Dead Spot
 

I recently bought a 1999 F250 5.4 with 144K on it, Reg cab long bead,looks new, for a whopping $1600.00! The truck runs great except for on problem. If I accelerate slowly, it has a very pronounced bog at 11-1200 RPM. It will hit 1200 and just drop to 900 or so. If I accelerate quicker it seems to have no problem. I bought the truck from a company who had it checked out at a Ford dealer and their write up never mentions this and it is not throwing any codes. Anyone ever have this problem?

Is it possible the throttle linkage is sticking, causing this? I'd do a thorough cleaning of the throttle body butterfly valve and all its surrounding pivot and attachment points---can't hurt.

Has it thrown any CEL codes so far? It was was something the ECM monitors something should have popped up-----maybe?

Not sticking. Here's the thing, if I push the gas very lightly and hold it it will slowly rev up to 1200 and then just drop to 800 or so. Or if I am in a 25 or 30 mph zone it will drop because in that zone it needs to turn 1200 rpm. And no codes. The company I bought it from had it checked out at a Ford dealer and they never mentioned it. They probably didn't drive it and even if they did they probably never made it into a 25-30 mph zone. Maybe I shouldn't worry too much about it, but it is weird. Maybe I should check the plugs, it's got 140K and I don't know if they were ever done. Gaps are probably 70.

Wouldn't hurt to pull and check the plugs---never know how many miles are on 'em. My new-to-me '03 with 165K miles was reported to have the plugs changed at 100K (twice their life expectancy) but they looked much older.

That is an odd situation----don't know I've ever read about it here. That no one else is chiming in says its most likely not that common an issue.

Hope its nothing serious!

I would plug the egr vacuum line on top of the egr valve and see if the bog is still there