Hi, I have an '89 300CE wth 70K miles that continues to challenge the dealer and I with a hot start problem -- excessive cranking and rough running for several minutes . Cold starts and hot starts within about 5 min of shut-off are both OK. No other drivability problems, other than occasionally when idling at operating temp, hot start rough -run symptom reappears on acceleration.

The original suspicion was fuel pressure leakdown, but it doesn't seem to be that.

Any suggestions appreciated. Here's the facts:

- maintains fuel system pressure at 2.9 bar for 60 min, according to dealer

- recent new parts: OVP relay, fuel pump relay, fuel pressure accumulator, EHA, fuel pump check valves, distributor cap, rotor, and spark plugs. (The EHA, distrib cap, rotor and plugs were replaced for other reasons; the others, my failed attempts at solving suspected fuel delivery problem.)

- air flow sensor plate zero position OK in fuel distributor

- coolant temp sensor for EFI measures OK at 20C but has about twice the resistance (~ 434 ohm) at 85-90C compared to spec. Is this enough to be the culprit?

thanks in advance...DAN

I didn't notice seeing that you replaced the wires. This can be an issue.

OVP was the cause of my hot start problem, but coolant temp sensor caused an erratic idle problem I once had.

Also, a faulty wiring harness shorting at the EGR was a culprit for poor driving performance. This was replaced free, as a service bulletin indicated that there was a harness problem with some W124 models.

I also had the plug wires replaced, and found that the spark plugs were gapped too wide, so car missed during load conditions. Put in new plugs that were correctly gapped.

Also replaced fuel filter (which you didn't mention in your replacement parts list).

Check the fuse at the top of the OVP as well...it will still cause big problems if blown...

HOT START SOLVED!

Thanks for all the suggestions and posts.

The culprit to this hot start problem anyway was the fuel injection nozzles. When they were all replaced. all the drivability issues vanished.

This 124 is an '89 300 CE with only 70K miles, previously driven for most of its life by an older lady, who probably didn't know what full throttle was. Use it or loose it, is what the technician related to me.

Kudos goes to Brooklyn Motoren Werke in Brooklyn, Wisc for their efforts!