I have a 2003 evo 8. It ran fine before this hiccup. I had my front o2 sensor go out. Replaced with oem equivalent denso. Ive heard both good and bad about oem equivalent that sometimes you can get duds. Anyways now im getting a PO133, oxygen sensor circuit slow response bank 1 sensor 1. It does not idle at all unless I do it manually with my foot. And when I get it to hold at say 1500rpm it revs up and down. My guess is that this o2 sensor is crap. I know the oem one is the only sure fire way to go. But before I pull the trigger of that rediculous price, I would appreciate any input on the subject. TIA.

 

ive used the denso's alot with no issues.

do you have a afr gauge?
if so, what are the afr's doing?

 

The AFR is not constant like it used to be. It used to steadily stay at 13.9to like 15.2 but mainly in the 14s. Very reliably. Now it constantly goes back and forth between low 13s to high15s.

 

I have the x and my #2 sensor is the same except wire length. So if yours is still underneath zip tied like mine try it. I was just going to use mine the other day because of low current reading but found a mad wire just underneath rubber on top of #1 sensor bit of time little gasket maker I save 300 bucks. Still have back up

 

I only use 1 o2 sensor for engine management. Its the front sensor. The rear sensor is is the wideband. The front sensor goes fromt the downpipe at the front of the car and runs up over the valve cover. I even recently repinned and replaced the o2 sensor connector on the engine harness with a repin kit, as well as i had the entire engine harness apart recently. so i know thats good.

 

Could be you just got a bad sensor. check for corrosion in connector.

 

you sure you dont have a boost leak or something?

bouncing up and down sounds like a vacuum leak.

 

Could it be a bad iac? My rpms would fluctuate along with my afr’s when it went bad.

 

Its entirely possible the up and down could be tied to a vacuum leak. I know of one spot where this might, maybe be the case. Ill double check it. All the factory vacuum I can go without hase been deleted so vacuum/ boost leaks r super simple to that on this car visually or auditorily. Def could be the iac. Ive got a spare on if need be but I find it hard to say one way or another until I get this o2 wurking properly to see wut issues are left of any. Like i said I had non of these issue before the o2 went out. I will definitely keep an eye on and check everything that you all have stated!

 

last front 02 i had go bad ... the car ran really reach. idle, cruise... everywhere.

not sure it this is always the case... but its what happened to me on a stock car with a tune only.

 

Mine also it fired up fine just if you watched afr it was just guzzling gas. When was last time you changed your plugs????

 

New spark plgs cuz I was driving it a bit when the original o2 was bad and the plugs were hella fouled. But the new o2 came in today. Fixed everything. Idles fine. Still a bit up amd down but thats the normal up and down due to cams. AFRs r stable now like they used to be. Now my First hand experience with denso o2 is that its hit and miss. Just make whoever u got em from give u new ones until u get one that wurks. Thanks again for all the input!

 

i pulled the motor out of my sons 06....
i never touched the 02 sensor.. just unplugged it and left it with the turbo assembly.
when i put it all together... it was running really rich.

Aaron at english told me to replace the front 02 sensor... he said anytime you work around them, there a possibility they die and that it happens all the time.
he was right... fixed my issue.

glad you got it sorted out.