1995 420e rough idling - PeachParts Mercedes-Benz Forum

mbzdriver · #1 12-01-2003, 04:08 PM

I need help.... I have a 420e with about 75000 miles. If the car is driven daily it has no problem, however if it is not driven for about 4 days after 15 minutes of running it develops a rough idle with loss of power (as if it were only firing a few pistons.) This condition persists for about 10 minutes then it goes away.
It is very confusing......
Thanks

Joseph_H · #2 12-01-2003, 05:24 PM

in my 95 E420 I had that cold start hesitations and rough idling problem whenever i left the car in the garage for 2-3days undriven and the problem went away after 5-10 minutes. The only difference is that my car exhibited this problem as soon as the engine runs and not 15 minutes later like you describe. Since then, I have done few things and I haven't seen this problem come back yet. Here are the things I did:

1) Replaced vacuum hoses. Those are the small L shape that you can buy for $1.30 each from the parts store. I replaced everyone i could get my hands at. a total of about 8 hoses. Including the ones to/from the fuel pressure regulator.

2) Replaced O2 sensor.

3) Replaced spark plugs

4) Tested and filled battery with distilled water.

Doing all the above gave the car nicer feel and better pickup when moving from a stand still. I am an average DIYer and did all the above myself and didn't take but a couple of hours. Some of the suggestions I received when I first posted my cold start problems were to check my fuel pressure regulator, Coolant temp sensor and the Battery as someone indicated that a weak battery may cause this cold start until it gets full charge and then the problem goes away. Good luck finding your source of problem.

mbzdriver · #3 12-01-2003, 05:35 PM

Thanks Joseph_H, I will try the vacum hoses and O2 sensor, I have already done the spark plugs.
Thanks again....

deanyel · #4 12-01-2003, 09:51 PM

I had symptoms more like JosephHs - leave it for a week and it would start up very rough. I believe it was stuck lifters - just one or two will screw things up royally. Recommendations I got were: oil additive, synthetic oil, and don't leave it for a week.