I’m new not sure if I’m doing this the right way, question: I have a 1999 Ford F-150 XLT, 6cyl. 4.2 Ltr. Manual transmission and just lately I’m experiencing surging in the RPM 800-2200 up and down, if let the clutch out a little the Rpm resumes to normal until I hit the gas pedal then it does the same thing, I haven’t changed the spark plugs yet it has 288,000 miles on it and had approximately 167,000 when I bought it, truck runs smooth other than that, I change the oil every 3-6 months. Any answers I could start with, the cheapest 1st then I can try other solutions there after

 

I suggest cleaning the throttle body and IAC.

 

With over 100k on the spark plugs, change them, whether it fixes the issue or not. Use OEM Motorcraft, and if the plug wires are original, they could stand to be replaced, again, with OEM Motorcraft. Rockauto.com carries them considerably cheaper than parts stores or dealers. Coil pack should be good, but clean it up and check it for cracks and carbon tracks.

Cleaning the IAC is only a stopgap, it will eventually have to be replaced. It's not that expensive.

 

Yep, like glc said, do that and you should be in a better situation.

Are there any check engine lights by chance?

 

I recently experienced some surging on a 2001 5.4l - the surge would go up to about 1200rpm then back down every 30 seconds or so - it started all of a sudden one day.

I first tried cleaning the IAC with No Change

I then replaced the IAC and that fixed the idle surge issue. Been idling normal ever since.