Brief issue immediately after cold start

[notMyScreenName]

I have a start issue that I have not so far been able to diagnose and would greatly appreciate any suggestions as to what to look for...

The engine cranks fine and starts after a second or three of cranking. It very briefly runs correctly, probably less than a second, and then immediately starts struggling to keep running. It struggles for maybe 3-10 seconds and then idles fine. After that I can restart the engine without problems. The engine otherwise runs fine.

I know that the idle switch, DME temperature sensor, air volume and air temperature sensor are all fine and the ISV seems to be OK - I don't think that it is sticking (if it is, it is only doing so at cold start, and I recently bench tested it) and it is being correctly driven by the DME. There are no vacuum leaks that I can find (I've pressure tested). The FPR and FPS are both relatively new (the FPS diaphragm had failed so since they were both old I replaced both) and the fuel pressure seems to be fine.

I've been on and off looking for a solution to this problem for quite a while now and thought that maybe someone here could point me to something that I'm missing.

Stock '87 951.

Thanks!

[mytrplseven]

I'm wondering if your fuel pump check valve is leaking all of the fuel it's supposed to trap in the fuel line, back into the tank and It takes a minute to resolve it. One way to check this out is to jumper the dme contacts (see Clarks Garage for this info) for a minute to "Charge" the line and then take the jumper out, replace the relay immediately and then start the engine. If it starts fine, without any symptoms, I think you're there.

[notMyScreenName]

Thanks . I'll try that.