[Gary Collison]

My CLK has picked up the annoying tendancy to "serge" while idling at a stop light when not totally warmed up. If you're not on top of it, the torque would rear end of the person in front of you. I get no error codes indicating there is a problem. It also seems that the transmission does not want to downshift when accelerating. I am at a bit of a loss. The car just turned 90,000 miles and I have not seen this before. Ideas?

 

[QuoteWarz Insurance]

The surging could be several different things, but one of the first things I would check is for any possible vacuum leaks. Lets the car idle and look under the hood and listen for leaks. If you can hear anything then mess around with the vacuum lines and see if the idle changes at all or you can use soapy water to find it as well.

If it is not a leak then it could be numerous different things, but I would suggest pulling the codes and see if anything comes up.

 

[Klaus9000]

On a cold start the RPM goes up for 30-60 seconds, when all parts are up to operating temps, the RPM drops to your normal idle(about 900 RPM). The question is, when you start it cold, how long does it take for the engine to settle down, should not be more than 2 minutes.

I would assume Mt. Hood is very cold this time of year, is the car parked outside or garaged? If you let it warm up, will the car behave normally OR do you just cold start it and hit the road?