Hey guys I'll start with a little back story on why this problem is a little wierd. This winter my truck 97 f-350 with a 5.8 351W decided to run like crap and was diagnosed with a dropped cylinder (compression reading on the cylinder was about 26 psi compared to an average of between 75-130) They said that it would need a new engine so we decided to drive it home and wait to collect some money first. During this time when the engine would run it would violently shake the cab and only run if you kept on the gas. I was told by a few mechanic friends that it sounds like a stuck exhaust valve. So we let it sit for the winter and today I decided to attempt and move it to mow the grass. I started it up and it ran fine, well almost fine. If you put it into gear it doesn't like to rev very low and after being in gear and going to neutral it revs up quite high I'm not sure how high cause i don't have a tach. Once put back into gear it will go back down but idles at around 25 to 30.

My question is if the engine did have a stuck valve how did it manage to fix or at least make better it's self, and what are some possible reasons that it's reving up when put into neutral

Any comments would be greatly helpful and I was planning on rebuilding the engine this summer if it still was acting up.

 

Maybe a stuck lifter that bled down while sitting. Maybe do an oil and filter change and refill with a high detergent motor oil untill the next change.
As for the high idle I would check for a vacuum leak.

 

alright thanks, i'll give that a try and post how it goes