kmr

My advice is to go your local auto parts store and see if they can read what codes are being stored. Most of the big parts stores will do this for free for you. Just a side note, the check engine light will go on for the oxygen sensor if your battery is getting weak. You may want to get your battery checked out since you say the problem got worse when it got colder out- weak batteries don't like colder weather. Good luck!

It shouldn't be epoxied on. There maybe a dab of gasket sealant around in a couple of places. I've used a rubber mallet and gently tapped the cover loose before. If that doesn't work take a thin putty knife and go around the cover.

Yes the recommended replacement is 90K. This engine is a "non-interference" engine, which means if the timing belt breaks you don't get engine damage. Yes it is inconvenient because your engine will not run and you're stuck where you are. $400 seems a bit hit from the dealer. My dealer here in AZ charges $275 for the timing belt. $400 might be right if they are also changing the water pump which is driven by the timing belt. I'd shop around the see if you can find an independent shop that will do the job. It is not terribly complicated, it just takes some special tools. ;)