I recently purchased a used 99 mazda protege with about 145k and had no issues during the testdrive. About a week or so after I started driving the car the check engine light came on and the idle started running rough. The issue continued to get worse - when stopped at a light or stop sign with the car in drive the car would idle down around 700 rpm then jump up and down and some times the car would want to lurch forward and on occasion would just turn off or stall out. I had a mechanic take a look and they said some air hoses were loose but the engine was still throwing a bank 2 code(sorry I don't have the code) and suggested replacing the cold packs and spark plugs (I assume cold packs meant ignition coil but I am not sure). They told me it would be a 450 repair my question is Do you think that would most likely be the problem? should I do the repair on my own? and if so any suggestion on where to get the parts? The protege is a 1.6 es. thanks in advance for any help.

 

It sounds like the ignition system like they said. If its not properly burning the fuel in the engine then it could very well throw a code. I don't know if that car has a cap and rotor for the ignition (my dad had a 96 1.5L sohc and it had a cap and rotor next to the valve cover on the left side of the car) but if you can replace the cap and rotor, wires and plugs that should help. I've made the mistake of leaving a vacuum hose unhooked and I had idle issues as well so I would ask what exactly went wrong. The 96 Protege had a solenoid with a Mitsubishi logo on it, when we had to get a second one. The plugs, rotors, and wires should be very easy, detecting the vacuum leak could be hard.

 

Mry: The ignition parts are easy to get to and easy to replace using basic tools. If you have never done this you should get the Haynes manual and a torque wrench. The biggest problem wrenching rookies have is tightening things too much and stripping the threads.

I think $450 for replacing 4 plugs, wires, coil pack and rotor and cap seems excessive to me. Did yo go to a dealer for your estimate? Try an independent mechanic for a second estimate. Go to an auto parts store and get a quote for the parts.

Continue to look for vacuum leaks , in particular at the intake snorkel. Bend it to see if it has cracks. If it does have cracks wrap the snorkel with duct tape. Replace all rubber vacuum tubes right away. Check the nipples where the vacuum tubes attach to. The one for the EGR boost sensor at the intake manifold tends to get plugged up with hard deposits. Insert a stiff wire and push through.
Take your time with these things and after you have done some work disconnect the Battery negative and step on the brake. That resets your computer and when the CEL comes back you have more work to do.