My 1991 300e 3.0 Lt gas, when i start it in the morning it fire up after two trys, but then rpms is only at 500 with a rough idle, then press the gas and it smooths out a little bit. Need to know how to test csv to see if it is getting power. Now my check engine light came on and my O2 sensor needs to be changed out hopefully that help with the rough idle?

That issue can be caused by several things on that engine:

-Idle control valve stuck/dirty/failed
-Idle control valve hoses being cracked
-Other hoses being cracked
-Cold start valve
-Failed OVP relay
-Deteriorated wiring harness to sensors/valve
-Multiple start attempts needed can also be a bad fuel accumulator by the pumps
-EHA valve could be bad
-Temp sensors could be getting bad contact or be bad
-O2 sensor could be bad
-Mixture adjustment could be out of spec due to wear/tear/age
-Idle return micro switch could be bad
-Spark plugs worn or dirty/fouled
-Wires going bad/old
-Distributor cap/rotor worn (they do not last as long on this engine as on other engines)
-Leaking fuel injectors causing it to be flooded from the last time it was turned off

I've gone through/replaced just about all of these things to get my 300E in solid shape. Once I did it hasn't had a single issue in years...fires up every morning no problem.

The M103 is awesome when running great but an obnoxious nightmare when not running right.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Thank you very much for this good info. this weekend i start on the list u gave me, but should use a test light on csv plug to see if it is getting power? And the ovp relay where is that located?

OVP relay is a small aluminum box behind the battery, they have a black or red top with a little door with us-style fuses under it.

Not sure about a test light on the csv plug, I have never tried that.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Thank for the reply back, need to know can i clean the idle control valve and do that, from what i understand is clean it with some carb. cleaner, just dont want to make mistake and put the in the wrong place. Now the ovp relay, fuse is good could the unit still be bad?

Yes the unit can still be bad if the fuse is good. If it has a black top then it is original/old. Red top is a newer one but they can still fail.

As for cleaning the valve, it works only part of the time, sometimes the unit just needs to be replaced. Feel free to spray carb cleaner all over the inside. I usually put my finger over one of the hose connections, fill halfway with cleaner, cover other end and shake it for a while, then drain/repeat. Wear gloves...

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

You been so helpfully thanks once again!!!!!! I just checked vac. lines but notice the wires going to sensors upper part of the engine are brittle and seen some of the connection to the prongs were not good. Maybe i should buy wiring manual for my car need to change that wire harness out. Have u ever done one yet ( wire harness )?

I have repaired/fixed up my harness a bit, but have not had to fully replace it. If I had to to do that I'd probably order a whole new one from the dealer and just re-install. Would take too much time to try to remake it all by hand...

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

sounds good ok maybe one day i will do just,thanks again for your help!!!!!

Oh one more qustion the idle control valve it has two hoses, been trying look them up and had no luck do you know the name them?

If you want them to last I would buy new ones from the MB dealer.

Part numbers are: 103 094 13 82 for the hose going into the air valve
103 094 04 82 for the hose leaving the air valve

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Ok thanks