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89 260e M103 engine 6-cyl.

Here is the situation:

Engine cold: starts fine, idles around 1,000 rpm and settles around 700-800 once warmed up.


Engine warm: starts, stalls right away unless you hold the gas pedal down a bit or try to start it about 3-10 times without holding gas pedal down.


Engine warm but bypass coolant temp sensor (for ECU) with a 10k ohm resistor (this makes the ECU think the engine is cold, -10 degree C).

with the resistor, engine starts fine on first try without gas pedal depressed and idles around 1250 to 1500 rpm (since ECU thinks engine is real cold).

Even with cold start valve DISCONNECTED, the engine starts fine on first try with 10k ohm resistor bypassing the coolant temp sensor.

With all the 10k ohm resistor tests, the engine is actually warm 80 degree C

Anyone have any feedback on a solution/diagnosis?
 

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1987 300TD W124 sedan
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Actually, I think those links will help you.

Here's another one: http://www.w124-zone.com/downloads/MB CD/W124/w124CD1/Program/Engine/103/Prog_Repairs/comb1.pdf#page=23

Not sure if you're fuel injected or not, but it is a classic case of flooding with a carbureted engine, dirty cap-n-rotor, bad coil(overheats on initial start up won't restart until it cools-too hot).

I also saw in one of the troubleshooting links cbc atl gave that the O2 sensor wire can ride and short out on the drive shaft... I fix boats and still can't get used to them calling it a propeller shaft...The short can cause a hard start.

If it were me, I start simple first; cap-n-rotor, warmth test on coil- feel it with your hand but don't burn yourself, yes, they can and is why they leak oil when they go bad-overheated seams in coil. If you can touch the coil(s) and it's just warm, usually ok. Check specs to see what coil resistance is too. Then crawl under the car to check O2 sensor.

If you're carbureted, you may have a float problem and why it's flooded on restart. Easy way to restart a flooded carb is to hold pedal to wide open throttle until it starts(more air than fuel) then release pedal immediately when it fires off. Might take twice to start. Keep air cleaner on when doing this in case of backfire, you don't want to shoot raw flaming gasoline into your hood insulation. Even throttle bodies can flood, or starve if dirty.

If fuel injected, you probably have an electric fuel pump(lift), they too can overheat and go bad. Pressure test this and ohm's check per spec.

Those are the simple items on gassers, kind of archaic, but most common throughout the engine world.

It never ceases to amaze customers the difference a cap-n-rotor makes.
 

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