Hey Guys,

I have a 1999 996 C2 Tip Cabriolet. It has been in the Porsche workshop for 3 weeks now entering the 4th week. My mechanic has tried many things without luck, so I come to you for help.

The issue is, when driving along and keeping at a specific speed, the revs will constantly surge up then down. It does not do this under accellaration but only when you sit at a speed and keep the throttle constant to stay at a speed, for example 60 km/h or 100 km/h.

We thought the 80,000 km major service would fix this but it didn't. New spark plugs did not change anything. Spark plug coils were check and no issue found.

It already had new MAF Sensor in Jan but we replaced this again to be sure and the issue remains.

Engine was checked for leaks including vacuum lines etc using smoke machine and no issues found.

Transmission was serviced in Jan, oil changed. He has also checked the oil again and cannot see any issues.

It may be the transmission but he doesn't think is so due to the above and also that this surge can occur in any gear.

We are out of ideas, and I am losing patience, if anyone has any suggestions that would be great.

 

You should post this on Renntech. Loren might have an answer.

-td

 

 

In this case, it may seem harsh, but it's usually best to switch mechanics.

 

When the RPM's surge, does the vehicle speed up? If you get a change in RPM, but not in vehicle speed, that is probably a slipping transmission. If there is a change in speed, then you likely have a fuel system or engine control ECU problem. Do you have any fault codes? Have you cleaned the injectors? Checked fuel pressure?

I would suggest you take it to the dealer for diagnosis. Good luck.

 

im new to porsches but that sounds vacume or throttle position sensor related surging liek that on other cars is due to vacume leak and the motor trying to compensate for a different vacume then it should ahve at that speed

 

Thanks for the reply. The car is at independent Porsche specialist.

To answer your question mathism, no the car does not speed up. Initially we thought it was transmission but because it does it in each gear we did not think this is the case. But with all issues checked thus far I guess the issue may be transmission. This is being checked today. i will let you know the result.

For the record, they are only charging me for what they fix which is good.