I have a 94 Blazer with a v6 vortec.  It idles rough and when I step on the gas it has a sort of gasping sound through the throttle body.  When I drive it on accelration it sort of bogs down and then takes off and runs smooth at speed.  The last time I drove it I got a code 45.  Heres; what I've done so far:

Plugs, wires, distributor cap and rotor. New MAP sensor. Cleaned out the EGR valve, tested the IAC its okay. New air and fuel filter.

Any other ideas? I am going to check to O2 sensor, but in theory if this is working then it is detecting a lean mixture, in that case what is the most probable cause?

I would appreciate any help. Thanks

 I would check for a vacuum leak. if you have done the above already. Its possible that some unmetered air is entering and causing to burn lean.

Smash

Thanks smash: I was doing that yesterday don't seem to be able to find anything. The engine idles rough and I was checking things out and there are several vacuum lines that converge into one line that runs into the back of the intake manifold that comes from some big black ball mounted in the front of the engine compartment, and when I pulled that off the engine smoothed out. Any ideas?

Thanks

To me it sounds the is running lean for some reason whether it be from a vacuum leak or a bad O2 sensor. By pulling off that vacuum line i  suspect that the computer seen a lean mixture and compensated with more fuel. To go any further i would need to look at the long term and short term fuel values to determine if it is a vacuum leak or bad sensor.

Smash.

Thanks Smash.  I was wrong before on the code, 45 is a rich mixture. Heres soemthing else though, on the back of the intake manifold by the distributor is a vacuum hose. That hooks into a small plastic junction fitting with two small 1/8" hoses and two normal size hoses coming from it. One of the normal size hoses comes around and hooks into a black ball in the front of the engine compartment. The others I need to trace down. Anyway, yesterday I pulled off the hose from the manifold to check it and the engine smoothed out. So I took it for a drive and allthough not perfect, it ran a heck of a lot better and doesn't bog down on acceleration. What do you mean about the fuel values?

Thanks