p0420 failed cat, covered by an 8/80 so 8 years and 80k miles.
p1129 map problem, you want to diag? you have a volt meter?
p1519 iac problem, again you want to diag? you have a volt meter?
p0505 malfunction in idle system, same thing?


the cat code is on its own, the other 3 can be related to a possible vac leak, iac or map failure,idle adjustment,short or open in wires. To find a vac leak spray the intake and vac lines with carb or brake clean if you hit a spot and the rpms jump that would be you vac leak.

Again if you want to jump in we need a volt meter and some free time.