I have a 1995 440 with B18U and have had idle problems, including seeing the idle speed go up to around 2000 rpm. My main problem has been stalling at idle with hot engine and this seems to be due to vaccuum leaks.

There are two black plastic pipes which come over the brake resevoir and join the back of the inlet assembly using short braid covered pipes. I have these were perished and I have replaced them. Things look OK, but it is early days yet. Note that one of these pipes has a small brass restrictor in it, so don't throw away!!.

Also, the temp gauge and ECU definately use separate senders. ECU is on the fron with a latching connector, temp gauge is around the back with a blade type.

I have found a Haynes manual which gives all the info for reading ECU fault codes and doing tests. Covers the 440 well.

I have a similar problem, but at this point haven't got to the bottom of it. So far have had injection system cleaned, tune up -everything but plug wires, which seem ok, have replaced crank (rpm) sensor, and the coil. Now have found that the temperature guage is dropping back to cold just before it gets to regular running temp (about 3:00 oclock on the 94 850 non turbo) and within a couple of minutes, the stalling, then over revving, up to 3 -3500rpms begins, sometimes ( like this morning)it stayed t about 3500 til I shut it down, other times it goes up and down, tries to stall ,etc. been driving me crazy for about a month. The temp guage, and the fact that I haven't seen the fan running at all, are leading me to having that stuff checked ie, the ECT sensor an associated wiring/ connections, and the fan. Also will probably replace the thermostat while its at the shop.

Not sure this is the answer but I and my mechanic are running out of ideas... let me know if you get anywhere and I'll do the same.