1999 Mercury Mt. hesitation

'99 merc mt. runs "rough" and the check engine light comes on for a few seconds (but won't throw a code on the scanner). It gets really rough and hesitates (check engine light flickers) when going up hills.This happened about 2 months ago and had the plug wires changed,and the problem went away. O2 sensors? TPS? V6 140K. Do you think it's possibley a tranmission problem or engine only? Any ideas ??? Thanx;Mogs:confused:

If the check engine light is coming on, it should have a diagnostic code, either active or pending. You need to pull the codes. Could be a misfire, vacuum leak, loose intake air tubing, intermittent MAF sensor, etc.

-Rod