hard start
 

now that I have heat going in this car (87 190E 2.3) will try to eliminate the hard start. car will on start with gas pedal depressed. it start once with out depressing the gas after the spark plugs were changed out (from autolite to bosch)

and to add it will start with no problem when cold but once it has been driven gas pedal must be depressed

hard starting
 

I've got the same problem with a 94 c220. The MB dealer has replaced the fuel filter, fuel pump, injectors, mass airflow sensor, coolant temp sensor, air filter, spark plugs, vac lines, gas cap, and who knows what else. All that's left is the intake air temp sensor, the engine control unit, and the entire wiring harness. They have had two or three different mechanics working on it, but the problem persists and if anything it is worse. If you have a good independent repair shop close that has all the latest in electronic engine analyizers it might pay to have them check it out. If you find your problem before I find mine let me know what the problem was. The entire ECU system is so complex you can what-if yourself into bankrupcy. I posted a cry for help on this forum, but so far I've only had a couple of replies. Good luck and have a merry holiday season. I've got my Christmas presents sitting in the driveway, even if it is hard to start above 40 degrees.

Have them check/replace the oxygen sensor - that was what was the culprit behind the former cold start difficulty with my 1992 300TE 4matic. That and a loose vaccum hose.

I think marcus318 and I have a similar problem. My c220 will start great if the temp is in the 30's or colder. After the car has been run, if you let it sit more than 15-30 minutes it won't start unless you depress the throttle. Then when it does start it jumps up to 2,000 rpm then tries to stall out (no gas) and then goes to 1,200 rpm and runs rough for about a minute and then smooths out and idles down to 700-750 rpm like it is supposed to. After getting it started it runs like new. I think it's not getting enough gas and trying to start too lean. The ECU is either faulty or not getting the proper input from the intake air temp sensor or the lead from the ignition switch, which richens the fuel mixture while cranking the engine over. My local MB dealer can't find any codes in the ECU and they say they've tested it and can't find the problem. It could also be a wiring harness problem with some of the wires or connectors making intermitent connections.

What's different between starting a car cold and starting it hot. When cold, the engine needs a rich mixture to run properly. When hot it needs to be lean. If a temperature sensor doesn't report that the engine is hot, too much fuel could be sent to the engine, creating a "flood" condition during a hot start. Pushing the pedal to the floor opens the throttle plate and helps to lean out the mixture. You had to do this in the old days with carburators when you accidentally flooded the engine. I'd look for trouble with temp sensors and the vacuum hose's and vacuum operated valves associated with them. Air temp, coolent temp, stuck cold start injector, stuck or plugged EGR valve, bad vacuum check valve, air pump. The clue is that it starts good cold. Most guys run into problems with hot starts and running.

Warm hardstart?

Fuel pump check valve or fuel accumulator.

If either of these items fail, you will experience a hardstart when warm - similar to vapor lock.:)

Do a search on these 2 items.

Cheers.

hard starting finally cured
 

It took about 3 months and a lot of parts (maybe some were bad, maybe some were good, and maybe some were in between), but the main problem with my c220 was in the wiring. After replacing the entire engine wiring harness and both the primary and secondary wiring on the coils my baby benz starts and runs like new.