95 e320 wagon check engine troubles

[goingjap]

95 E 320 with 120k miles. Have had car and serviced since 45k. Replaced wiring harness last year. Octbober 04' check engine light came on took to dealer replaced air temp sensor. November 04'check engine light back on took to same dealer cleaned the egr tube (said egr valve was functioning properly). Two days later check engine light back on. Nov13 2004 Dealer says these are un related and we are waiting for new diagnosis. I beleive must be a root problem that has not yet been fixed and we are fixing only symptoms.

Any ideas of how to get this properly fixed?

Also, how do i reset the check engine light to make it go out for a few days?