M103 slightly high idle
 

Hi everyone!

I'm having a slightly high idle issue on my 103. When fully warmed up (80c), it idles at about 1000 rpm in park and about 800 rpm in gear. Also, it no longer does the 1400-ish rpm fast idle when warming up from cold start. It just stays the same.
What I did last weekend was: replaced fuel injectors and seals, intake boot under airflow meter, both idle hoses including the nipple that goes to the intake boot, cleaned IACV out with carb cleaner, replaced ALL underhood vacuum rubber connections and hard lines (in-cabin lines and connectors were done over the summer), replaced throttle micro-switch on linkage (old one was missing part of its little contact wheel), and lubed throttle linkage. All of this was done with genuine mb parts. I did all of this for old age maintenance, since this stuff was all original.
Thing #1: I did not have this issue BEFORE doing all this stuff, so I must have either screwed something up, or I need to make adjustments to compensate for new stuff.
Thing #2 (more important): when I disconnect the electrical plug for the IACV, the idle immediately drops to normal 800 rpm in park, 600 in gear. Plug it back in and goes right back up.

Any ideas? I have not tested anything electrically.
-Chris

I should also note that I recently had the 2-pole green temp sensor at the back of the head disconnected when I did my head gasket a couple months ago. I'm not sure if i got those two connectors back on the same poles, I dont know if it matters, they look identical.

No problem with the tem sensor no special way they go on .Left right or right left .

Stormy the temperature sensor is resistor only and should read 38 ohms to ground across both poles .Now this sensor sends a message to the ecu if faulty it will send wrong information .Do the check on it if you can .

I'll check it out thanks!

Storm have you a workshop manual ? But what is your car ,is it a W124 ?.

Yes and yes. I use both the 124-zone website and 124 performance website for the manuals.
Car is 124, 1987 300e 103 motor

so stupid question: whats the correct way to hook up the leads of my multimeter to the sensor?

Ok so I tried testing the sensor with the engine at operating temperature and got 28. I had the negative lead of my dmm grounded and I probed each prong, they were the same. Then I tried testing it by putting the positive lead of the dmm in one pole, and the negative lead in the other pole and got something like .1 or not even a reading. I had my dmm set to 200k (free harbor freight dmm). Im good with testing for voltages, but a bit of a novice when it comes to testing resistance. Any advice would be appreciated!
-Chris

Throttle microswitch. If its not full closed idle will be high. double check it and make sure the small pin gets depressed.

Storm set dvm to 20k do on a hot engine .You put the red lead of the dvm to one pole of the sensor ,and the black lead of dvm to earth [engine]. Same with the other pole ,red to pole black to earth .Check the reading .on both hot and cold engine .Let us know ,

Ok, will do optimus thanks! Microswitch works correctly, i just put a brand new one in as the old one was missing part of its contact wheel and not making contact at all. Didnt really seem to make a difference- if you press it with the engine off of idle nothing happens.

-Chris

Ok so the sensor read 5.55 ohm resistance when cold (grounded straight to battery), now letting engine warm up fully...

Aand.. with engine fully warm at just above 80c it read 0.00 giving a little flicker now and then to 0.01. So providing my multimeter is reasonably accurate, it is safe to say this sensor is no good if its supposed to be at .38? Sensor looks terrible anyways...

Got the new sensor...idles much better now, the old sensor was cracked on top!