1994 GMC Yukon 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'?

[rsulliva]

Got the truck to throw a code 16 according to my vin it means: DIS fault line voltage was low for 2 seconds when EST was disabled.

 

Any ideas on how to trouble shoot this one?

[rsulliva]

Found an identical PROM and installed - No change. Rerouted plug wires away from everything electrical just in case and retimed to 0 degress when comp is unplugged (runs about 30 degrees advanced when warm and comp is under control) - No change. Also tried 2 and 4 degrees advanced - no change. Have noticed that when it is running bad, it will pull a dollar into the exhaust every so often, and then if shut truck off and immediately restart it runs great and doesn't pull dollar at all. Almost like a complete misfire. Timing light also seems to show a lack of fire as the light will flash about ten times then seemingly skip a flash intermittantly. It does this on all plug wires cylinders. Any suggestions? Working on getting an ALDL Cable.

[grampadirt]

Get an ALDL cable for sure,then the TunerPro RT program.You'll have to add some info to it so it can monitor your particular truck,have your ECM # & PROM #(actually four letters)handy so you they match your setup.That and ALLDATAdiy has helped a lot over the last couple of years.Here's a screen shot of TunerPro RT in action....



You might notice the engine speed is low and the voltage is also low.....I had just turned the key to start the engine and hadn't yet started,hence the low rpm & voltage.