Every time I depress the clutch and allow the engine to return to idle it stumbles and shudders. (Same thing occurs when sitting still and just revving the engine). It is as if the engine wants to stall, but at the last second the idle control takes over and keeps the engine running. It does settle down and idle smoothly, but it is that transition that is really rough.

The motor mounts are new, so that is not it. I have fiddled around enough to have that ruled out as the problem. I am thinking it is one of the following. Would like to get a second opinion before I start digging deeper.

1) Idle speed control
2) Air flow meter
3) injectors
4) vacuum leak
5) something else

Any one else go through this before?

Thanks...

 

Well, if it was an early car, I'd say it could be this -

http://frwilk.com/944dme/shudder.htm

Sorry that doesn't help much with your car...

Good luck,

Dale.

 

I have the same problem. If you figure it out, please post the solution. A lot of people here have the same issue but never post how they resolved it.
a search turns up a bunch of open ended threads.

 

Wow! That definitely describes my problem. I wonder if this didn't also carry over to my 85.5? I did replace the DME a couple of years ago. The original (I assume) DME developed the dreaded - no revs above ~1600 problem.

 

i got 85.5 with the SAME problem.. please let me know if you find an answer scott

edit- although i was before this, thinking along the lines of air regulator.. because if i am correct, the point of air regulator is that its a bypass of teh throttle body. The air hose comes before the throttle body, to the idle regulator, then directly to the back of the intake manifold. This is supposed to supply the right amount of air to keep the idle where it should be, especially when the throttle body cuts off all or most air. This is suppoosed to keep the engine from dropping much below idle, or at least i thoguht.

 

Hey, my 951 does that too! It didn't use to though. It's possilbe I introduced it sometime when I took the intake manifold off or any of the other times I fiddled around with stuff in there or it's doesn't like the warmer weather. Either way, I'd love to know a fix to it.

 

My 951 has a similar problem now ... my mechanic recommended that I replace the O2 sensor. I have a new one in a box at home. If it works I will post it on here ... although the results could be misleading because I am currently replacing all of the vacuum lines under the intake manifold (including the ones to the ICV). Either way, I will post an update when the job is done.

 

Don,

Maybe you could make one fix at a time - then test the engine to see if you get the desired fix. I know it's always nice to take care of everything while you're "in there". Anyway, please keep us updated.

 

I can do that. I'll hold off on the O2 until I get it back on the road. I'm not sure when I will get it finished ... time is something I do not have a lot of. This whole project started out to fix some braking issues (my dad's Chevy truck could stop quicker than my car). I made the mistake of jumping into buying new parts without doing all of my research (ie: my car now has a new brake booster ... real culprit looks to be a loose vacuum hose at the venturi valve).

Anyway, I got the booster in last night. MC and vacuum / boost lines should be replaced this weekend (I hope).

 

O2 sensor could be messed up being so old... (and it's cheap to fix!)
I replaced that and the AFM on mine, and it runs a lot smoother now.

 

Mine shudders, my mechanic thinks it is the balance shafts out of whack. If you rev it it drops to about 700-800 RPM then it shudders it's way back up to 900 or so and stays.

 

Scott et al.

I've been having the same symptoms in my 83 and replaced the O2 sensor and a cracked vacuum line but the problem was still present.

Browsing through the Workshop Manual in Clark's Garage gave me the idea of replacing the fuel pressure regulator and the stumble is now gone. I replaced the fuel damper also, but doubt it had any bearing on the improvement from what I've read.

FWIW, the unit was original on the car with 211K miles.

 

FRWILK has a compromise fix for the early cars on his web site. It's easy and takes about five minutes and it works. Just go to frwilk.com menu site.

 

My quest did it. (before the rod went thru the block...yesterday)

It was the FPR and injector clips

 

OK - it seems the fuel cut is the culprit. By resetting the idle speed set-screw it is possible to bypass it. Counter to the procedure outlined at frwilk.com (for early 944, at least), I turned the screw in to get passed the fuel cut "click". I backed the screw out enough to keep idle at about 950 (as indicated by the tach). The only obvious difference is that the engine speed gradually falls to idle at closed throttle. Since the fuel cut feature is no longer active, engine rpm does not drop instantly. The brief test drive has me optimistic. I'm confident that this will be a satisfactory compromise. I expect fuel economy will suffer slightly. But the elimination of the stumble will be worth it.

Where's the smiley for "your mileage may vary"?