There are two kinds of tests.Stored fault codes(the kind your garage cleared)dash test(none detected).And live feed tests.quite possible for stored codes to be ,well,not wrong but not complete.for eg,maybe your fault is only apparent when engine is half hot and driving at 60mph.my point is diagnostics is high end stuff,maybe 2 in 10 mechanics capable of it(dont include mself)Just clearing the fault codes will only work until the fault appears again.I'm afraid you need to find a competant diagnostic technician.capable of preforming live data sensor tests.If you do any imformation as to running conditions helps them.be precise,be accurate.The best techs are worth their weight in gold and dont come cheap.sorry I cant be more help.ps equipment to run these tests can cost several thousands.
caine
August 2008