i have replaced all the mounts except the motor/tranny mount. can that be causing the vibration and cause the rpm to drop from about 800rpm to 300rpm. this is has me baffled. If the O2 senor is clogged it will trip a check engine light wont it? thanks

 

had a o2 sencer that didnt work on our 98 neon and it didnt run rough...that was the down stream o2 sensor..on our 98 breeze up stream o2 sensor wires where cut off=not working and no rough idle..when a vibrates and runs rough at idle..more likely bent valves..quick and easy way to find out is do a compression test...if a cylinder dont hold compression ,means you have a bent valve,,in that cylinder,,

 

done a commpression test one was 150 other 3 was 150. so i have good ompression