'93 m103 starts fine cold, hesitates upon warmup
 

I have a '93 190E 2.6 that starts, idles, and runs fine when dead cold. Upon reaching operating temp, it idles a little rough and stumbles/hesitates when applying throttle from a stop. This car is from GA and never exhibited this problem until I brought it to DC where it actually gets cold in the winter. I would describe the symptoms as similar to those one would experience if one tried riding a motorcycle with the choke open. Does anybody out there have a clue what's going on here?

Check your coolant temp sensors for starters. Also might wanna check air intake temp sensor. There are plenty of posts here on how to do that, try a search.


-tp

Vac leaks?

Check the rotor and distributor cap.
 

This is fairly easy to do except for that one hex bolt under the distributor. I think it's a 5mm. I had a problem just as you describe that quickly turned into a stalling issue once the engine got up to temp....would start again after a cool down period. The last item in my chosen chain of tests and inspections was the distributor cap and rotor as they were fairly new. The rotor and cap contacts were nearly gone due to corrosion. I'm guessing the o-ring was compromised allowing moisture in but it looked good to me. $70 to our gracious sponsor and all has been well for quite some time.

Y'know, one time I had a similar problem with my 103. Turned out to be that funky breather hose behind the big one. The one with two 45 degree bends. It had cracks all along the underside that were not visible. Once the car warmed up, the cracks opened up causing a huge vac leak.

Easy fix, and worth checking regardless.


-tp

EHA Valve?
 

Just to throw another possibility out there: My '88 260 would hesitate badly in cold weather. Start up was fine, but as the coolant temp went up and the engine controls went to closed loop, hesitation would set in.

I checked just about everthing before finding that the EHC was the culprit. The clue was a slight gas smell under the hood after driving caused by a crack in the EHC. The leak was not big enough to see any fuel, but you could smell it. I would definitely suspect the EHC if you have a fuel smell around the EHC.

Bad news is that the part is expensive. I found a new Bosch one on EBAY that was just fine and not too pricey.