Hey all, I know this is a topic that comes up a lot, but I don't have time to go through all the threads. We have a 91 F-150 with 4.9 down at the shop and are at a loss for ideas. It came in with an intermittent stumble, and we have checked and tested all the typical problems. We put in a new TPS, new TFI module, new pick up coil, new plug wires. It has no codes, and only has 60K original miles. It is a manual trans 4x4, and runs like a tiop, smooth and sweet and quiet, except for this nagging stumble. Any ideas? We are scratching our heads, and need some fresh ideas here. Like I said, we already did the most common causes of this symptom, and are running out of ideas.

 

My experience based on 26 years is if you're talking about at idle, it's fairly normal, things getting out of tune.

 

Probably just needs a good tune / tweak. Might need to clean up the throttle body, IAC, and intake stuff - maybe even the EGR. Might also be fuel delivery related or the cat might be getting clogged up some. I've noticed that running fuel system cleaner regularly and doing regular clean-up on the above mentioned items seems to help those unexplainable stumbles.

 

Thanks guys. It purrs like a kitten at idle. It seems to only be when accelerating under moderate to extreme load, and onece or twice on long decel.

 

my 89 4.9 did this, after checking the codes, wound up being the o2 sensor. put in a new one, cleared the codes, and no more problem