List what your tune up entailed.
(Note: the tune up might not have anything to do with your car in limp mode)

Lookup all the codes and see if they point to something specific.

what would suddenly clog up the catalytic converter?
(the only reason I replaced the cat on my 91 CRX Si was the NOx level got too high to pass California smog test, no EGR system on the car to lower NOx)
Clogged air filter (or something in the tube before the air filter?)

Look for disconnected wires, vacuum hoses (cracked vacuum hoses too).
Check all the grounds on the car are clean and tight (negative battery terminal, transmission, valve cover, thermostat housing; Note: the thermostat housing ground is the main ground for the ECU)

take care,
ChrisS