Have a 91 190e 2.6 that quits running while driving down road or at stop sign and will not start back up. I have replaced the MAS Control Unit (fuel pump relay) which helped for a couple of weeks and then back to same roblem. Have also replaced ignition coil distributor cap, and rotor since reoccurence. Took fuel pumps off car and mechanic supposedly checked and said they were ok. Think I hear them running when turn on ignition. Have let car run at idle extended time on occasion. But when i try to restart it, may not start backat all for weeks or struggle to get started and rpm may surge up and down Help!

Get an old spark plug. Next time it won't start pull a plug wire (I helps to have the proper tool.) attach it to the old plug, ground the plug and have someone crank it while you check for spark.

It sounds like you're just throwing parts at it. This simple test should eliminate the ignition system or indict it as the culprit. Electrical intermittents can be tough to find. Check all primary and ignition system connections including the TDC sensor wire. That's what the EZL uses to time the spark - no TDC pulse, no spark.

Duke