My 94 Accord LX 4cyl with A/T (140,000 miles) idles a little rough at normal idle with the A/C off. When the A/C is on the engine really vibrates noticeably when the car is in drive with foot on the brake - putting it in neutral will smooth it out a bit). Otherwise, it seems to run fine with good pick up etc. I'm inclined to think it is a bad motor mount, but not sure which one it might be. Does anyone have any suggestions as to the cause of this vibration or the best way to troubleshoot? Thanks in advance for your help!

 

Good question... I recently did my AC and im noticing that my idle is kind of rough too... I know its not my motor mounts but any ideas would greatly help...

 

It's not "normal" per se, but it is very common - probably about 70% of the '90-97 automatic Accords that I've driven will do this. I believe it's caused by a bad rear engine mount - the $290 electronic/vacuum-controlled one.