190D 2.2 Low Idle and No Tach - PeachParts Mercedes-Benz Forum

DieselPaul · #1 03-01-2014, 09:50 AM

For those who have read my other threads... it has happened again, but to a different car.

Just bought this 1985 190D 2.2, my dad has put 1300 miles on it in a month. We needed a spare car for the winter while other cars were put away or broken so I went out and bought this car. 280k runs and drivers really well.

Car was idling great and the tach was working. My dad brought it up from Cincinnati to Columbus for brunch and we decided to throw some fuel filters on it because I had no service records for the car and the prefilter was black. Took the air cleaner off to get to the prefilter and replace any seeping lines. Put back together, primed the spin on with ATF. Started right up, but was idling low and had no tach. Drove it around the block, no change.

He had to drive it back to Cincinnati, and put 500 miles on it with the low idle and it has not fixed itself, nor gotten worse.

He came up this weekend and I tried to fix it:

Cleaned all the connections I thought were related to the ELR.

Tried 5 OVP relays

Tried an unknown ELR relay (just bought another spare on it eBay I'll try next time I see the car)

Tried the crank sensor out of my wagon

Fuse 10 (tach and emissions fuse) is good, put in a brass one for good measure. Have power on both sides of the fuse.

Opened up all the connectors for the OVP and ELR and tightened the metal part of the connectors so they would not be loose connections.

Pull the airbox back off and looked for any pinched or squeezed wires, did not see any

Cleaned the battery terminals, the ring terminals from the alternator, and both main grounds.

It has to be something I damaged when I was working on the car. I took the airbox off, and I also pulled the cowl off to get to the heater control valve to pull vacuum on it (heat is stuck on)

So what could have damaged or unplugged?

Which connection on the injection pump itself is related to the idle control?

I've read people talking about "tone-ing out" wires to test to make sure a wire in the harness has not broken, what is a good way to go about that?

I am thinking maybe the 30 year old harness exposed to 280k miles of heat is brittle and maybe I broke a wire or something that is hidden in the harness.

I'm stumped, but mostly annoyed because I know its something I broke haha.

Any thoughts appreciated. Thanks!