1987 F-150 XLT Lariat, 4WD, 166,000 miles. Just started a bad vibration at any speed, 25, 40, 65, doesn't matter. Only when accelerating or travelling. Let up on the gas and it goes away and feels smooth again. Seems to have started all at once and not gradually.

Any ideas would be greatly appreciated! email: bwduerr@yahoo.com

Thank you very much from snow-buried Vermont!

 

Sounds like a misfire under load.

Almost always a secondary ignition problem. Usual culprits are plug wires, plugs, and coil.

How old are the plug wires? Plugs?

Steve