rsathre

i Have a 1990 C4 cab. Intermittently, I turn the ignition key, and the motor starts to turn and then just stops. Explaining this statement more fully…it sounds like a rotating part comes to an abrupt halt. If I immediately crank it again, it will do the same thing. If I wait a few seconds, turn the key to the accessory on position, wait 3 seconds, there's an 80% chance it will crank up.

Any thoughts..

I have changed the battery bc it failed on me and was 8 years old.

Thats the only thing I have done. Don't even know where to start on the troubleshooting.

Thx
Raghu

Silvertarga

Had similar problem,
Check ground at battery and at starter
Check yellow lead from ignition switch to starter (that was bad on my car)
I replaced starter, ground cables, etc and finally narrowed it down to the yellow wire off the ignition switch being broken somewhere along its run

Babalouie

I'd also clean out the ISV: https://rennlist.com/forums/8961949-post76.html

And if that fails to fix it, take the car to a Porsche mechanic and ask for an "idle adaptation". It's like a forced-reboot of the ecu to reset the idle settings.

Wait a sec...do you mean that the starter stops cranking?

sml

sounds more serious than an ISV clean or system adaptation with bosch hammer.

FeralComprehension

Attache a volt meter to the battery terminals and observe Vbatt while cranking. I also like the starter ground theory.

Either way, sounds like not enuf juice.

DaveK

Mine did that for years (if it didn't fire immediately, it would turn over for about 2 seconds and then stop suddenly and make a noise a bit like you'd stuck a big stick between the spokes of a spinning wheel). Then one day, the starter motor failed completely and was replaced.

Never did it after that.

rsathre

Before I change the starter motor .....

I looked at several other posts. One member suggested pushing the accelerator to the floor for 15 seconds before starting the car. I did this, and it seemed to fix the problem. So I assumed it must be the idle control valve. I undid the valve and cleaned it out. There really was no gunk in the valve. So, if i do the accelerator thing on a cold start, it cranks pretty much every time. If I do it on a warm start...it does the same think. I recorded what it does...

Any thoughts...
Should I change the starter?

cobias1

have you checked the fuel pressure ?

Navaros911

With a bad starter the car will not eveen start cranking. You turn the key and all you hear is aa single click. Multiple rapid clicks could indicate and electrical supplu issue (batt or circuit).

If it is the starter, tapping it gently with a wooden mallet may get it to work again. Sometimes after trying once (and hearing the single click) it will start... But it could stop all together at any time.

Just to make sure we have all the info here: you keep the key turned to the start position and while you are doing that the engine stops turning?