got 01 neon se 4 cyl. with 140,000 miles.about 5 months ago air intake hose cracked and had to be replaced. when it was first replaced, car seemed fine. but slowly over time has been giving me a rough idle at stops and in park.the rpms drop to about 550 to 600 while at a stop, and seems to be getting slightly worse as time goes by. seems to be worse when car in warmed. air filter is good,plugs and wires have been changed, upper and lower motor mounts have been replaced. ive been searching online, and was sure that it was the iacv, but after taking it off and cleaning it, their was no change. tried unplugging it while car is on, but car died out so not sure if it is a bad iacv. has anyone else had the same problem and has been able to find a solution?

 

Idle undershoot is to blame. I posted in 2gen about the same issue

TSB link is HERE

Joe