2000rpm warm idle on 190E 2.3 8V (1993)
 

I have had my 190E 2.3 8V for almost 4 years, and it now has about 188K on the clock. A few weeks ago (about when it started getting cold regularly here), I started getting a high idle when warmed up. It idles 2000rpm in P/N or 1000rpm in gear (you have to hold the brakes pretty firmly to keep it from creeping off when stopped at a light). It was a very sudden development, though there have been about 4 or 5 times it has done this for a stop or two over the years. It starts normally (no hard start at all) when cold and idles normally until you put it in gear the first time and drive off. Then, the next time you let it go to idle it is high. To make it more confusing, if I turn the air conditioner or defrost on and the A/C compressor clutch is called to engage, the idle drops down closer to normal (about 1200 rpm free idle or pretty much normal in gear), until the A/C clutch disengages and it will jump all the way back up to 2000rpm. Also, I can shut the engine off (not touching anything other than turning the key) and immediately restart and the idle is closer to normal (about 1200rpm free idle). I've looked a little for vacuum leaks (though not thoroughly), and checked the fuse for the OVP. Any ideas?

Is the ABS lamp ON??

I would look around first better for vacuum leaks. Don't forget to check the brake booster hose on the left side of the engine compartment - it is fairly large diameter, stiff, with a plastic check valve in the middle that can fracture with age. Also caused reduced brake effectiveness in ours.

Steve