W210/E320 hesitation & starting problems
 

My wife's '98 E320 is having intermittent problems starting and brief hesitation when accelerating.

I bought the car used a couple of months ago with 62K mi. It was missing the service records, but appears to have been maintained. Regardless, I've been doing all the Schedule B and AP service myself so I have a good baseline.

About a month ago the check engine light came on, but the car drove fine. A shop said it indicated "fuel trim" and reset it. They said to bring it in if it happens again.

Yesterday, my wife had problems starting it. It would crank, but not start. After repeated tries, it started right up like normal. This happened twice in one day.

I haven't been able to duplicate the starting problem yet, but did notice some hesitation once while accelerating.

I'm guessing I have a fuel delivery problem, but I haven't found a source for service manuals for a W210, so I'm not clear how to proceed. I replaced the fuel filter a few weeks ago. Can anyone tell me the procedure for replacing the fuel pump and fuel sending unit? If they are easy enough, I'll try them first before I take it to a shop.

air flow meter


Joe

Joe, thanks for the reply. Are you suggesting the Mass Air Sensor (MAS) based on the check engine code, the symptoms, or both? The reason I ask is that the car drove fine when I got the "Fuel Trim" code, and now that it is driving bad, I get no check engine warnings.

I would also like to point out that it idles fine, no stalling. The times that it wouldn't start were after my wife was doing quick errands, so the engine was hot. The hesitation happened when the engine was cold.

Does this still sound like MAS?

i'd bring it to the dealer for proper diagnostic.

Check engine tripped again... MAS code.

I finally encountered the starting problem. Engine just cranked until I tapped the accelerator pedal.

Fuel trim code, MAS code, internittent starting and hesitation problems, does this still sound like Mass Air Sensor?

Update: Another check engine code: fuel trim (P1070, P1073). My intermittent starting problem is happening most of the time now, and tapping the accelerator pedal to start it only worked once.

The computer is pointing to air flow meter (Mass Air Sensor), but I haven't seen any of the postings relating to MAS indicate starting problems.

Have anyone seen failed mass air sensors cause starting problems?

Thanks!

Update:

I replaced the MAS, and have not had a check engine light since. I'm still having problems with the engine not starting. I think I've had two unrelated problems, and replacing the MAS fixed one of them. I'm going to post a new thread to clearly address my starting problem.

Thanks to all for the advice.

Update:

Problems solved. I indeed had two unrelated problems. The stalling and starting problem was caused by a bad knock sensor. The hesitation and check engine lights (codes P1070, P1073) were caused by a bad mass air sensor.

Based on this experience I'm considering the purchase of a good OBDII scanner.

OBDII purchase
 

If and when you get an OBDII meter, could you let us know what you found? There seem to be a number of the market, but have to watch that it decodes various extensions particular to one manufacturer. Thanks!