last month ive had some problems starting my car. i checked out the battery and the alternator and both checked out. about a week later the engine check came up on the dash and stayed on for a day and went off.How big of a problem do u think i have?i dont want to take it to the dealer cause i will end up wasting money if they cant find anything any suggestions on what i should do. Also im looking into buying a system possibly a 10 and a 151 watt amp,any ideas on what would sound the best in a 93 lexus gs 300..thanks