• Welcome Visitor! Please take a few seconds and Register for our forum. Even if you don't want to post, you can still 'Like' and react to posts.

Sudden RPM Drop Confusion.


New Member
Oct 14, 2011
Reaction score
New Jersey
Vehicle Year
Make / Model
Engine Size
V6 4.0L
Hey everyone,

This is one of my first posts, but i've been lurking for a while.

Just got a 94 4x4 4.0L V6 Manual with 225k.
engine runs strong, however, There is a moderate leak in the passenger side valve cover.

While coming out of a stop into 1st gear today, the engine suddenly lost significant power, and hitting the accelerator didnt raise the RMPs nearly as much as it should have(Maybe a miss fire?). i had to drive for a little while, and by the time i got to a suitable place to stop, the engine was smoking from the area around the leaking valve cover.

I pulled over and shut the engine down. A short while later, i started it up to move it further out of the way of the road, and the problem was gone. Hasn't returned all day.

There was a loose vacuum hose to the air filter which I put back on, other than that, nothing changed. I don't imagine one loose vacuum hose would be the culprit, but maybe it was?

Could it be a fouled Spark Plug from the oil leak? or loss of pressure due to the leak?

If anybody has any suggestions or info, i would appreciate it. This has me very puzzled because it was a one time thing, and i cant diagnose the problem if its not doing what it did.