Hi anybody who could help. I own a 1998 mercury mystique 2.5 V6, 156,000 miles, lately everytimeI turn on the A/C on the car; will star shaking, I Have noticed that the automatic tensioner will vibrate, it seem like it will not compensate rpm, at idle the engine shakes (do not stall) I did change the tps, nothing change, I was wondering if anybody knows what it's that makes the car compensate rpm once the A/C is on, this car at idle shows 800 rpm, at 1500 rpm all shaking will stop but once the car it;s at a stop or normal idle the shaking begins, any help will be appreciated, thanks