1991 300 SL stalling/restarting

[Shaggydog199]

My 1991 300 SL (52000 miles)will periodically stall when comming to a stop. Both the idle control valve and oxygen sensor have been replaced and the fuel mixture was made richer. It still does it! Only happens periodocally and usually when stopping after acceleration. The real problem is it won't retart for about three minutes. Then things seem fine. If I keep the RPM's up by applying slight pressure to the gas pedal while stopping it will not stall. I'd like to give my crack mechanic some advise so he doesn't continue to guess!

Any ideas on the cause and the reason why it will not start for awhile. Very embarassing to be sitting at a busy intersection in a beautifull Benz with the emergency blinkers on!

jim

my 91 300sl with 140k has an intermitent sputter and sometimes stalls. although it will always start right up. i took it to a mechanic with a good reputation and he cleaned the fuel injectors and it has almost fixed the problem. ive only had the car back for a few days and it has not sputtered yet. fingers crossed. he explained to me the problem but i dont quite understand. might be a place to look

[Gilly]

That complaint sounds EXACTLY like a bad overvoltage protection relay, exactly the complaint MB has written up in the diagnostic directory.
Gilly

[Shaggydog199]

Gilly,
Thanks! That was replaced as well. The stall happened once since the repairs. Is there a 'settling in' period? Still took three minutes to restart.

Anyway, when comming to a stop, the idle goes to 1000 RPM's, then drops to 600-700. Bounces a little. I fear it is going to stall again so lightly apply some fuel to keep it at 1000. I suppose I need to stop that to see if it stalls again.

This all sound normal to you?

Jim

[pmizell]

Have you checked your voltage regulator attached to the underside of your alternator?

With only 52k miles, it's unlikely the regulator is worn, but you never know.

[Gilly]

Jim:
No, the "settling in" thing doesn't make sense, either it's fixed or it isn't.
On this vintage 104 engine, I think maybe the best course of action may be to hang a fuel pressure gauge on it and try to get it to act up, that way at least you'll be pretty sure it isn't a fuel related problem. I can't remember on your car if it has a fuel pump relay or a slightly different type of relay called an MAS relay, I tend to think it's a MAS relay. If this is intermittently failing it could be causing the fuel pumps to stop working.
By the description you gave I would have sworn it had to be the OVP relay, maybe the MAS relay could be failing in a similar manner.
Another thing a tech could do is if it were in a failed state you could remove the MAS relay and install a jumper wire to see if the pumps then run and the car starts.

Gilly