I discovered something very interesting this past weekend after i spent $40
to have my 850 turbo diagnosed to have a bad Idle Air Control valve.
After spending an additional $130 for a new, the problem still existed with
Black Smoke, Up and Down Uncontrollable Idle, Flooding, hard starting etc..
I could start the car and drive it but it would jump and sputter and
sometimes cut off as if the fuel pump was intermittently working and when it
cut off, somteimes it would start right back up and sometimes it took 30
minutes to start. I was pissed.

So while in the driveway scratching my head, I decided to try and fix
another problem I was having with the Temperature gauge. It has always been
somwhat lazy in the fact that it would never get over about 1/8 of dial.
That lead me to think that maybe the thermostat is getting weak.
Eventually the Gauge just stop registering at all. So I thought, Well could
it be a bad gauge or sender unit. I always try to tackle the easiest option
1st which was check the sensor / sending unit.

This is where it gets interesting......

Unplugged the Temp Sending unit (held by a clip just above the alternator)
and measured the resistance. Got 33 megaohms. This seemed a bit high to me.
I was thinking it should be more in the Kilo-ohm range. So I plugged it back
up and started the car.

With the car idling (Sporatically as mentioned earlier) I unplugged the
sender unit and the engine smoothed out. I mean REALLY smooth Idle.
Plugged the sensor up again and the Idle went high as Hell! almost redlined!
unplugged the sensor and the engine dropeed back down to normal RPM, about
800. Hmmmmm.... So i replaced the sensor and all my Idling, Black Smoke, cut
offs, stalls, bitching and moaning went away! No more problems (knock on
wood)

Temp sensor....If you are having stalling problems try checking or changing
your water temperature sending unit.
Just my 2 cents
 

Horace D. Cates
 Field Service Tech (FST)
 300 Blake Street
 Raleigh, NC 27601
 919.833.2549 ext. 106 voice
 919.754.7032 mobile
 
 

              Thanks for this great troubleshooting tip, Horace!