1994 Mercedes Benz C280 Base 6 Cyl 2.8L
Bouncing tach while in neutral and park
When in park or neutral my tach bounces up and down between 500 and (sometimes as high as) 1200. I can also (barely) feel the engine vary slightly while on cruise control at 60mph or higher and it matches this varied rpm pattern. Recently it started to offer a slight hesitation when allowing to coast to slower speed, like coming down the ramp off the interstate, then hitting the throttle again. Computer link showed everything from mass air flow sensor to a bad coil, so I bought all new parts. I keep this car in great condition so I replaced everything listed and what ever else I can think of, but I feel like I am playing "whack a mole". Anyone hear of this? Repair shops tell me to go to a dealer, but they are $250 just to take it for a test ride, never mind the $150 per hour labor.
Just got this problem fixed on my '94 C280 - replaced bad air mass sensor, which was causing lean running condition which led to surging (and several other codes, which went away when the sensor was replaced). Get the part at autohausaz.com (around $180) and have your mechanic install it. Worked for me!