is this when it is hot or when it is cold? The reaon i even ask is because i want to check them....simply because the engine was rebuilt recently by someone i dont know. The guy i bought the truck from either rebuilt it himself or had it rebuilt.....he had it bored out by a local machine shop to so all cylinders have about 180lb psi

Neways, when im driving it...it accelerates great sounds awesome...until i let off on the gas and leave in in gear. It pops and backfires and makes all kinds of nasty sounds unless i take it out of gear and then it idles right down. Any ideas wut it could be? I have heard that possibly poor valve job, but what else could i try?