93 Chevy C1500 (Cheyenne) Idle Issue

[Kin2InuYasha]

Hi,

I have a 93 Chevy Cheyenne TBI 2WD v6 4.3 Vortec that has been giving me issues lately. It's run beautifully since I've owned it but recently I've been having a problem with it idling/running.

When I crank it, it idles rough as if it wants to die, and will fluctuate between revving up and choking to death. If I can get it in gear without it dying completely I can putter around at about 5-10mph, but as soon as I ease on the accelerator it tries to die, and if I let go it will (almost) idle properly again. This has happened suddenly while I was driving, it was not gradually getting worse.

I've also noticed a delay when I depress the accelerator and when it decides to rev. I CAN get it to rev almost normally when in park, it just will not idle properly, and will not accelerate without choking when in gear.

I've consulted the Haynes Manual in trying to diagnose the problem, and this is what I've done so far.

1. Replaced the fuel filter
2. Replaced the spark plugs
3. Replaced the spark plug wires
4. Replaced the coil
5. Cleaned the Rotor cap
6. Rebuilt the TBI with all new seals/gaskets
7. Replaced the Injectors
8. Checked the Throttle Position Sensor with a multimeter to ensure proper function
9. Checked the proper voltage coming from the ECM to the TPS
10. Checked for vacuum leaks

I did not check the Idle Air Control Valve because there is not one connected, and has never had one connected as long as I've owned the truck. The only thing I can figure is the previous owner removed it and installed a manual idle adjustment, but keep in mind it's been running fine without it.

I'm inclined to believe it's a vacuum leak somewhere but have no idea where, or how to check more thoroughly.

I thank you if you read all of this, after extensive googling, I couldn't find a clear answer or anything that would lead me to more possible problems. I would take it to a shop, but for financial reasons I can't. You guys are my last hope, thanks again.

[jamesslcx]

Have you checked fuel pressure? I usually get a can of carb cleaner and spray around the tbi base, vacuum lines and intake manifold and listen for a smoothing out of engine. You need a working IAC valve on that engine though. Check engine light on? Checked 02 sensor?