Cylinder 1 misfire and really rough idle causes?

[empire_eldest]

I have a 97 protege 1.5L. It is intermittently throwing a code for a cyl 1 misfire. When the weather is warm it very rarely throws the code, however the idle is still pretty rough. But now that it is getting colder the code is displayed constantly, and if I let it idle for more than a minute or two the cel starts flashing. I have replaced the spark plugs, distributor cap and rotor. Not the distributor itself. My only assumption at this point is that it could be an injector problem or the distributor itself.

I should say that as long as you keep the idle up the engine smooths out considerably and it runs great on the highway.

What would you say could be causing the cyl 1 misfire? I have been chasing this problem for a while now.

[empire_eldest]

Update: Had a mechanic check it out. Originally he thought it was the fuel injector for cyl 1. As it had low flow. Turns out all four injectors are about the same flow. So next came a compression test. Cyl 1 only has about 70psi of compression. As compared to around 170 psi for each of the other three cylinders. I next am going to take it to have a leak down test to see what is leaking from the cylinder. Any ideas on what is most common on these year/models to cause loss of compression? I'm hoping it doesn't turn out to be horribly expensive.

[Jaberwacky]

If it's just one cylinder I would tend to think that it's just a valve issue and not a ring or headgasket issue.

[Pashka0788]

Check your intake mani gasket?

[mazkam]

Valves probably have carbon build up on it. I had a similar situation with my car idling rough on start up. At first I thought it was blown head gasket, but didn't see any water mixing with oil in the radiator. After taking the engine head off and inspecting it I found that the exhaust valves (don't remember which cylinder) wasn't closing fully due to the amount of carbon build up it on the valve stem. I cleaned all the valves as the others also had carbon build up and while at it, I cleaned up all HLA's which ended up doing a head rebuild with replacement of all gaskets & seals.