[Kurai]

*cough* Honestly I'm not trying to spam the forums with my questions; I'm just trying to track down the source of my problems before I start driving this truck.

1992 S-10 Blazer (Tahoe LT), 4x4 (doesn't work), 4.3L W series engine.

Vehicle idles roughly at times, smoothly at others. Today it performed a new trick while waiting in a drivethrough: Surging high while at idle. (Wheras before the 'surge' was a surge downward to the point of almost stalling.)

Things I have replaced already:

Plugs
Wires
Distributor Cap
Rotor Button
PCV Valve
Air Filter
Fuel Filter

Things I have performed already:

Oil Change
Remove and clean IAC Valve
Inspect and clean EGR Valve (I removed the air intake plenum to accomplish this but it went back on just fine)
Removed and cleaned the hose that connects the PCV valve to the air intake plenum.
Traced all vacuum hoses to where they join and none are loose or damaged under the hood (one is apparently loose inside the cab).
Filled with premium grade gasoline
Added fuel injector cleaner

Vehicle gives no diagnostic codes. (ECHU does, but that's the Antilock Brake light, not the Check Engine Light)

Is it possible to have a Throttle Position Sensor begin to malfunction, cause these symptoms, and not give a code?