91 chevy V-6 rough idle and rough running

[mabbott]

Yes i have a 1991 chevy c-1500 with 130,000 miles and it has always had a rough and low idle. Idle is around 450 rpm. It also runs bad going down the road. The engine has intemitted pinging while traveling down the road with just the load of the truck worse when going up hills. I would consider it predetanation but cannot confirm it. I bought the truck from a friend of mine who replace the valve seals himself and was wondering if maybe he has the valves to tight if that is possible. I have a fair knowledge of working engines but not to well with computer controlls for automobiles. Any help would be greatly appreciated.