94 E500 Idle Issues
 

My 94 E500 is driving me bonkers. Over the last year, the ASR light has been coming on and the car has gone into LH mode reguarly. However, it has always been controllable because if you turned the car off and let it sit for about thirty seconds, it would restart in normal mode. However, it started happening more frequently, and a month ago I took the car to my Indy to try to figure it out.

The car still had the original harness, so I wasn't too surprised when he noticed the fraying and decaying there. He said he couldn't diagnose the numerous fault codes he was getting without a proper harness. So we replaced that. Then, the fault codes were gone, but the car idles very poorly, and the timing swings from one extreme to another: about -20 to +20. After running like that for a few minutes, the idle goes down below 400 and the car eventually shuts off.

The Indy found a bad idle switch and problems with the throttle cable. Those were replaced, no luck. My man then concluded that it must be the ETA. So in went a rebuilt Beckman Technologies ETA. Didn't change either. Then I bought a used EZL (no easy feat) and we tried subbing that in, but it didn't change anything in the way the car is running. So now I have a spare EZL. The car remains undrivable.

So, question is, what would affect the timing so much that it does not remain steady and then drops the idle so far down that the car shuts off?