Low Idle/Vibration after Deceleration

[mtc911]

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

[Chris944-1]

Originally Posted by mtc911

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.

[v2rocket_aka944]

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.

[Alexb944]

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

[dgcantrell]

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.

[v2rocket_aka944]

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

[mtc911]

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

[mtc911]

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?

[dmjames]

Originally Posted by mtc911

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!