When my 87 944 is at idle I have a very bad shudder/vibration. When I give it gas and the rpms go to around 1100 the car is as smooth as silk. I have only had the car a few weeks so I don't know much of the history about it. My first take is that possibly the balance shafts are slightly out of adjustment. But I also notice that the idle RPM's fluctuate between approximately 800 to 900 rpm (constantly when at idle) This could possibly be a bad Idle Stabilizer. What do you think?

 

I picked up an 86 944 and have the exact same problem.

I've done the following with NO improvement:

Engine Mounts - changed with aftermarket units
Plugs/Wires/Cap/Rotor - all changed / new Bosch
Air Filter - Mahle factory filter
Alternator/a/c belt - replaced
Balance shaft belt - alignment checked and retensioned
Timing belt - checked OK
DME temp sensor - replaced
Throttle body - cleaned out

WTF?? My 88' turbo S ran like a turbine. I'm not sure what's going on here......

 

idle speed should be like 950 or 1000, it is silky smooth there.

lower speeds it will be rough...just raise the speed.

 

prob two seperate issues

idle fluctuate = either idle stabilizer or there's a vacuum leak.

shaking = BS out of time, motor mounts, ....other possibilities.


i thought idle was supposed to be around 800 or so..

 

says on the sticker, either 900 or 950 +/- 50

 

My 924 has done it the entire time ive owned it when its under 800ish. I just did the belts and i can tell you that the balance shafts are perfectly aligned, so it just doesn't like low rpms.

 

My guess is also motor mounts, I had the same problem with my 924s, 944 & 951.

 

Motor mounts most likely. Classic symptoms.

Get OE (i.e. Porsche branded) ones. Better than OEM reportedly. Much better than knockoff cheapies on eBay, etc.

 

yea prob motor mounts. I have Victor reinz mounts and love them. Car is smooth as silk at idle!

 

My car is smooth over 900rpm. Under that it's rough.