Low Idle/Vibration after Deceleration
 

New to the 944 world. I've had a 911 for over 16 years...just picked up my first 944 - good car - seems mechanically sound - runs well.

One problem / annoyance is the idle dropping very low / causing vibration after higher revs.

Say i'm cruising along at 2,000-3,000 RPM's - Slow down for a stoplight or something push he clutch the RPMS's drop well below 1,000 and the engine vibrates pretty good for about 1 second or 2 then recovers...it may just be its 30 years old and thats the way it is...but was curious if anyone knew of something else that might be causing it

its a 1985.5 944 - about 88,000 miles...lots of recent major service - new belts, ac compressor, PS pump, fluids, etc...

everything else seems good mechanically other than this annoying low RPM vibration.

any advice for a 944 newbie is appreciated

Thanks

Could be motor mounts... I know mine vibrates like something else right now at low, low RPMS. I just did the water pump and belts and the balance shafts should be aligned properly.

2 things i'd check:
1) is the throttle stop adjusted properly and is the throttle cable very slack?
2) does your car happen to have a 1982-1985 DME/AFM combination by accident? they had a built-in "idle shudder" like you describe which was corrected with the 1985.5+ DME.

had that happen in my 87 924S had to replace my throttle cable.

I'm going to go with a motor mount on this one. As long as you're sure the balance shafts are timed properly. I'd check that first though since it's easy to check.

Guys... Motor mounts wouldn't make the rpm drop.

How much "slack" should there be in the throttle cable? Mine was loose enough that it actually popped off the cam when i was farting around with it. Should it be that loose.

thanks so much for the help

Thanks for all the tips...adjusted the throttle stop just slightly...that did the trick...so far anyway..idles just a bit higher than before but doesn't bottom out like it was...will check engine mounts next time I'm under there...from my research that job is a huge pain.

thanks again

While on the topic - anyone ever used this? - Throttle Response Cam - Only944.com any benefit?

Quite a few threads here and over on Rennlist about it.

Short version: Buy it. Install it. Love it. Also, put in a 4-degree offset cam key (928 Motorsports sells them) the next time you do a timing belt change. Those two mods are pretty much universally loved, and you just can't go wrong with improvements that cost that little!