[frankvan]

For the most part the car accelerates very smoothly except for two instances:
1/ from dead stop it occassionally stumbles at 1500 rpm. I've actually had the car stall once from this (on rail road tracks at that!). If I do a slow clutch slip start with revs above 1500 it doesn't stumble at all. But doing that all the time would affect clutch lifespan negatively...
2/ At WOT (wide open throttle) it will start to stumble around 5000 rpm - almost like the rev limiter kicking in early. If I ease up on the pedal just slightly it goes away.

I'm thinking it might have something to do with the TPS or idle/WOT switches?
(I'm not sure which variant our cars use for the Motronic).
I've checked for vacuum leaks, includeing the MAf to plenum boot and everything seems fine.

Car is a 91 S.

 

[jontg428]

I had this issue a long long time ago, and it could be many things. Mine turned out to be the AFM, but yours could be anything from poor ignition components, to a plugged fuel filter, to bad grounds. My advice would be to do the cheap stuff first, namely a good tuneup including plugs, wires, cap and rotor, and a new fuel filter. Provided this is done, then it could be the motronic temp sensor, or its connector, or the fuel filter basket is plugged, which resides in the tank. Just be sure the boot between the AFM and the throttle body is in good shape, take it out, shine a bright light on it, and make sure its good, as this seems to cause most of the issues. I learned the hard way, took it to the mechanic got the "its fixed" and after a grand later took matters into my own hands. I also suggest finding alfisti in your area that can supply parts, this is also very helpful, and there are lot so great people on this board that are willing to provide such help, if they have the parts. Don't give up on your car, I almost did on mine, but man, I just love my 164, worth the time it took to get her running right!

 

[frankvan]

thanks for all the ideas. I did just do a valve clearance adjustment (and they were all within spec since doing the last adjustment back in 2000!) and I bet I forgot to re-attach the two grounding straps on the passenger side of the intake plenum - because I remember that I forgot to that back in 2000 as well

And trust me I'm not giving up on my car. I've had it for 12 years and still love to drive it (even though my daily driver is a 911 C4 but it has the awd for the frozen north where i reside).
The sound of the engine is intoxicating compared to other things on the road (and a he11 of alot better than the clacking noise of that Porsche)
However, my 164 does have a Stebro muffler with the primary removed and an open cone filter (with a shield so it doesnt get all that hot air) so it does make a bit more noise than your regular 164

 

[drubie]

Check the little vacuum line at the back of the engine that's part of the oil vapour recovery system. On my car, this line was brittle and broken and had very similar hesitation issues (although it's an auto, not a stick).

You can replace it with small bore fuel line if your local parts shop doesn't have the right size vacuum line.

 

[grubs164]

The combination of those two symptoms suggests to me that there is a fuel supply problem. There would seem to be insufficient fuel pressure to properly enrich the mixture on initial acceleration, and insufficient to hold the higher revs. Check your fuel filter for blockage or restriction, and check to see if proper fuel pressure is being delivered to the injector rail.

 

[ChazzyD]

Remember that the fuel pressure regulator is operated by a vacuum line, so here again, vacuum leaks have to be addressed.
Charles

 

[frankvan]

Problem solved - bad main ignition wire.
FOund out by touching distributor lead while engine running
(won't do that again!).
Replaced with a generic Beru cable and it works fine.

Thanks for all the help guys!

 

[Alfisto Steve]

Problem solved - bad main ignition wire.
FOund out by touching distributor lead while engine running
(won't do that again!).
Replaced with a generic Beru cable and it works fine.

Thanks for all the help guys!

That smarts doesn't it?

 

[frankvan]

Sounds like you've experienced it too.
Best one I had was my lawn mower was misfiring and I saw the plug wire was loose - reached down to tighten (with engine running of course) and it knocked me on my a$$. Makes me out to be a perty smrt guy...(Darwinism? I'm still surviving!)