when my car is idling...about 700rpm...there is a popping sound coming out of the tail pipe...my friend asays it is a piston misfiring?and when i am in 5th gear going about 35-40 mph and mash the gas my car will backfire...there is no smoke or anything....what is the problemmmalso my engine is a d16a6 in a 1990 honda civic si hb...thanx..

 

your timing is probably off.

smell the exhaust and see if you can smell a bit of gas..

 

actually i can smell some gas...so is it advanced or is it turned back.....

 

also my ecu isnt throwing any codes....what can i do....does after time the timing advance or retard, u know after wear..?

 

Check your valve lash and compression as well.
Just a thought.