Desperately looking for help on starting issue

[Germanator]

My 88 911 has some issues when starting the engine and so far I wasn't able to track the issue down.
When I start the engine, there is some hesitation and then motor idles really rough, like it is running on 4 cylinders (for ca. 10-20s) and suddenly the issue is gone and the car drives like a dream. When I shut the engine off again and restart, everything seems to work fine. Only when I let the car sit for longer the same issue is back.

So far, I've changed the oxygen sensor, the temperature sensor was changed ca. 2 years ago and the measurements are ok. I also changed the distributor cap and the rotor. Which initially solved the issue for 1 week and but then the issue came back.
I also have a fuel pump sitting at home which I wanted to change next, but I am not sure if this is issue.

Any advice or help would be greatly appreciated.... this starting issue drives me crazy....!


Thx
Jurgen

[Chuck.H]

Hi Jurgen -

It certainly sounds like an ignition problem, similar to one I've had when I parked outside overnite and got moisture in the cap. Since you say replacing the cap seemed to affect the problem, I'd look into the spark plug wires, and also check the rotor springs are not broken. The springs don't affect timing, but they do adjust the relative position of the rotor to keep it 'phased' a the correct wire.

You can check your wires when it's dark - look for any arcing. Or, if you're a pretend tough-guy like me you can run your hands all over the wires while it's idling - any current leaks will be quite evident!

Chuck.H
'89 TurboLookTarga, 371k miles

[pdtweeks]

Based on my recent experiences in getting my new-to-me 3.6 transplant up and running, I would suspect the Idle Control Valve (Stabilizer).....it just might be sticking enough to cause initial starting issue that you're having. Removal and cleaning is a pretty simple task....this may be worth looking at unless someone more knowledgable disagrees.

[rusnak]

You might try testing the fuel pressure and CO% or AFR in open loop.

[ischmitz]

All good advice above. However, the bottom line: either find a good friend with another 3.2 or have some really deep pockets if you want to hip-shoot the issue by swapping parts. The parts route will get expensive quickly. I'd rather buy some diagnostics tools to get data that rusnak mentions.

And if you talk parts I would always start with the DME relay. Cheap and you should have a second one anyway. So this is not a waste of money.

Rough running can be spark or mixture or both. Remotely, it's impossible to tell which.

Good luck,
Ingo

[pors1968]

It might be fuel pump loosing pressure leaking check valve.

[Germanator]

thanks for all the suggestions!
I will try to go step by step to see if one of those will fix the issue.

[rusnak]

You might get lucky trying to induce a rich mixture with starting fluid, or a lean mixture by removing the oil cap. If the hard starting continues, then you know it's not due to mixture settings or a vacuum leak. It would be then time to check things like the CHT sensor, spark, etc.