thanks, he didn't say why he didn't think it was the cats. But also, besides the TPS, I'm seeing that the throttle body has a lot of electronics in it. Could also be something like that. I hope it' not the cats, don't have the funds right now for that. Car has 186k.

 

You should have it tested using a pressure probe.
Good luck.

 

update. Mechanic hooked up his code reader and it' showing the voltages for all 4 O2 sensors are jumping around not staying steady.

 

I am not a mechanic and I don't have a lot of experience with code reading. Many mechanics focus too much on codes and forget some basic things in the process. One thing I would do is disconnect the computer and check for any corrosion on the pins and then I would go through all other harnesses and connections and inspect them. Sometimes disconnecting and reconnecting removes enough corrosion to fix a voltage drop. A sketchy ground connection could also cause an intermittent contact. Inspect the wires, blow compressed air on the outside of the sensors. They need good airflow around them. Check for minor exhaust leaks etc.
I have even heard of cars where an radio frequency interferes with the computer and causes misfires. I am not trying to scare you, just make sure the very basics are taken care of before throwing expensive parts on the issue.

Good luck. I am afraid I can't help you any further. Nonetheless, please update when you have fresh info.

 

Ok, This is getting crazy! After changing all 4 O2 sensors I continued getting a check engine light for the same codes. The week before last I was getting a misfire again on cylinder 3. I thought it was a coil pack again. So under warranty I replaced it again. It ran fine that night but the next day a misfire cylinder 3. That week, the whole week I drove it with the misfire. On Friday at work, lunchtime I decided to go out and swap the coil pack with the middle one which should change the mis to cylinder 1. On the way home i got the light with the same code for cylinder 3 & it was running a little worse with a couple of backfires. I did notice that when the car is cold it almost runs good, but as it warms up it gets worse. On Saturday last weekend it was raining all day. I was in & out a few times throughout the day. Each time I went out it seemed to be running a little better. By Sat night it was running pretty good. By the way the entire past week with the misfire I stopped getting the other codes for the O2 sensors. Sunday morning it was running great. Its still running pretty good most of the time all this past week. Just once in awhile I'll get a little sputter or a sudden rough idle. But on Sunday since its running better I'm getting those codes again P0421 & 431. I was starting to think it may be the ECU. I called another mechanic I know who I try to avoid using. He is very good but very expensive. I explained to him whats going on and said I starting to think the computer is going bad and he said he didn't think so. He said on my car they usually don't go bad. He thinks its just a bunch of small issue that all hit at the same time. But if anyone knows about these coil packs, I did notice something. 2 of the packs are "Duralast" from autozone. 1 I think is still original. But I did notice one night when the car was running in the dark I opened the hood to see if I can see an arcing or something and noticed that ALL 3 coil packs you could see a blue flashing either coming from under the packs or from inside its too hard to tell. But I do know I shouldnt be seeing this. Does anyone else know this about duralast? I got mad and looked up duralast to complain about their crappy parts, 1st she wrote back that I have to contact an autozone duralast hotline. I sarcastically wrote back asking who makes duralast parts? Duralast or autozone? She wrote back saying there is No Duralast that makes auto parts. That they hire cheap companies to make these parts for them and slap a duralast name on them. I always thought duralast was an actual company. If anybody can give any suggestions, Please! Help! Also if anyone knows about the wiring around the motor for the santa fe, I'm not that familiar with it. But I had a Buick Park ave once that had issues where it ran great when 1st starting but as it warmed up it got worse. Once it reach full temp it ran bad like a bad misfire, Backfiring etc. I finally figured out that part of the harness ran across the front of the engine block mounted to it. I unwrapped the wires as much as I could and found that the wires there were all dry rotted, insulation cracked and as it got hot they all started to arc and short, that was the problem. This issue seems to be very similar.

 

So, what now?
Did you change the coil packs that were arcing?
Was it that which was causing the misfires?

The other thing which I was wondering is ... Does your car have a MAF or MAP sensor?
Can you clean it out with MAF sensor cleaner?
The thinking is that maybe it is calling for more fuel than necessary
And therefore causing the cat codes or O2 codes???
Long shot.

 

First order of business is to replace all coils on Plugs with Denso units. Denso is the original supplier. Sure it is expensive but it is necessary. The misfires send unburnt fuel into the catalytic converter where it burns off. The resulting heat can melt the core of the converter. At that point it becomes REALLY expensive.
If you must save money find used DENSO COPs in a junk yard.

Your Buick episode goes back many years and has no direct bearing on this situation. Of course it is possible that something similar happens. It is just not likely. On the other hand the Autozone parts are highly suspect.