w124 expert needed (part 2!)

[gt-83]

Guys, i think i jumped the gun when i marked my earlier thread (w124 expert needed) solved!
ive spent hours on this car, and exhausted the net of info, your thoughts please

Originally the car (300ce 1992) got up to temperature then died instantly, with the help here, it was narrowed down to a bad throttle position switch / sensor
A new sensor fitted and AGES setting it up (0.7 volts at idle) i thought everything was fine, the car heated up past the 85 degrees that it had previously cut out at

Started the car today, assuming all was well, the car started instantly, heats up nicely past the point where it used to cut out, but after about 10 minutes it starts "surging" , from 700 to 400 revs, eventually stalling.
I tried it again with the air filter off so i could see..... when it started surging i unplugged the idle control valve and the revs return to normal

I tried another ICV that i have and exactly the same, oh and i have tried another OVP relay, as im sure it would be mentioned.

Here is what i think can be ruled out through swapping parts
KE unit (ecu)
throttle position switch
micro switch on linkage
coolant temperature sensor.....and gauge sensor, just for good measure
OVP relay
and today idle control valve
any ideas guys..........im running out of patience with this car

 

[hotrodder]

Not an expert but as a problem with the fuel EVAP system can cause idle hunting on the later m104... 47 Fuel system - M103
I haven't read through them and am assuming the layout is similar to my 320 in which case there'll be a small black box on the n/side inner wing with MOT written on the top. This controls admission of fuel vapours from the charcoal cannister into the engine and once the engine is upto temp should be able to feel it pulsing when the engine is idling.

 

[gt-83]

THANKS HOTTRODDER, i will take a look in the morning
what i dont understand is

with the EHA disconnected the car runs fine
with the TPS disconnected the car runs fine
with the ICV disconnected the car runs fine

the only thing i can see that links all these is the ecu, though i have tried another ecu that i know is good with the same problem

 

[Peterjj]

Have you cleaned and checked the throttle body ?

 

[grober]

If the car has been sat around for a while it may have accumulated some moisture in the body of the distributor. When the car first starts its fine then as the block heats up that moisture migrates up to the distributor cap and causes a misfire. Cure is to dry out the body and cap thoroughly with a hairdrier. Other possibility is a build up of a vacuum in the tank through a blocked evap filter- To check this try running with a loose filler cap.