E30 Zone

Hi guys, I'm new to the site. I was guided her by 1 of the guy from bimmerfest. Said you guys know M10 engines. Well I have an 84 318i coupe, 5spd manual w/m10. I have a couple of problems. 1) My temp gauge or odometer isn't working
2) It idles high, about 1800-2200rpm.
I cleaned and checked the ICV it works. I also replaced all hoses except 1. My mechanic friend thinks problems could be LINKED. He thought it could be thermo time switch.
I saw in the bently manual something about it affecting temp gauge and the cars idle speed. The previous owner did swap speedos though( loose wire/ bad speedo??) Sooo maybe 2 separate prob.???? I'm saving back for the thermo time switch but its pricey. Is there a better place to start??? Please help. Ohh the speedo is off by 5mph too.(Not sure if it matters)

Your odometer doesn't work but the speedo. does?
Your speedo. is designed to be 'out', it should read faster than you are going.

if the speedo works and no odometer then my money is on the plastic cogs have worn out ot become brittle and broken, this is common in hot countries but not so in UK - assuming thats where you are.

Also given the amount of issues with the dash are you sure its the correct dash in there..ie not one for a 6 cyl? have you checked the engine speed with something independant (ie a tachometer that runs from the HT lead?..your mechanic friend should have one of these).

as for the temp affecting idel this is correct, but there are two seperate sesnors, one (the brown temp sensor) is only working the guage, the other (the blue temp sensor) is what tels your ECU the engine temp and thus it adjusts fuel/air mix accordingly, it would not in my opinion casue the RPM to be at 1800-2000, where as normal is about 800.

The OP is in the USA...I told him on Bimmerfest to check the plastic cogs and the brown sensor and the TPS.

I do not know the M10 too well so advised him to try this forum for some more advice!

OK if in the states then 100% the cogs, easy to change but you need to get the correct ones (Miles or KM) but to be honest its just as easy to swap for a known good speedo. but look on US Ebay and they sell the cog sets for about 50 USD.

M10's work like almost all engines (except a different engine mangement system being the older Jetronic system) in that they take different signals such as engine temp, engine load, Throttle position and adjust the fuel map accordigly.

Jetronic Idle is controled by the idle air control valve which sends a signal to the idle control unit (under the dash board), a classic test on the older cars is to unplug the wiring harness from the ICV, if it is working then the RPM jumps upto 2000 rpm...this is what the OP's car is doing so my guess is the ICV is not working, or the wiring between ICV and idle control module, or the idle control module. there are tests for it such as the resistance between the two pins of the ICV should be 9-10 ohms, and if you connect an ammeter into the circuit when running AT Correct Temp, the current from the ICV to the control unit should be about 450-470mA for a manual and 460-480mA for an auto. you can adjust the resistance (and thus the current output) as the ICV had a screw, but i would not suggest you play with this too much as if is at 2000 RPM then there is more than an adjsutment issue