I have a 91 F-150 that has a miss at idle. It is more pronounced when it is cold. I have checked the timing and it is fine. It is kind of annoying so I would like to get it fixed. Any suggestions.

Have you replaced the spark plugs lately? I only recommend Motorcraft or Autolite spark plugs in Fords. I would also replace the rotor, distributor cap, and spark plug wires, if they have not been replaced in the last 60,000 miles.

I put all new wires plugs rotor and cap about 2 months ago with no change. This truck has the straight 6 if that helps. The TFI module was changed 6 months ago.

Try cleaning the throttle body and the Idle Air Control Valve:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-7.html#post1054149

I would also recommend using full-synthetic 5W-30 engine oil--F-150s love that stuff and perform much better.

I did that too. Some one told me it was probably the intake manifold was warped or leaking. Could that be right and if so how could I check it?

Try using a leak detector solution, while the engine is running.

How do I concoct this solution?

Try Snoop, brake cleaner, or soapy water.

Never heard of Snoop. I was told WD-40 but I am a little hesitant because it is flammable. You wouldn't happen to be in South Tejas would you?

No.

If I use the Snoop do I spray it with the truck running and see if it clears the miss?

Spray it with the engine running and look for leaks.

Grab a can of carb cleaner and spray around intake manifold and fittings. Spray short shots at a certain area, wait a second or two and listen for the miss to disappear. Pretty easy, you will know when you find it.

I will give this a shot this weekend. Watch the news in case I go boom.

No boom, just spray a little at a time an listen for a change in the engine. Let us know.