rmoleman

I posted this last week. Everyone thought it was the balance shafts, but they check out fine.

https://rennlist.com/forums/944-turbo-and-turbo-s-forum/367398-help-high-vibration-at-idle.html
86 951 bought with 45k mile currently 58k (one owner car)

I did a bunch long term maintenance since I bought the car 12 months ago:

New timming belt and rollers
New water pump
New motor mounts
Replaced most of the gaskets in the exhaust system to fix multiple leaks
New plugs
New wires
New distributor cap and rotor
New fuel filter
New Pads
New Rotors
Changed brake fluid

It pulls strong, no oil smoke, almost zero oil consumption but there is one problem.

Lots of vibration at idle. The idle speed is correct and stable. As RPM increases the vibration is less but it can still be felt when driving. There does not appear to be any misfire and all the plugs looked good when I changed them.

Any ideas on what to look for are appreciated.

_________________________________________________________________
Checked the balance shaft alignment this weekend and it is perfect.
Pulled out the AFM and it tests good.
Inspected the motor mounts, they are fine
Pulled the injectors and tested
The injectors look like hell but they all spray fuel. I ordered new ones anyway.

Is there anything else I should look at that would cause a lot of vibration at idle?

minas

why don't you double check the balance shaft belts and cam belts?

400hp944

Motor mounts are comon issue, but since you have replaced them I would put your car up on some stands or a lift, start it and crawl under and listen. Please be safe!
It sounds to me like something is rubbing or hitting somewere. Is there a grinding sound?

Slider 951

You did'nt mention whether or not you did the balance shaft seals. If you did, make sure the gears are correctly oriented on the balance shafts. They have two keyways in each gear, the upper shaft uses one and the lower uses the other.

turboted

Coil??

dme

get your injectors cleaned and tested at WitchHunter. I had one injector that was off by 10% from the others. Replacing it really smoothed my engine.

rmoleman

Finally after replacing a bunch of stuff (which probably need replacing anyway) I found the solution on Clark's garage.

http://www.clarks-garage.com/shop-ma....htm#cold-idle

"There was an inherent problem with the early 944 DME programming (pre-1985.5 US/Canadian models only). These cars had a momementary fuel cutoff when the throttle was released from any throttle position off idle. However, the tendency was for the idle to drop too low before the fuel cut back in resulting in an idle shudder. The problem seems to be more noticeable on some cars and on others does not appear at all."

The fix is easy; set the idle higher and bypass the TPS. The idle is now stable when cold and hot (no vibration). It is a little higher then I would like when warm (~1000 rpm cold & ~1200 rpm hot). I can live with it.

Anyone else have this issue?

Wraith1027

I do. Though I just got the car, I have noticed this. Thanks for the info! I am where you were, I just got the car. 48k and has been in storage for years. Lots to do....and learn.lol.

turbo8

did you put in aftermarket motor mounts? they tend to vibrate alot more than stock

DM1

See if you carn raise the engine with a jack so it will NOT sit on the motor mounts (about 1/2 inch or so). If the car still vibrates then mounts are OK.