97 E420 check engine light
 

<FONT face="Arial, Helvetica, sans-serif">Since purchasing the car in 2002, the Check Engine Engine Electronics light has appeared repeatedly. Initial code indicated a secondary air pump malfunction but the repairman could find no problem there. Eventually discovered the gas cap was not on tight enough. Recent occurrence was diagnosed as an air filter and some kind of control unit being cracked (cost to repair about $180). A week later, the light reappears and now the repairman says the codes are so confusing that he can only recommend replacement of an entire "computer control unit" (cost about $1700). My apologies for the lack of technical specifics. This is my first Mercedes and I love it; there are no apparent problems other than this #$%! light coming on (i.e., plenty of energy, no missing, starts right up every time); but I'm beginning to wonder if I ought to trade it in on something that won't be in the shop once a month. I would appreciate your comments and advice.</FONT>