Let's see. You have the timing all the way one way. The idle has gone up to a point higher than normal. Sounds to me like you have it advanced too much. There once was a time when a good mechanic could tune a car by ear. They knew just how much to move this and that to get the car running good. I used to do it. But nowadays, you CANNOT tune by ear. With your vehicle being a 1998, I would say that with your 'manual' timing set where it is, the ECU is doing everything in it's power to minimze any damage that could occur in it's current condition. This could mean pulling the timing back alot farther than it would normally. Increasing your injector on time, causing your mileage to decrease. Is the vehicle running warmer than normal?? If it is, you could be looking for trouble. Noticed any unusual popping of backfires from either the exhaust or intake?

My suggestion would be to put the timing back where you found it originally. You'll probaly find that unless you do some SERIOUS power modifications to the engine, the normal setting will get you the best overall performance. Like it or not...