CAR: 1987 300e w124 - 184,400 miles
PROBLEM: Engine starts, but won't idle.
LOCATION: Austin, TX


I can start the car and as long as I keep pumping the accelerator or keep the rev's high (3000-5000rpm's) the engine will run and it will run forever, but as soon as I let up a bit or let it drop to 1000 rpm or less, it will continue to drop to 0 and the engine dies. Not enough time to get the transmission into [D] and actually try driving it.

The car is too old to speak codes to me, I'm told.

I've done all the affordable stuff I know of:

Replaced sparkplugs
Checked Spark
Compression test
Starter fluid test
Sound check for fuel pump
Disconnected flywheel position sensor

Results:
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Spark check: My friend held one of the sparkplugs to the block and got a good shock: good spark but bad boot, but would this stop the car from running?

Compression test: good, range 159psi - 178psi

Starter fluid: Had someone spray starter fluid, while I started the car. Engine ran as long as both the fluid was being sprayed and the accelerator pedal was being pushed down.

Fuel Pump: Heard the 1 second buzz under the car that someone said signifies the fuel pump is working, supposedly.

Flywheel position sensor: I unplugged the sensor from the EZL, the engine didn't even want to turn over until I put it back. Does this eliminate it as a possibility?

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If it means anything, the car stopped working properly without any previous symptoms and without warning. It went kaput when I tried starting it one night, not while driving. I also thought I heard a small single thud coming from under the hood at the moment the problem started.

Thanks for any help,
david

I know you got a good spark but check the cap and rotor anyway. 103s are very fussy about their rotors and the rotor housing oil seal has been known to leak fouling the mechanism.

Sounds like you need a fuel system pressure test to check the system components and fuel return flow. There was a 300 SEL owner recently who had a clogged fuel return line.

I believe your ar has an Idle Control Valve. On my 4 cyl it's located between 3 & 4 air runner wrapped in a rubber sleeve. They tend to get sticky from sucking up the blowby from the cylinder head.

To test, unplug, ground on one terminal, then tap the other terminal to + of the battery. You should hear a click when you do this. If you don't, switch the wires ( ground the other term and connect the other to + ). If you still don't hear the click you now have to check if the valve parts can rotate open and close. Shouldn't take much force to do this with a screw driver and take care not to gouge it.

If it's stuck blast it with carb cleaner, plug-side up, valve pointing down. Some guys soak the valve side overnight. Test and lightly lubricate before installing. If it still doesn't click...2 things: either the valve is busted or there's not power going into it (OVP I think).

Check cap and rotor, then look for a hose off the idle control valve (remove air filter housing). Likely the rotor slipped, it backfired, and blew the idle control valve hose out of the rubber boot between air flow meter housing and throttle valve.

There is a part on the end of the crankshaft known as the rotor carrier. These break and cause the rotor to slip and the spark to be delivered to the wrong plug, or in your case, possible far enough off that the spark cannot jump to the correct pin except at full advance.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!