I have a 96 Integra with the non-vtec 1.8 5 speed. It is completely stock. I had a CEL for the downstream oxygen sensor. Didn't get around to replacing it for 2 months. Just before I did, it started a small misfire but only under light load at low rpm's. I put the sensor in and the CEL is off but now the misfire has gotten a lot worse.
The first 5 minutes of running and driving it runs great. After that (after it warms up), It misfires terribly. Doesn't seem to matter what speed but it happens under 4,000 rpm's. It stutters, stumbles and falls on its face. It does not set CEL for a misfire though.
What I've already done:
replaced complete distributor
replaced MAP sensor
plugs are in good shape but have not replaced them
I have wires but have not installed them
cleaned IAC valve
there is a sensor mounted on top of the intake for vacuum that I cleaned the carbon out of
have a fuel filter but have not changed it yet
What other things should I check or be looking at? Possibly fuel pump, injectors or fuel pressure regulator? I have not checked compression or done a leak down test yet either.
It's very weird that it runs fine cold but not once it heats up. Make me things it's something that has electrical in it that a contact is separating once it warms up. I want to be done just replacing parts so any help would be great.