When I let off the throttle without shifting out of gear and I’m in the 3000-4000 rpm range, I always get a few loud pops coming from the exhaust when the car is slowing down. It will happen in any gear that I’m in. When shift into neutral and letting the car coast I don’t get that popping sound. Just want to know what could cause this? I was thinking it was backfiring.

 

Backfire for sure. Seveal things can cause it. When i was getting it my car i changed the AIR check valves. I dont' get it now anymore.

 

Could bad plugs cause backfire?

 

If it was the plugs you would have an engine miss. You could also have an exhaust leak somewhere in the system and it is sucking in cold air causing the popping.

 

yep, i believe so.
changing the plugs can't hurt n e ways, good way to tune up your engine

 

wait, my bad, rob is right. bad plugs is misfire, not backfire.

 

Does it still do it after the car is warmed up? Mine has the popping when the engine is cold ...so do many people I believe, its normal when cold.

 

It will happen when it is warm.

 

My car would do that when it was running rich. Since I've been playing with the programming (and fixed the fuel pressure regulator), it hasn't done it. Just a nice smooth deceleration note.