I have a strange problem with a 95 Eclipse with 420A engine and automatic tranny. Everything is stock except for Cold Air Intake.
--The engine was rebuilt about 20K miles ago.
-- Problem really didn't manifest itself until after the rebuild warranty was over.
--Problem did not exist before engine rebuild.

Here's what happens:

After first starting the engine the RPM is at 1200 RPM and everything is fine----once it starts warming up and the idle comes down to 1100 RPM you can hear a misfire in the exhaust. Idle drops to 900 RPM and it still misfires----900 is the lowest it goes with tranny in Park when the engine is warmed up. If I put it in Drive, RPM drops to 750-800 RPM and the misfire is gone. RPM on the tach is steady on all RPM ranges.

Here's what I did so far:

--Compression-Cyl 1--225 Cyl 2--228 Cyl 3--226 Cyl 4--228
--Vaccum guage attached to Intake Manifold---16 to 16.5 with tranny in Park and warmed up---the .5 drop is when the misfire occurs.
--Sometimes the vacuum drop will only be .25
--All parts below were swapped with another 420A engine that does not have this problem---vacuum on this engine is 15.75 to 16.
Swapped:
Sparkplugs
Coil pack & Wires
EGR Valve & Solenoid
PCV Valve
Throttle Body with IAC & TPS
Intake Air Temp sensor
MAP sensor
Powertrain Control Module (PCM)

Nothing changed with swapping all of those parts.
There are no CEL codes either.

Any ideas?????

I tried a couple more things:
--In Park & Neutral I have the problem
--In Drive, Reverse, 1st & 2nd the problem doesn't exist
--Now in D, R, 1 & 2 the rpm drops to about 800 and even if I bring
the RPM up in the range of 1100-900 I don't experience the
problem.

If you mean to say you swapped plugs and wires with known good ones from another car, then I'd suspect the timing might be off a smidge. If you're saying you used the plugs, wires, and PCV off some junk yard car, well...

is this a definite miss, engine rpm actually drops for a moment, shakes then comes back to normal? or just a slight pause or blip in the engine note?

If it's a slight pause or blip in the sound but no real other noticable visible signs, I think it might be normal :shrug mine has done that ever since I got it, both old and new engines.

If it is visible, noticable shaking, drop in rpm's, it might be a stuck open injector since you've checked the ignition system. higher rpm's it's fine but lower rpm's it's running too rich? check the coloring of the plugs, if one is considerably lighter or darker in color that can give you a clue.

You really don't see any drop in RPM---if it is, it is very small to barely see it on the tach.
There is no violent shaking like you get if you pull a plug wire and it just sounds like a miss at the exhaust end and sometimes you can hear it from the engine compartment and see the .25-.5 drop in vacuum at the intake manifold.
All 4 plugs look the same----the grayish/browish color.

cheap fuel? :shrug that's how mine always acts, timing might be a hair off. any lack of power?

It's not the gas----I've had the problem for about 1.5 years. Lots of different gas stations.
Engine power seems to be the same as it was even before the rebuild.

What's the best way to check the timing?

a timing light

Does this procedure with a timing light sound correct?
--Connect inductive pickup to Cyl #1
--Engine should be warmed up
--Marks on cam gears should line up

Anything else???

yeah, the ignition timing is computer controlled so it won't be dead on when at 0* on the light (hopefully you have an adjustable light) IIRC timing @ idle is approx 10-15* (adjust the light to around there and it will show the marks lining up, if you can't get the marks to line up at all you have a real problem. if the timing is unusually far out (20*+ IIRC) try resetting the ECU, pull the battery cable for a few min and recheck.

when mine had this problem it was because of pitted valves and werent seating properly.
course my backfire was heard on the intake side :shrug

Did you have the misfire only between 900 & 1200 RPM?

All of the parts are from another running Eclipse(parts car) I
have that does not exhibit this problem.
Actually, when I put all of the parts I removed from the car
with the problem, on the parts car I have, the parts car still
does not have the problem I see with my other Eclipse.