Wikkid911

It is with deep regret that I am actually posting to the board with a problem. After performing my search it has left me with more questions than answers.
My car has run fine for nearly 12 months since the top end rebuild which is its longest trouble free period I have had in 4 1/2 years but it has now developed an annoying hesitation at about 3-4000 revs. It doesn't do it all the time and when it does I can accelerate past it and it seems to be ok. The car ticks over great and starts first time but with my limited diagnosis skills I thought it may be the dist. belt but after removing the dist cap the belt looks fine.
I'm wondering what is the logical next step as after reading as much as I can it seems this could be anything. I do have a copy of Auftragsnummer 964 so I can refer to it for a detailed explanation.
Many thanks in advance.

deep_purple

Hi Dave,

You are right, it could be anything. However, I'd start with the simplest/cheapest potential fix and then go up:

1. Reset the DME by disconnecting the battery for a half hour. Let the car idle for a few minutes and then go for a spirited drive.
2. Replace the DME relay with the 993 part number.
3. Check the battery while idling and after a drive to see if the battery and the alternator are OK.

For me the key question would be the following: Does the hesitation still exist after the DME reset? It not the problem may be occurring as a result of "learning" based on a bad signal from one of the sensors.

Edited: One more thing. Adrian suggested that I might've had a vacuum problem in this thread.. It may also be worthwhile to check.

Hope that your troubleshooting doesn't take too much time and that the fix is a simple one.

Cheers,
ST

Adrian

Dear Dave,
Is your foot flat to the floor? This could be a simple adjustment problem with the Wide Open Throttle microswitch. One way to tell is to line yourself up on a clear stretch of road. Starting driving keeping the rpm as low as possible in 2nd gear but moving forward and not labouring then put the pedal to the metal. See what happens. Does it hesistate and then suddenly pick up and go?
The two areas are the WOT and the reasonance valve. If you have a vacuum leak (minor not major) this will also cause the symptoms. This hesitation is an indication of a failed headlight adjuster bellows by the way (if installed of course).
Ciao,
Adrian
964C4

Series 900

You may also have a worn carbon track on the barn door AFM.

Wikkid911

Thanks for the replies guys.

I have driven the car again this evening with the hope of isolating the problem. To add confusion to everything, it did not seem to start as well as usual and was erratic on tickover in the beginning.
Adrian, I have tried as you suggested driving the car in 2nd gear at about 10mph and then flooring the throttle. The car does not immediateley take off, it is not a smooth take up of power, its like it tries to get going and then after what is only a second or so the car then launches toward the red line. I tried this a number of times with pretty much the same result nearly every time bar one. Once the car is under full power it seems to drive well. From this result would you now look towards the WOT and the reasonance valve as suggested or the headlight adjuster bellows ??
I can try the DME reset this weekend if this will help the situation.
Thanks in advance.

Wikkid911

Very pleased to report that the replacement DME Relay has cured the hesitation problems I was having. From very low speed in second gear flattening the accelerator seems to make the back of the car squat down before it more or less immediateley launches forward. Tick over is now very smooth and the car will react almost instantly to any throttle inputs.
For the price of the relay ( £18 ) I should have changed this part ages ago!!!
Anyway, thanks for the help, much appreciated.

adewatson

Dave

I did the same this week £18 from Berlyn Services arriced next day took 2 minutes to fit, job done. Now runs like a dream

Adrian

Syd B.

I had a starting problem reported here last week which eventually was traced back to a faulty DME relay. I had a spare which I tried, however, as it turns out, it was also faulty. Had it not been, it would have saved me $80 for a tow. My mechanic didn't charge me anything for the fix as he sold me the faulty spare DME relay to begin with. New relay and all is wonderful in Porscheland again.

It seems to me that the DME relay is the root of a number of problems with our cars. Does anyone know just how one of these little buggers goes bad?

Colin 90 C2

I can't remember where I heard it or maybe I read it somewhere but it seems that the solder on the DME relay circuit board is is put on very thin due to the nature of electronic circuit board soldering machines.

the solution was to resolder the board by hand soldering methods and add solder to the traces thereby dissipating the heat of the relays.

I did this method on my failed DME relay and it has been woriking perfectly since (almost 9 months).

However, I still carry the spare relay in the car.

Wikkid911

Update on this problem - (for those with similar issues) - which is now fixed

The replacement of the DME did work, temporarily, but the problem always returned. The cause turned out to be the Air Flow Meter which was removed, cleaned and replaced. The car now runs like a dream, picking up from low revs with no hesitation.