Replaced water pump, now idle is fluctuating...
 

I had the water pump replaced yesterday - it went out while I was on the freeway.

I have a 1993 300E, with the 3.2 liter M104 engine, 134,000 miles on the clock.

Had it replaced by my MB indie, and when I pick up the car, the idle is fluctuating up and down. It wasn't doing this when I brought it in. It does this at idle in any gear - park, drive, reverse.

The check engine light is not on.

I don't know if there is a connection between replacing a water pump, and a fluctuating idle. Is there anything they could have touched or disconnected that could have caused this?

It "feels" like a vacum problem, so we checked to make sure all of the vacum lines were connected. They are.

Is it the mass air sensor?
Is it the throttle actuator?

Wouldn't these trip the Check Engine Light?

Is it just an amazing coincidence that immediately upon changing the water pump, I get the failure of another component?

Heeeeeelp.

There is a large black vacuum tube that could have been knocked off.

Well, the mechanic said he hooked it up to the scanner, and found codes for the air mass sensor and the coolant temperature sensor.

He explained that these two sensors communicate with each other and the DME, and that one or both could be out.

He replaced the coolant temperature sensor for free, said the problem didn't reoccur, so I picked it up and drove it home, when the idle immediately started fluctuating again. It fluctuates so much at idle with the transmission in drive, that I have to put it in neutral to stop the car from jerking. It's so embarrassing.

Called Edmond (the Irish-looking Syrian) back and he declared that it must be the air mass sensor. A frequent replacement item for all Mercedes- new and used - he said, and had a stack of 4 or 5 on his bench that he's replaced within a week.

Dealer wanted $447, fastlane charged me $255 delivered next day air - early morning delivery. Phil even kicked in $10.00 for the early morning delivery.

I love this site and the Fastlane parts shopping experience. I tried crying to Phill about my problems, but he wouldn't hear any of it - he's got a used Cadillac he bought recently that needs a new engine! Yikes!

We'll see if this works.