My 94 E420 had been having drivability problems. Symptoms were "hiccupping" at speed (like missing or bogging sensation) and nearly stalling on occasion at idle. Tried to use the cruise control and hiccups got worse. Using this fine forum and my mechanic, we formed the opinion that the throttle actuator was bad. The car has 170K on it.

I got a used one for $275 (!) and had it put on, but before I can gloat about that low price, the car is still not running properly. The new symptom is a surging at idle and hard shifting as if motor is going too fast at each shift. This is according to my mechanic as I have not been over to the shop yet to see it for myself.

Since the new problem is essentially the opposite of my old problem, I hesitate to blame the replacement part. Rather I read that possibly the throttle stop position must be relearned. I was not clear if this was necessary on a throttle actuator replacement as it apparently is on an Air Mass Meter replacement, but I presume that it is. As a precaution, I had my mechanic leave the key in the "on" position for a couple of minutes to see if that made a difference. It did not.

Is there anything that must be done by way of the scanner when replacing the actuator? Should I have all the limits reset to the base parameters and then drive for several short trips? Or should we raise the white flag and go to the dealer. Both my mechanic and I want to learn from this, so we would prefer to work on it ourselves before the dealer gets involved.

I should mention that he believes his scanner can do whatever is necessary, but he is not sure he knows how to get the scanner to do all that. He can pull codes and the like with it, though.

Any input would be appreciated.

Heymon