I searched through all the misfire threads, but mine is just a little different.
This is a 96 Avenger 2.5 The engine is used from Cherry Auto in Ohio we installed about 4 years ago it was supposed to only have 30,000mi.
It has a misfire on cyl 2 for just about 30 - 40 secs after a cold startup. This car has been setting now for about 2 years only being started occasionally. Has a full tank of old gas that I put in some stabil & fuel injector cleaner.
Fuel pump went bad, so that is new and I sent the PCM out to get repaired/checked when it wouldn't start(it checked out no problem).
So I put on a new cap & rotor, funny that seemed to fix the problem for the first day then right back again. Car runs great after it warms up for a minute.

 

Have you replace the wire set and spark plugs? Your misfire on cold start, could be a t-stat thats open not closed, or temp sensor is out of range and allowing the engine to go into close-loop until it wants too. You could have carbon on the valve seats. Maybe putsome decarb in the engine and let it sit for 6 hours before starting. By the way it will smoke a lot, someone may think there is a fire, thats how much it will smoke.

 

I haven't tried the wires & plugs, I wasn't ready to take off that dang plenum yet to do so. I thought I'd try that Seafoam stuff I read aboutin some threads here, would that work good in the cylinders to soak? If I have to take off the plenum I suppose I'll replace the t-stat. Is there a way to test the injectors as well? I believe I still may have the original set of injectors & fuel rails from the old engine.

 

misfire is normally spark/plug/wires/dist troubles ....plugs aren't that bad ... other thing to look at is see if there is oil in the plug openings ...

 

This thing can drive ya crazy...today it starts & runs beautifully w/no missing. I stopped at autozone & ran a half can of the seafoam thru the pcv hose & dumped rest in tank & now it seems to run even better, so i guess I need to just keep driving it till I burn out all that bad gas & see how it does.

 

Dang it acted up again this morning, same thing misses for about 30 sec's, then if ya rev it a little it smooths out & runs fine. I guess I have to take that plenum off after all. What all should I maintain while it's off?
I figure;
-pour some decarb in the cyls & soak.
-new plugs
-new wires
-change thermostat
-check injectors-maybe switch injector on cyl 2 with one from old engine.
I don't want to change dist if I don't have to, that suckers expensive.

 

One more question on this one.
I dug out the old injectors & fuel rails from the old engine that was blown, and noticed the fuel rails are not the same design as the one on the replacement engine. The old fuel rails were round & the others are square. The injectors look the same, but won't know till I take them off the car & try to read any part #'s on them.
Question is were there different rails used on same year or am I dealing with an engine from a different year?

This intermittent miss is driving me nutso.

 

round rails are 95/96 / square rails are 97