Recently experienced rough running bad mixture type response with backfire and some shake. Sounds like it could stall when gas pedal applied but doesn't. Idles smooth and feathering the gas very lightly is possible. Occurred once at starting with 4 tries to get it to run properly. It happened the next day while driving. Managed to drive with flashers on to garage. Disconnected manifold oxygen sensor and truck suddenly smooth again. Eight days later on the way to changing the oxygen sensor same symptoms reappeared. Fairly thorough investigation by my mechanic didn't reveal root of problem. Problem had stopped again and truck ran for 100 kms. smoothly. Was going to change oxygen sensor but old one broke during extraction and a lead wheel stud was temporarily applied to seal opening.

The truck is in good running order with good plugs,wires,distr,cap/rotor syn.oil etc.

Anyone able to offer any help with this?

 

Plugged exhaust,either cat or muffler,has it been checked?

 

Thanks for the insight. Neither the cat nor the muffler have been checked. Will look at that. Both are fairly new. How would they get blocked if fairly new with just a few thousand kilometers/miles?