supes6

I'm having a problem with the car where it will stumble/hesitate during the first couple minutes after I start the car. It seems to get worse as the air temperature outside gets colder, or if the car's been sitting for a few days. When it's really bad I have to rev the engine to get going in first gear and then it will hesitate if I try to go anywhere past half-throttle or so. After a mile or so of driving the problem goes away - before the car is even up to normal temperature.

So far I have replaced/fixed the following:

-plugs, wires, cap + rotor
-TPS
-vacuum lines and venturi delete
-BPV
-cycling valve
-intake gaskets
-injector seals
-DME temp sensor, wiring tested ok
-reference sensor harness
-swapped out different AFM
-new crush washers on KLR fitting
-tested ISV to be working

Someone said that it could be the fuel vapor purge switch.. I checked mine and both of the connections are intact, but I remember there being a minor leak when I did the vacuum test. Is it possible the switch could be stuck open and would that cause the hesitation I'm having?

Is there anything else I should be looking at?

Lizard944

I don't want to "speak" too loudly, but this can sometimes be the sign of a leaky head gasket. Do a search on tests for checking the HG. One way is to go for a drive at night, park the car then quickly relieve the coolant pressure by opening the bleeder screw, then CAREFULLY remove the expansion tank cap using some heavy rags. Start the car in the morning and see if symptoms improve. If so, you may have a slow leaking HG which dribbles pressurized coolant into a cylinder.

supes6

Thanks.. I'll check that out tonight.

bendavis2

It seems like there was a similar post a week or so ago and there was some suspicion of the Fuel Pressure Regulator, Fuel Pressure Damper, and possibly a gunky Auxiliary Air Valve. See link below:

https://rennlist.com/forums/924-931-...runs-fine.html

KuHL 951

I just went through something similar. My 951 would always start fine, then stumble and idle rough. Once it was running for about 60 secs it would run better but still had a slight lope in the idle. When it failed smog a few weeks ago I tracked it down to an AFM flapper door that would not close completely against the stop, especially when cold. A spare was installed and the car now has easily passed smog and runs the best in years. My old AFM turned out to be a 'remanufactured' unit.

supes6

I just swapped the AFM with a low mileage one from an 88S.. didn't change the problem. Guess I'll start looking into the FPR and maybe a leaking injector.

Also, what exactly is the auxiliary air valve? Are they talking about the ISV?