A new issue has recently appeared. The engine starts as usual when cold (cold as in 80 deg LA), but then stumbles for maybe 10-20 seconds and clears up. It does not happen every time, and seems unrelated to the engine temperature. On one occasion, I drove to a store, shopped a while and then came out to start and the problem appeared although the engine was still pretty warm. The fact that it clears up so quickly upon a cold start does not seem like anything to do with a faulty DME temperature sensor; I don't think the temperature changes that much in 20 seconds, but maybe I am wrong about this.
What about a leaky hydraulic lifter that leaks down upon standing a while and takes a few seconds to pump up?
Any ideas would be appreciated
Thanks!
Wayne

 

A lifter would tick loudly but the jug would still fire OK, a little less valve lift but plenty overall.

Shut it down fast when it's starting to stumble, whip out the spark plugs and see if any are wet with fuel or coolant or the like. And observe the general condition.

Might be chewing on extra fuel from a leaking injector, FPR or damper. Pull the vacuum lines from the FPR and damper, run scrap line to some empty soda cans or the like and crank it for a few seconds. See if fuel comes out. This is not definitive, as they could still leak under vacuum. If you have a hand vacuum pump you can check with that.

 

Like he mentioned...I would check your fuel system as I had similar issues that turned out to be a failing damper.

 

Yeah could be a lot of things, check fuel pressure as mentioned. When is the last time the cap/rotor/wires/plugs were changed?

 

Since it happens at start and lasts for only a seconds and then runs beautifully, I don't think it could be anything like rotor, cap, etc. These problems would affect running all the time. On the other hand, the FPR could be the culprit, as suggested above. As far as I understand, it is a simple vacuum operated valve, and if it was "sticky" it might cause an over rich condition for a short time until it opens?
Jfrahm, I have a hand vacuum pump and will play around a little tonight. I also have a new FPR that is easy to drop in.
Thanks Guys, I will let you know how this turns out.
Wayne

 

It's not likely to get sticky and cause a problem. Usually the diaphragm leaks and fuel leaks into your vacuum system. Damper, same issue.

 

The vacuum lines to the FPR and the damper dont have fuel in them. Just before the problem began, the car sat for a couple of weeks (maybe 3) without being started. I have been driving it daily, and the frequency of occurrence seems to be decreasing.

 

Do you have any updates here? My 944 (happens to also be 1983) is experiencing the same issue, sometimes at cold start the engine RPMs will shudder between 400 and 600 RPM for a bit and then the issue will disappear after less than a minute and the car will idle normally

 

Same suggestion, shut it off right away and check for wet plugs, wet vacuum lines, etc.
Could be chewing on excess fuel and if so you need to figure out where it's coming from.

 

Rough cold idle are most commonly caused by a faulty DME temp sensor, but if its temporary not sure. As Jfrahm mentioned, it could be fuel related as well (fuel pressure test recommended).

Here are some suggestions:
https://www.clarks-garage.com/shop-manual/ts-01.htm

 

Still working on the problem. I am stalled until I replace the thermal fan switch which just died on me. I will be back on it next week. I am betting on something related to the fuel pressure regulator.
Clarks Garage is a gold mine for 944 owners!