4.3 throttle body missing at low to mid RPM

"Michael Rothwell" wrote in message news:sIOdneXB2 snipped-for-privacy@comcast.com...

OK, try this. I believe on that engine there is a vacuum controlled EGR valve. Try unplugging the vacuum hose to it and drive it. See how it goes. If it runs better your problem is the valve and/or the exhaust partialy plugged. That valve is there for a reason so dont just leave it unplugged, buy a new one. Muffler shops can check the cat for being plugged. If they say they cant check it, only replace it, go somewhere else. If you arent too strapped for cash replace the plug wires if they have alot of miles on them.(after all you said it like to eat plug wires) There is a single injector on a TBI. If the above didnt help you might have low fuel pressure(bad pump or fuel filter). Usually low pressure will cause a hesitation right of idle because it needs alot of fuel when you take off. Your discription of the problem doesnt exactly match that. The roughness off idle while cruising sounds like it could be the EGR. I would look at the EGR and exhaust first. A plugged cat will cause a very noticable loss of power which sounds like your problem and could contribute to too much exhaust going through the EGR into the intake causing your roughness. To avoid speeding money on the EGR if you dont need it have the exhaust checked first. The EGR can cause a loss of power but it sounds like your is much worse than that. If there is a problem with the exhaust fix it first. Then if it is still rough off idle try unplugging it again, if it smoothes out, replace the vavle. Let us know and good luck. P.S. I am not positive it has a vacuum controlled EGR, but fairly sure. It is possible it doesnt even have an EGR. Most vehicles do but not all. Sorry but Im not that familiar with that truck. I think the port injected trucks are the only ones with the electronic EGR. I'm sure someone here would know for sure and could tell you exactly where it is located.