My car has been hesitating for about 2 months--right at about 40 mph

1999 Toyota Solara 100K miles. About 2 months ago it started hesitating--betw 1600-1800 rpm--only while giving it gas. THe mechanic could find nothing wrong. Tried gas treatment and now using higher octane gas. No improvement. No check engine light until 2 days ago. But after I double checked the oil, the check engine light went off. Took it to my mechanic's (again) who put the computer on it and got 1410 EGR Position valve malfunction. They did not think this was it so said wait a week and come back to recheck the code. I see you do have an answer that says EGR valve. So do you think if I replace that, the hesitation will go away? Is it easy to do myself or should I take it in. I'm semi-handy--car work was mostly done many years ago on my 1969 VW bug.