Engine/Transmission (1998.5 - 2002) still a rough idle

[Ncostello]

Well, after changing the fuel filter, lift pump, refilling the tank with Performance Formula by Stanadyne, and refilling again with Stanadyne and Racor Biocide, I still have a ever so slight miss only at idle. The tach is steady. But I can still feel the truck vibrate and can hear the engine just dont sound smooth like it usually does. It only does it when warmed up fully. It does it at stoplights etc. If I let it sit for a minute or two like this it will eventually go away. It does not do it when cold. And if I turn on the A/C when idling, it will smooth right out, as if the extra load causes more the engine to inject more fuel and take it off idle. I suppose I will have to wait a while to see if the Biocide worked. Only thing was, the filter change looked really good. A little blackish but no grit or slime. ???

 

[AggieJustin]

Two things come to mind...



1) Check the IAT sensor. I read in an old post that a misreading IAT sensor can cause a skip at idle after its warm



2) A friend of mine had the same symptoms on his '99... . turned out to be the injector pump. Another injector pump killed due to a lift pump failure.



JM

 

[Ncostello]

Oh... and I also replaced the crank position sensor too. I'll check the IAT. The truck seems to run very strong otherwise and starts on the first revolution. The IAT is the one thing I did overlook. Sure hope its not the VP. If I have Schied take a look, can they spot a bad VP using diagnostic equipment??