951jamie

I have seen the shafts installed on several occasions,the gears have 2 marks on them,most people use the same mark both upper and lower which is incorrect.also to check for vacuum leaks by GENTLY spraying some starting fluid around the vacuum hoses, if you get an increase in idle you have found your leak.
Good Luck!
Jamie
http://www.944online.com/techinfo/

Scott at Team Harco

If this problem is new and no work has been done to the engine - the balance shaft idea is a dead end.

Here are my thoughts on the most likely causes:

1) Motor mounts. These wear out over time. Cold may make the viscous fluid in them less compliant and therefore transmit harshness thorough the vehicle - especially at idle.

2) Engine control problem. Idle/air control, coolant temperature sensor, etc.

3) Vacuum leak. This should be easy to find and remedy.

The only way it might be a balance shaft issue - is if the belt has slipped teeth (not very likely). Unless, for some reason the engine ran rough before and it wasn't noticed.

aprotogerellis

Thanks guys - I'll start investigating this weekend...

968PORSCHE

I'd say check balance shaft marks first since that is easy. Is the car running rough or just viabrating? Determine this first. I had an injection problem that made mine shake at idle, but the car was having a very slight miss and all cylinders were not firing evenly. Turned out to be a bad fuel pump. so you could have FI or ignition problems. I.E. bad wires, plugs, rotor/cap. Open the hood and run the car in the dark and see if there is any arcing of sparks. A quick easy check.

aprotogerellis

Ok... checked the belts this weekend and although the balance belt did need tensioning, it didn't resolve the vibrations (as expected).

I spend a bit of time observing the rev counter and saw some potentially interesting behaviour:
The vibrations are still there though, loud and clear. I also observed the rev counter a bit more and noticed the following:
- It idles at 850 revs (i.e. just above the last minor mark under the 1000 revs major mark)
- When idling it occasionally goes up and down by 20 revs or so
- If I increase the revs to 1000 all vibrations go
- And now the weird one: If I apply any amount of gas (even so little that the revs increase is not visible on the counter), the moment i release the gas the revs will drop to around 750 and then increase to the normal 850. Is this normal?

Does this lend any further clues?

bbourdon

Fuel pressure regulator may need to be replaced.

IAC valve may need to be adjusted to increase idle.

Your throttle cable has stretched and needs to be tightened. (just a little bit!)

What weight oil are you running?

Scott at Team Harco

The mild idle fluctuation is not unusual.

Have you checked the engine mounts? This is a classic problem with these cars.

If that is not it - there is likely a spark or fuel imbalance problem at idle. Fresh plugs, plug wires, clean injectors, etc. may lead in the right direction. You may be able to isolate the problem if it is spark or fuel by pulling the plug wire from each plug (one at a time) to note the change. If it is a spark or fuel issue - you will notice less of a change when the bad cylinder is disabled.

I still think it is engine mount related. Please check that.

bbourdon

Fuel injector o-rings should be replaced and your fuel injectors should be cleaned.

Change your oil if not already done.

Check your motor mounts first, though.

The unL33T

I know this thread is very ancient but did you ever find out what your problem was? I have the same issue with my NA.

aprotogerellis

Hey! Wow, brings back memories

So, I did replace the engine mounts and it did get better. Its still more vibration at idle than in other 944s I've been in but unless you're looking for it you wouldn't notice

The unL33T

Thanks for the quick reply! Motor mounts were the first thing I tried when I got this car 10 years ago. Has had the same problem forever. I'm sure it's something easy I just haven't figured out yet.