Hello,
My ranger has been hesitating as I accelerate through 1100-1200 RPM. It's done this occasionally for a while. It's very frequent now. It happens more when the engine is hot. I've seen a few posts asking about bucking. My truck is bucking fairly regularly under fairly specific conditions. Just one hiccup unless I'm hanging around that RPM range. I read a post saying the Idle Air Valve might be a culprit.

Any suggestions where to look?

Thanks

 

How many miles are on your vehicle/engine. This'd be the 4.0 SOHC. Are you the original owner? How long have you owned it?

Since the IAC controls idle speed in the 750 rpm range I wouldn't think it'd effect a running engine @ 1,00 to 1,200 rpm.
Does your engine cease hesitating when it's over 1,200 rpm?

My notes on the IAC include:
1) IAC Valve is the ONLY source of idle speed control. It’s VERY accurate (+/- 4 rpm)
2) Unplug IAC on a running, warm engine. RPMs should drop to 500 rpm/near stalling. Maintained or increased RPMs = vacuum leak.
3) Remove IAC and turn key. It moves only ~3/8” but DOES MOVE.
4) Unplugging (removal of power) results in IAC moving closed. Connector should have 11 volts.
5) Replace with Motorcraft or Hitachi ONLY.

The MAF sensor is said to need cleaning annually. Try that.

Plugs/wires/coil pack in OK shape? Open the hood in the dark and check for sparks.

As always, try a dose of Techron before a stint of local driving.
The PEA is said to clean injector nozzles upon shutdown so don't add the Techron before a long trip as it will be wasted.

 

Thanks for replying,
The truck has ~280K miles, the odometer hasn't worked in years. I've had it for 17 years. The only time is hesitates is when the rpm's go from 1000 -> 1200 rpms. It might be doing it when going from 1200 -> 1000, but there's usually no load on the engine so I can't tell.

I'll check the MAF and change plugs and wires.

Thanks