300e Stalls when cold
 

For the past 2 months poor idle when cold.

Once past idle runs smooth with great acceleration.

Today, idle was worse than before. After driving four miles I stopped at a red light and the car just barley restated. Drive at 55 mph for one mile stopped at another red light and the car would not restart.

Two hours later the car did restart with poor idle and did drive for two miles to home.

What do you think?

Notes: no vacuum leaks, plugs, wires, cap, rotor three months old and have been rechecked. I am a retired auto teck with only limited experience on MB.
:confused:

hmmmm
 

You might wanna check that notrious overload protection relay that everybody is griping about on the forums. It should be back behind the battery hanging off the side of your engine control computer, it's the one with the flip top and ATO style fuse under the clear flip cover. You also might wanna pull your idle control valve, clean it out with some carb cleaner and make sure it's opening and closing properly, these do have a tendancy to either stick or plain burn out after a 100k+ miles on jetronic systems. As far as I can tell, MBZ ignition systems of this era are extremely sensitive to plug gap as well and it's pretty short, like .032 or somehting along those lines.

Stalling while cold only is probably a vacuum lean since the computer isn't doing anything but running a fixed mixture until the heater on the oxygen senor warms up. If the problem starts up a minute or so after starting, check the oxygen sensor.

Also check the function of the idle swtich. If not closing when at idle, the mixture will be too lean.

As for the relays, a bad fuel pump relay will do this, will the added bonus of stalling intermittantly all the time. However, you need to check the current draw on the fuel pumps as well (there are two) -- excess current draw will fry a new relay and leaver you right were you are again.

If the tach jumps around and the ABS warning light flickers or comes on when the engine is idling rough and slow, its the OverVoltate Protection relay (OVP). These are notorious for going intermittant. Easy check is to shake it -- if it rattles, it's bad (ditto for the FP relay).

If these don't fix the problem let us know -- you may have other problems with the fuel system.

Very bad valve guide wear will also cause serious idle problems, so will bad fuel injectors (you will burn enormous quantities of oil if the guides are bad).

Peter

Back on the Road
 

The Overload relay was replaced as you suggested. Still the car did not run so I checked the cap and rotor finding the rest of the problem. After these parts were replace the car runs great hot or cold.

Thank you,

Max

I'm confused. :confused:
What did you do to correct the problem? You said the wires, cap, and rotor were replaced 3 months ago and rechecked.

Peter

Bad Relay, Rotor, and Cap
 

Dear Peter:

Thank you for your concern. Apparently there were two problems not one. The overload relay corrected the poor running when the engine was cold and it may have contributed to the no start problem. The cap and rotor which were replaced about three months ago somehow were defective. The rotor after careful inspection had been arcing and the cap due to this problem was disfigured. After all three parts were replaced the car immediately started and runs properly.

Respectfully,

Max

Max,
Thanks for clearing that up. I've got the polly grip on it now. Sometimes two problems at once can really mess you up in the diagnoses dept, because the symptoms don't point in the direction of any one component.

The reason the OVP was causing poor cold performance is, because the computer was out of the loop and couldn't send a rich mixture to the engine during warm up mode. You were experiencing the same problems as a carburetor vehicle without a choke. Glad you got it figured out

Peter