500SL engine stumble and cluster wacky
 

Hey folks, I'm hoping someone might have some insight into this:

If I start my 1990 500 SL after it has been disconnected from the battery for awhile, both the engine and the instrument cluster are fine (ECU has been reset??). However after shutting down long enough to gas up, and restarting, the engine stumbles and stalls and the gauges go wacky. The tach will show lower than the engine is running, the fuel economy gauge bounces back and forth like a pinball machine, and the other gauges may or may not work at all.

If I do get the car moving (by not accelerating too hard) the speedo underreports my speed by about two-thirds. And the car will surely stall again at the first light.

Not the cold start sensor
 

Read elsewhere that it may be the cold start sensor. Disconnected it but no change. Anyone have any other ideas?