My1991 4.9 6 cyl misses from idle to around 1300 rpm at light load. Holding around 1200 rpm it will start bucking. This doesn't happen under load. I get a 411 code from the computer "can't controll low rpm". Ok fine, why can't it controll the low rpm? What should I be looking at?
Fule pressure is in spec, has a new fule filter, new plugs, wires, cap and roter.

help!

 

I'd say it's more than likely one of two things; either dirty injectors, or an EGR problem. It's pretty easy to figure out which. Disconnect and plug the vacuum hose that goes to the EGR valve, and see if the problem goes away. If it does, you need to make a restrictor plate for the EGR valve. Let me know, and I'll tell you how. If the problem doesn't go away, then go to the automotive section at Kmart, and look for their fuel system additives. You will find one brand that unfortunately, I can't remember it's name, but it comes in a gray plastic bottle, with a copper colored cap. They should have two sizes, the small is around 12 ounces, and the large is around 32 ounces. Buy 2 of the large bottles. Run your truck so that one of your gas tanks is near empty, and go to the gas station. Pour in both bottles, and add 5 gallons of gas (NO MORE THAN THAT!). Now drive it around for an hour or so, and then let it sit overnight. If your injectors were dirty, you will notice a big improvement when you go for a drive the next day. If the problem is better, but not completely solved, you can do the same thing again.