I'm posting this because I've read through thread after thread of the same symptoms, some of which have been cured by OVP relay, CPS, distributor rotor, etc. usually after throwing a myriad of parts at the problem.

Working on a buddies '92 300E 334,000 miles. Replaced his fuel distributor a couple years ago (because the Benz dealer got it started with a new coil, but didn't fix the intermittant stalling problem) and it ran fine for a good year or more. As far as I know it was running fine when parked. Car sat unused for a year or more before I was asked to get it running again. Put about 5 gallons of fresh fuel in a nearly empty tank with Techron fuel cleaner. Changed the oil and filter due to dirt and fuel dilution. Initially had alot of white smoke, but this has cleared up. Now exhaust is normal if slightly rich at idle, sooty when goosing the throttle.

Car starts fine when cold, idles reasonably well until the operating temp nears 80*C at which point the idle will drop to 500 rpm or so and the car will eventually stall and not restart. Haven't had the opportunity to wait around to see how long it has to cool before restarting, but always restarts the next day or whatever.

New spark plugs (Champion Copper Plus, the old Bosch Super had same symptoms) which show minor carbon fouling, fairly new wires.

New oxygen sensor.

Distributor cap looks like new. Cap, rotor and coil all replaced at just over 300,000 miles, prior to the fuel distributor.

CPS reading was around 800 ohms cold and 880 ohms after stalling if I remember correctly.

Temp sensor readings seemed to follow the table fairly well going by the guage on the dash up to 80*C and readings were within about 0.020 ohms of one another but not identical.

OVP seems ok ... no blown fuse, no abs or eng lights other than low windshield cleaner for obvious reasons.

Fuel pump seems to be operating correctly.

Unplugged the cold start injector after last startup, same result. Runs fine until warm.

All vacuum lines and hoses look to be in real good shape.

Transmission modulator not leaking, no fluid in line.

Suggestions as to what to try next?

This car has three (I think) temp sensors on top of the head along side of the valve cover. A sensor, a sender and a switch I believe. The one farthest forward with two prongs is a temp switch for the auxiliary fan only (I think). The middle one with only one prong is a temp sender for the gauge and the one closest to the firewall, with 4 prongs, is a temp sensor for the fuel injection only. I don't know which one you tested but the latter might cause such symptoms if bad. You can find the testing specs in the FSM or probably here in the forum if you search.

There were a few different set-ups so I'm not entirely sure of all this info as I didn't research it prior to posting. I think they changed to a three prong temp switch which doubled as a sender and eliminated the one prong sender ??, Anyway, not sure, but I'm pretty certain about the existence/location/purpose of the 4-prong sensor.

Yeah, long-gone, the four prong is the one I tested. It seems to be functioning properly assuming the temp guage is fairly accurate. Could be a little off, but I think it's close enough to allow the car to run.

I'm thinking my next test should be to check the resistance in the distributor rotor before starting and after stalling to see if it is bad.

the rotor resistance and the coil if winding is effected by high temp.
or substitute with another one
mak

Yeah the rotor resistance was high, anywhere from 130Kohm cold to 30 Kohm hot. OVP relay was corroded inside, and didn't throw the ABS light due to that circuit being closed. New temp sensor has the same variance as the old, so the readings must not have to be identical as stated in the manual. Didn't swap that out.

So here's the deal: new oxygen sensor, good bosch non-resistor plugs, new rotor, distributor cap in great shape, new thermostat, vacuum lines like new. CPS tests 800 ohms cold, 880 ohms hot. Idle valve seems to work fine. Plugs are carboned up but not wet when stalled.

Car starts fine cold, idles/runs rough, sooty rich exhaust, stalls when operating temp reached unless rpms are kept up. There is still fuel flow and spark after stalling.

Just an update for anyone interested: I was able to get the car to run fairly well with a lambda adjustment, but there was still hesitation and intermitant hard hot starts. Still too rich, apparently an internal leak and perhaps problems with the EHA valve. I bought a used fuel distributor/air meter assembly and made the swap this afternoon. At first I was concerned that there was still a problem running rich, some white smoke on initial start-up and idle. I think the computer was able to make the necessary adjustments and any excess fuel worked it's way through. As of this evening, so far so good.

I am having the same hot start issue and have pretty much narrowed it down by reading many threads that it is more than likely the fuel accumulator (located by the fuel pump). I just put new plugs (Bosch +2 Platinums) and a new Air temp Sensor (Bosch) in and it drastically improved my idle in gear. However, the hot start is still an issue and I have to crank if no start on first turn. What I have started doing now is stepping on the gas and turning the key and it starts right up but not like it should. It makes sense that if the accumluator loses pressure after sitting a while that the necessary immediate pressure and fuel is not there to start car. A few guys with my same car said that once they fixed that, idle was restored, starting was instant and car even had more pep when going.

sptt, consider replacing the fuel pump check valve.

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Fred Hoelzle

Ferdman...where is the check valve located and what does it look like? I take it that it maintains fuel pressure or something?

All these hot breakdown threads that are unfinished.

Does anyone ever say "I fixed my car, it was the ......."?????

Make sure that you've used a code reader to find out what codes the car is throwing. While trying to clear codes on my '90 300e, two of the codes pointed to a bad coolant temp sensor (it's the black headed one with the four prongs). I initially thought that the plug that attaches to it might have been attached wrong so I rotated the plug 90 degrees. While test driving it, it wouldn't start when warm. If the sensor is defective, it seems to confuse the engine management controller and shuts the car down.... or so it seems.

The proper way to test this sensor is to test the resistance of two poles diagonally across from each other(like an X) to make sure that the values are the same. This sensor actually has two thermistors that have poles opposite each other. In this way it doesn't matter which way the plug is attached. This sensor seems to be critical feedback for the engine management system. The readings bounce around so make sure you test it a couple of times to be sure. On my bad one, there was one pole that was bad so the readings wouldn't pair up.

By the way, to install it you'll have to unbolt the valve cover and tilt it up by a couple of inches in order to have enough clearance for the 7/8's deep socket you'll need to remove and install.

Hope it helps.

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03 CLK430 Cabrio 211K Pweter Silver/ Oyster Leather
90 300SEL 214k Pearl Black/ Alto Grey/Black Leather

Prior: 85 190E, 88 300TE, 89 300TE, 90 300E 2.6, 90 300TE, 92 300E 2.6, 91 and 93 300SL, 87 Ferrari Mondial Cabrio

My last post said I replaced the fuel distributer due to an internal leak, which seemed to clear up the problem. It's been over five years now, so if I remember correctly, he drove it for a couple years with no problems. The car is long gone now.