Maybe battery cables, they tend to corrode near the terminals. Maybe ground connection? check all the sensors and vacuum hoses in the area where the work was done.
Mil code with check engine light is misfire in cylinder #5, or #6 or #7 or #8. Take it by auto zone and have them put the scan tool on it
P0305 Cylinder #5,
P0306 Cylinder #6
P0307 Cylinder #7
P0308 Cylinder #8
Maybe a bad or loose spark plug wire.
When all is said and done, more is said than done.
'97 ZJ LTD, I6 (see profile) Paid for!
Links: Kevin (AKA KOR)
for ZJ & WJ stuff,
for performance stuff. I6 performance info at Dino's jeep 4.0 performance site
Other stuff: Kevin's Roof Rack. KOR sliders, Bored 62mm TB, Blaupunkt Bermuda w/ ipod, Brembo Slotted rotors,
OME steering stabilizer, H4 headlight upgrade...