I hooked up an inductive timing light to each plug wire. I noticed that on cylinders 2, 3 and 4 the light seemed to have an erratic flash. All cylinders on the left hand side had steady beats as well as cylinder #1. Does this test mean anything? My test is not very scientific, the timing light could be too sensitive or I could be imagining things. I have new Beru plug wires installed. I've been investigating why the idle on my 89 560SEL is a little rough. I haven't rulled out a vacuum leak or fuel problem. BTW, the timing at idle appears to be 12 degrees BTDC. Shouldn't it be more like 4 degrees at idle. Is there a better way to measure the timing advance on this car? The timing chain was replaced recently as well.

I've ordered a new coil to see if that helps. I don't really want to solve the problem by swapping out parts but since it looked like the original coil and I plan on keeping the car for another 100K miles I don't mind in this case.

Thanks
~Dave