2000 Mitsubishi Montero Sport

Need some help folks! I have a 2000 Mitsubishi Montero Sport. I had a P0421 code so I replaced the rear 02 sensors with OEM O2 sensors but still had the code so I brought it to Goodyear. First off it took them 4 days to figure out the correct parts to buy and install. Then after they replaced the two forward ones all of a sudden I get a P0300 Random Cylinder misfire code and the car runs really rough. It has no power at all and practically stalls out when at a stop lite. There was also a P0201 Injector Circuit Open Cylnder 1 code. I cleared the codes and the P0201 has nver reappear3ed.

I pulled the plug they say was bad - no problem it sparks cleanly. I put the plug back in and still poor performance. I unplug the two front O2 sensors and low and behold I have full power and acceleration again. Yes I received PO170 and P0173 codes while the O2 sensors were unplugged, but NEVER saw the misfire code again!

Thoughts?

Did they put the wrong O2 sensors in?

They are telling me the rough idle and poor performance is because I need to replace all spark plugs and wires - for $800!!!! I told them to go pound sand for that price!

What are your thoughts? I'd be interested in hearing.

Thanks in advance for the help.

strikes me as odd that all 02's would fail before the plugs and wires! A tire shop would be the last place I'd have engine diagnostics done! Is it equipped with a MAF? if so then what's it reading? What about fuel trims?
If the plugs and wires are original and the mileage is high enough maybe they are shot but they don't normally generate a lean code like that!

Thanks for the reply.

I dont think the issue is the plugs or wires, but maybe. NEVER received a misfire code ever on the car until they replaced the O2 sensors. Wires and plugs got about 65,000 miles on them. Mileage has been good - no noticable drop, no misfire codes.

Another bit of info, is that they had to have their vendor send "all their O2 sensors" since the ones that the vendor said was for the car would not fit. My guess now is that the are not using OEM parts. Does that matter at all?

Yes, I agree, I will never bring the car to a tire shop for engine work again.

Can a wrong O2 Sensor cause the symptoms I see when the O2 sensors are connected - poor power, "random misfires", hard shifting until I get past 2nd gear (no issue previously or when new O2 sensors disconnected).

I will look at trim and MAF and post my findings.

incorrect 02's could I guess cause issues if they used one meant for before the converter behind it and vice versa but I'm not sure, the misfires could like they said be as simple as needing a tune-up or the failled 02's could have washed the cylinders down, thrown the fuel curve out, etc, etc! the hard shifting is unusual too unless something was damaged or moved for access to the 02's not sure! I'd be trying to get my money back from them at this point if you feel the vehicle is in worse shape after the repairs! Take it as a good lesson learned, Tire shops do tires and alignments reasonably well, it's there bread and butter and there specialty, drivability isn't and never will be

Thanks Jeff. Leason certainly learned. The funny thing is once I unplug the O2s they installed, no more issues.

Hmmmm