[V8] rough idle and when engine has reached proper running temp.

[dsaad at icehouse.net]

Wow -
this sounds a lot like the issue I was/am? having.  I put in a new fuel
filter and O2 sensor and things got much much better - but I still get the
occasional lag off the line.  I have not seen it in a few weeks now
however.
I can tell you for sure that these motors are very sensitive to the O2
sensor - and the sensors become contaminated very easily due to their
location.  If yours has oil all over it, it may not perform as it needs
to.
After a new  fuel filter and O2 sensor, (and assuming you have already
confirmed the ignition is all up to snuff) My next guess would be fuel
pressure regulator - which is easy to test, and then a fuel pump that is
maybe starting to go.  That is what I suspect now for my very intermittent
problem.


>
>  Hello.  I have q 1990 v8 4.2.
>   Recently put the motor in and its a good motor. When i start the car
> when the engine is cold it idles perfect and is very responsive with the
> accelerator. Once i drive it for about 20 minutes and the car has warmed
> up, it is the opposite. Idling a little too low and when i press down on
> gas pedal she hesitates a bit and there is a brief second it almost
> feels like a miss. Once i get the car up to about 30 mph it is fine and
> runs perfect. Only happens after car warms up and at idle and leaving
> stop signs and such.
> What does this thing have for a choke?
> I was thinking air filter or fuel filter or oxygen sensor but it operates
> perfect when cold so im stumped?
>      thanks
>   Chris
>    1990 v8 4.2
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