Goofy idle

The other day my friend and I were just letting his car warm up and it went to 2000-2500 rpm for about 10-15 seconds and then the idle began to fall. It climbed back up a little, we heard a loud pop (sounded maybe like a backfire) and the idle quickly fell again, only to climb back up and make another loud pop. After each pop it got a little lower until it hit ~700 rpms and it just held steady. Is this bad and what could be wrong?

From what I have gathered, it is the Idle Speed Sensor that seems to go bad on dsms. Mine kinda does the same thing....without the popping. It seems like your car is making itself backfire..check your plugs..see what is building up on them. If nothing....use a 12guage and pop something back at the car :screwy:

Ok thanks, not sure if its a backfire or not, it just pops. It is running open downpipe and sounds a little different than when it had the full exhaust on.