[half-fast]

Yes.. the truck has a computer box up under the dash. I located it to test the anti-knock circuit as outlined in the GM service (shop) manual.

The carb is a M4MED... it does not have a mixture control solenoid. It has a solenoid to control the accelerator pump discharge volume. When the engine is below 170 degrees (cold) the pump provides a full shot. When the engine is hot, the pump discharge volume is one-half.

I re-read the manual last night regarding the "dual capacity pump" solenoid. Since the pump only provides a shot of fuel when you actually step on the gas pedal to activate the pump, I think I can assume that it would not affect a sniffer test at idle.... so I am ruling it out as a cause for my emissions problem... even if it is bad (I think it's okay) it should not affect hydrocarbons at idle with my foot off the accelerator.

I have the GM Factory Shop Manual which describes the carburetor in detail. It is not a California emissions vehicle..... definitely has the M4MED carb.... no mixture solenoid.

I just cleared a space for the truck in my garage so I can move it inside and pull the intake to replace the intake gaskets. I can't see any other options at this point.

If there were a source of information specifically geared toward emission issues with this year/engine./carb... that might save me some grief.