I had very similar trouble with my M103 motor recently. Turned out the vacuum line going to the EZL module was leaking badly. As a result the ign timing was off at idle and it ran terrible when it became warm. It ran OK at higher revs.......if you could get it there! New rubber tube solved the problem. Have a look at the vac lines, take off any airfilters, etc to get a good inspection!

gerard