For all of my fellow M119 power plant owners... I was encountering a number of strange symptoms that were not adding up. In some cases, some symptoms were things that are commonly attributed to bad wiring harnesses on these motors. It turned out to be a failing alternator. Here are the symptoms that seemed to progress:

1. intermittent wiper malfunction - would turn on/off for no reason
2. frequent tail light and running light failure
3. Instrument gauges fluttering (gas gauge) Speedometer not registering - then jumping back to life
4. intermittent high idle
5. aftermarket stereo amps cutting out
6. intermittent engine "bucking" at the application of throttle.. on-off-on-off very rythmic
7. wiper running at extreme speed and not responding to switch... I mean stupid fast motion
8. headlights, dash lights appear exceptionally bright - coincided with high idle (1100 rpm +/-)

The last 4 issues appeared most recently and seemed to be conneted to extended highway runs. (the symptoms showed up during or immediately after the run)

Took her in to my Indy Shop..... veteran tech immediately diagnosed as a failing alternator. said to check the running voltage at the battery ..should not be above 14.5.

I had no voltage warning light and my car does not have a CEL. Upon checking the voltage, the reading looked normal until I revved the car high and things seemed to spike.

Replaced alternator and things seem to be in harmony.

.....perhaps this is a known series to symptoms to most but it was all new to me. I have never had an alternator begin to fail like this.

Hope this helps.

__________________
Jeff
'87 300E
'92 400E
'06 ML350