wierd idle/hesitation

[mike87mj]

so mytruck is a 87 mj 4.0 2x4 and it has just recently started to get a rough idle and feels like hesitation when starting to drive. this only seems to happen once the truck is hot. and its not a over heating hot just normal operating temperature. if i really get down on the gas while its doing this it seems to sputter at first and then will accelerate like nothing is wrong and while driving it seems fine but as soon as i hit a light or park the rough idle returns and the hesitation when i go again. if i park the truck for a while and it cools down the problem is gone untill it warms up :dunno: now iv done some lookin around and looks like i might need to do a valve cover gasket but other than that everything looks fine. a valve cover gasket wouldnt do this would it? any ideas?

[Wildman]

If you can, do a fuel pressure check on it, it sounds like after it hits operating temperature it lacking fuel feed, almost like a vapor lock.

 

Here's the test and spect's on the fuel pressure -

 

http://www.lunghd.com/Tech_Articles/Fue ... ostics.htm

 

Another thought.........

 

http://www.lunghd.com/Tech_Articles/Eng ... ostics.htm

 

The valve cover leaking should not have anything to do with a vacuum leak, or rough idle.

[Mongo]

:agree:

Had the same thing with an intake manifold leak.