Hi. My mk1 focus 1.6 zetec has an odd vibration issue. At normal idle the car is fine. No vibration what so ever. But when i put on anything electrical the headlights, heater, rear window heater etc. The car vibrates constantly at idle. The revs stay level and dont dip, the vibration is more of a pulsing vibration and the engine shakes. Ive cleaned all the grounds in the engine bay and used a multi meter which is showing zero resistance. Ive also checked the alternator using the multimeter on the battery and the reading is a steady 12.7 but when i start the car the reading pulses up and down with vibration and is between 14.0 and 13.5 and is not steady. The thing that baffles me is the revs dont budge but you can clearly see and hear the engine pulsing and vibrating. I dont think it could be the engine mounts as it only happens with the electrics on and its not a steady vibration. Im thinking it could be the alternator or voltage regulator. Any ideas would be great.

The readings from cold do seem a tad low it should be 14.4v 13.5 ide expect with tge electrics on saying that the battery is fully charged at 12.7v so it wouldnt need the full 14.4v there are a few common issues that can cause this one is the vacume hose to the throttle body which collapses and tge pcv valve which has a spring that goes weak check these first dont change anything without going to a dealer as you could change the alternator and every mount and have the same issue