power problem with 4.3

I have a 1990 s10 blazer with a 4.3 110,000 mi Its had a complete tuneup recently - plugs, wires, cap rotor, all filters (fuel, air, transmission, etc)

My problem is loss of power. It runs great when its cold but as it warms up it has less and less power. It will get to the point where you cant go over about 20 mph. I have a cheap code reader and it says there is a problem with the "vehicle speed sensor" I have asked around and no one seems to know what this is. I checked the fuel pressure and its within acceptable limits.
It ran great and had regular 300mi trips until last week this was a problem that developed quickly. Any ideas?

Check the flap inside the air cleaner snorkel near the heat riser from the exhaust manifold. If that flap is stuck shut it'll run fine when cold, but could cause it to run like s*** when hot. Just a thought.

the flap is wide open so its getting enough fresh air.

Hmmm. As a general rule, rich conditions get worse as an engine heats up, lean conditions get better or stay near the same. Just for shits and giggles, I'd remove the air filter and lid and take it for a drive to see how it acts. You certainly won't hurt anything, and it may tell you something. Check for cracked vac lines. Pull a random plug or 3 and see if they're really black or too white.

Vehicle speed sensor could ABS related. Does it have ABS? Just fishing here....Good luck.

Vehicle speed sensor is part of the abs.

"the flap is wide open so its getting enough fresh air" is this condition while the engine is hot or cold? the flap should be open while cold to draw in warmer air from around the exhaust manifolds. when the engine warms up the the flap should close as to not allow this, at this point, very hot air to enter the throttle body. so does it function properly, hot closed and cold open?

Actually it's just the reverse. The flap closes to block off fresh air and forces the engine to draw air from the exhaust riser tube. As the engine warms, the flap opens to allow cool air in. This is on my 95 4.3W engine.

ok thank for straightening me out on that. its been several years since i went to a K&N and i have not looked at it in some time...
thanks again miss information is worst then none...

problem solved.. plugged Catalytic

thanks guys

hey just a quick question, was your y-pipe heating up with the plugged cat?

no not that I noticed. There seemed to be plenty of flow out of the exhaust too. Runs much better now, it has more power than it ever has.