I have a 95 Mitsubishi Galant that I use for work.

It has been having issues with it stumbling while I accelerate for a little while now. But now it will barely accelerate at all.

The plugs, wires and air filter are 2 months old, the cap and rotor I replaced yesterday, along with the fuel filter.

I checked the wires for arcing, but saw no signs.

The check engine light comes on, but not when this issue is present. For the last 4 days the check engine light has been off, but the issue has gotten worse.

I can hear the fuel pump working before I turn the key to start the car.

Tried some commercial Injector cleaner on a whim, nothing.

Checked the Mass Airflow sensor, it looks clean to me.

The car idles fine, 90% of the time. Sometimes it drops about 400RPM and sputters but jumps right back to about a 1000Rpm idle.

It used to be that it would simply stumble at lower RPM's but when I got it above 2k it would smooth out and accelerate just fine. But now, I can barely drive the thing.

One important detail: When the engine is cool, the problem is not so pronounced. When it gets up to normal operating temperatures, the issue is severe. We thought this might be an issue with the Catalytic converter, but when we disconnect the exhaust it does the same thing.

I am going to check the TPS, Fuel Pressure regulator and the ignition coil.

Any suggestions on what I should check next?

probably a failing distributor, or more specifically the coil within it. they've been know to crack and arc internally.
the only fix is a new distributor assembly.

im assuming you've already replaced ALL other secondary ignition componants (plugs, wires, cap, rotor).

Yep, plugs and wires were replaced 2 months ago, cap and rotor was replaced last night.

Check the MAS too. Just because the sensor looks clean does not mean its working properly. The plug on it could be bad or the whole unit. Just a thought...good luck

One more thought...its a long shot...maybe you have some air in the fuel lines. That would also disrupt acceleration I would imagine.

there is no problems ever with air flow meters, unless someone tampers with them.

And you cannot get "air" in the fuel lines on a fully submersed, high pressure fully recirculated fuel system.

I have the same exact problem on my '95. Did you ever get this fixed? If so, what was the problem?