Til now... :>((

*noob warning*
pardon the ignorance
what's a dizzy?

Distributor

Dizzy=Distributor


Oops, Rand beat me to it.

Well, the MPS checked out well within the 10% margin when the coil checks were done, so I suspect it is something else in the "System".

Have not done the CHT Sensor check yet, other than to make sure it is solidly seated in the Cylinder Head...

Next big step is to pull the Dizzy and have it properly cleaned and set up.

Stay tuned for more news at Eleven!

Lyle,

OK.

You live in Michiana, winter in FLA, and drive your car in CT?

You must have a plane!

Paul

He, He! Keeps me out of the bars and strip joints!!!

So to confirm, the 1973 2.0 MPS is the same as the 1973 1.7 MPS?