420SEL ACCELERATION HESITATION

Hi, I have a 86 420 sel,all of the sudden it developed a hesitation upon low rpm acceleration, runs fine above 1500rpm.
have had car to two shops @ $900.00, they have swapped all control devices /relays(with another 420 in shop)new wires/plugs/fuel filter/injection system cleaning/adjusted idle i think/adjusted throttle body/new motor mounts/new cap@rotor,
last shop said good spark to cap from coil, bad spark out of cap to plugs, remember new cap/rotor/wires,distributor seems fine it advances 20 degrees and back to 12btdc,new plugs gapped at 32thou,compression on all cyl is above 150 psi.
we are totally puzzled, any ideas ???????
what is secondairy voltage breakdown on a coil?


update: after reading other threads I decided to check the coil, the dealer said it was fine(they charged me for checking it) anyway it was supposed to read .3 to .6 ohm it read .6 and faded to .1 after about a minute of holding the meter on it. I will replace coil and see if the $900 was all a waste. IF IT WAS FOR SHAME ON THE DEALER AND THE OTHER SHOP WHO SAID IT WAS FINE!!!!!!

[Edited by TIM PAULUS on 02-03-2001 at 09:12 PM]