1993 F-150 5.0L 302 V-8 4x4 with Automatic trans.

My Truck runs okay at first but after driving and when it warms up, this problem occurs.
After I stop and shift to park, the idle fluctuates up & down between 450rpm and 1000. After fluctuating for about 20sec it steadies out at around 900rmp nice and smooth. This also happens when shifting from Drive to Reverse. Occasionally it will stall out when shifting from Drive to Park and/or Rervse.

This idle problem started after I installed a new tank fuel pump last week.

Do you know what may be causing the idle to perform this way and I what should check to correct the problem.

 

I recall there being a rash of problems with the aftermarket fuel pumps. If no-one else replies with a better answer I recommend using the warrenty on the pump. This sure sounds like a fuel regulator problem but I am not sure if the regulator is part of the pump on your model.

 

Thanks, but i'm pretty sure the fuel pump working properly since the truck runs fine other than described. Only in park and after driving til it warms up.
I was think more along the line of the throttle postion sensor or some other sensor.?

 

I understand, but keep in mind this is also after the pump warms up and in park when you are not demanding more fuel.
You did say that this started after you installed a new pump, did you make any other changes/adjustments?

BTW, did you change the fuel filter with the pump or recently?