did you replace the fuel filter? if not i would do that and run a bottle of injector cleaner of some sort with a tank of 93 octane. my 98 started idling like crap after i bought it so i ran a tank of premium and a bottle of lucas and it helped a little. so when i went to do a full tune up i found that it still had the factory fuel filter on it. when i tipped it up to see what was inside the crap i got out of it looked like mud. so i changed it out and it cleared right up. so now i run a bottle of injector cleaner every 4 or 5 fill ups and haven't had a problem since. i also got better gas mileage after changing the fuel filter.
