Stall and Rough Idle problems

[benji414]

I have a 1984 944 N/A that has recently been stalling and idling rough and has left me stranded twice. It starts and drives well if the engine is cold, but after about 15 minutes of driving, or when it reaches about operating temperature, the revs drop to around 800-1000, the idle gets rough, and the engine sometimes stalls when accelerating from a stop. Starting the car when the engine is warm takes wayy longer than usual and it sometimes doesn't start again which left me stranded. When I came back about 4 hours later and let the engine cool, it started up no problem. It occasionally jerks during harder acceleration in 2nd and 3rd gears, but for the most part, the engine seems to be running great in higher rpms. It seems like these problems are fuel related but I'm not sure. I already replaced the fuel pump, I checked the fuel injectors and spark plugs and nothing has changed. I was thinking it could be the FPR or a vacuum leak, maybe a sensor, but I wanted to see if anyone has had a similar problem and could share some wisdom.
Thanks, Ben

[maint]

I made a home made smoke machine (found a how to online) and found many small vacuum leaks. Ran much better (but not quite 100%) and sometimes wouldn't start when hot. I just changed out the reference and speed sensors and their wiring harness. Plugs on the sensors were falling apart but probably the worst were the shielded wires going to the DME. Wires had taken a tight bend after the rubber at the plugs and all wires and shielding were bad and cracked. Haven't had much chance to check the 'hot no start' but my idle is better. No slight surging on warm up that I tried everything to get rid of

[walfreyydo]

Sounds like a classic DME temp sensor issue. The DME will richen the mixture when the sensor is telling it the engine is cold, so if its malfunctioning, you will have rough running issues because the DME isnt getting the correct information. In your case, the sensor may be reading cold all the time, thereby causing rough running when warm.

This clarks page will walk you through the possible issues and how to test. The "car idles rough when cold" section can also apply when warm.
https://clarks-garage.com/shop-manual/ts-01.htm

[benji414]

I ordered a dme relay, plugged it in, and it drove perfectly. All of my problems melted away. Thank you for responding, that was the easiest fix ever.

[walfreyydo]

DME relay or DME coolant temp sensor?