86 150 w/300 inline carb'd 4 spd. 72,XXX miles, previously driven by an older gentleman.
When the engine is cold, it runs fine. Once it warms up, it misses at idle, and then when I'm driving it, it acts up terribly. The first 1/3 of pedal runs great, and the last 1/3 of the pedal runs fine. The middle 1/3 of pedal, it spits, sputters, misses, hesitates, backfires through the carb, etc, etc.
New plugs, wires are fine, new cap & rotor, new fuel filter, new air filter.
Engine diesels at times when shut off, as well.
Took the vaccum line off the EGR valve today and plugged it with a bolt, and it seemed to run better, but not perfect. It still missed and sputtered a little.
I'm checking the timing tomorrow and compression test as well.
Any other suggestions that may fix my problem?
I've been told TPS and EGR. What about O2's or clogged cat? Would that do it?
Thanks in advance.

 

Also, what's the deal with EFI manifolds? What do I need to do this?

 

Check the timing for sure, sounds like it could be a choke/carb problem.

 

forgot to say.....rebuilt the carb last Saturday, and replaced the gasket between the intake and egr plate. I can't get the carb adjusted right because of the miss at idle. It's getting really frustrating.

I've heard of different timing marks on this engine....which ones are the right ones?

 

Pass side timing mark.

You have a vacuum leak or your carb is too lean.

 

Exactly, my truck had similar problems and it turned out to be choke/carb related, checking timing wouldn't hurt either. I would rebuild the carb and make sure your choke is working properly, or better yet bolt a 4 barrel on it like I did!

 

Saturday: timed her in perfectly.....
Sunday: Compression test, all 6 cyls between 147-150...wow!....vaccum test, A-ok....manifold leaks, none....cap and rotor, pretty darn good shape.....plugs, gapped properly, great shape....plug wires, TWO BURNED!!!....coil, CORRODED ON TOP!!!
Could this be the fix to my problem? We'll find out tomorrow. Come to notice that the plug wires on the truck are a mismatched set, and apparently are older than what I thought. I'm buying new ones tomorrow and I'll keep you posted on the outcome.
Thanks for the help, too!

 

Sounds like you've tracked it down. Bravo

 

See if you can reach underneath the EGR valve's diaphragm housing and push the diaphragm up and down with your fingers. It should moove freely. Get a vacuum pump or suck on a piece of vacuum hose that is connected to the EGR and make sure the diaphragm is not leaky. Sometimes you can renew a testy EGR valve by cleaning the carbon from around the shaft that must move freely.

This may not be it but it is worth noting that EGR valves can cause serious driveability problems although many times overlooked.

 

Has the coil leaked?

 

Well, the wires didn't fix it.
What do you mean by "leaked"?

 

You said vacuum test AOK. Should be near 20in. and no fluctuation. Is that what you actually got?

 

You mentioned the corrosion on the coil. I have had them leak causing erratic drivability. If you have another vehicle around with a coil swap them out to see if there is an improvement.