1994 Yukon 350 TBI Loping / Stalling

[rsulliva]

I have a 1994 GMC Yukon 350 TBI 4WD that has a significant lope to the point of stalling, especially when in gear. When in park it will lope between 800 to 1000 rpms and when in gear sitting still will lope between 200 and 700 rpms and every so often, stall out. You can feel an intermittant stumble when actually driving although tach doesn't show it then. The stall will also occur sometimes when coming to a stop. The motor has plenty of power. Changed almost all sensors/components - see below for list of replaced items. I can temporarily fix the issue if I unplug the Coolant Temp Sensor the truck will stumble really hard several times and if it doesn't stall, it will smooth out completely 800 RPM for about 1 minute then starts to stumble again. Putting the vehicle back into park, plugging the CTS back in then putting the vehicle back into gear for about a minute then unplugging the CTS again will once again will repeat the temporary fix most of the time. Plugging the CTS back in once the lope has started has no effect. I have checked the voltage going to the CTS and it remains a steady 5V. I have tried 3 CTS's with the same results. Also about one in every 20 trips the vehicle will show no signs of any lope or stumble or very little. Could this be a PROM issue?

Replacements already performed:
ECM(computer) - had to use old PROM as new ECM doesn't come with it.
Coolant Temp Sensor (x3)
EGR and solenoid
IAC (x2)
Vacuum lines everywhere
MAP sensor
Fuel Pump
Fuel Filter
Distributor (whole thing)
Plugs/Wires
Coil
Injectors
Fuel Pressure Regulator
Intake gaskets
Removed and cleaned all grounds
Alternator
TBI Gasket
Thermostat 195

Suggestions from any GM Genius'?

 

[retorq]

I would guess it's a vacuum leak somewhere or a shorted wire. Get an OBD1 cable and a notebook and log it real time, you should be able to see the issue pretty easily, vacuum fluctuation wildly, temp dropping or maxing ...