Luke-Warm Start Question (M103)
 

I have had a relatively steady luke-warm start stumble in my '91 300E. I thought it was the cold start valve leaking down, but my research suggests that these almost never fail. It usually only happens the car is not entirely cold (needle registers something on temp gauge) but not when the car is restarted at or near operating temp (though it does occasionally happen when the car is totally cold). She got a new EHA a couple of years ago, and I have checked duty cycle (back when it was warmer out) and it was w/in spec.
I have read that the resistor in the coolant temp sensor can start to disintegrate sooner or later, creating a problem like this. Think this is the culprit?
I can live w/ the problem, I just hate the sound of the poor girl stumbling and coughing for 15 sec and fear what it might be doing to the engine, running lean like that.
We fixed a similar problem (well, almost entirely fixed) in our '91 300TE w/ duty cycle adj.
Any opinions?
Thanks!
-Matt-

It sounds more like an ignition problem. Specifically a plugwire end.

Steve,
Really? Plugs and wires (Behr's) (cap and rotor too) are new as of a few months ago when I gave her a full head job and condition existed unchanged before and after. Could it be the coil? It sounds like she is running lean, and if I give her a little pedal, she'll chug hard up over 1k rpms and then smooth out and idle clean when I let off. Just rough and ugly for about 15 sec when fairly cool and then fine. :confused:
-M-

Could I be looking at something air related (never considered this...may be nuts) like a MAS or the IAC?

You didn't use Bosch plats did you?

I doubt it is the coil. With this new info, my new best GUESS is that it is something else.

I have the exact same issue, and read where a small set screw in the back of the EHA module can be adjusted with a small clockwise 1/4 turn, w/ an allen key.

I thought I'd try it but have no knowledge / confidence that I could even find the EHA to begin with!...anyone know how to describe to a non-techie how to find / remove the EHA on a 90 300E?

Steve,
Car had the Bosch four prong plats in it and changed them out to Bosch single prong plats, so I could set the gap (and because they were all I could get in my area other than Autolite and I haven't had good experience w/ them). Should I order some Bosch Coppers?
Any advice on the EHA adj?
I have read a few posts here, but am unsure of the safety/effectivness of such on operation, it is an very expensive little black box.

Ottobun,
The EHA is located on the back of the fuel dist. Dig around in your manual if you want to get it off.

Thanks!
-Matt-

Yup. Those engines hate plats. Check your manual. Coppers are the only specified plugs. MB does not recommend plats, and with good reason. Might not solve the problem, but will preclude another one cropping up.

The Bosch copper plugs to use are either H9DC or H9DCO.

The H9DCO has a slightly wider side electrode. Some believe it produces a better spark. I've run both and cannot attest to that claim. Interestingly enough, the last set I pulled was H9DC and I got better gas mileage on that set than any set of H9DCO ever used.

Either plug will do well for you. As mentioned above, the plats are supposedly bad news in 103 motors. It isn't so much the motor, but the CIS FI system(according to info posted @ this site).