This thing has be baffled. "94 S500 with 75K miles belonging to an elderly widow friend. I have been doing routine maintenance for the past two years. Last week while changing the AC blower regulator she tells me it has been stalling at times. Sure enough I eventually got it to act up. It appears to be going into limp mode. The throttle actuator is unresponsive until you reach the mechanical part of the throttle. I have ruled out the MAF and today while having a closer look I notice it occurred when the two aux cooling fans switched to high speed.
I'm thinking the added current draw created a low voltage so, I tried to duplicate it by turning the headlights on and rolling all the windows up to the stop at the same time. I could not make it fail doing this. Only when the aux fans go to hi speed.
Turning the engine off and restarting will reset it back to normal until the fans go to hi speed.
The M119 runs fine otherwise, never gets above 80c, seems smooth...

I'm stymied.