Rich3fan

I'm getting a P0420 code, so I'm pretty sure I have a bad sensor. The problem is, my idle is all over the place and I can't pinpoint the problem. I have an A4 car so the T/C was not always locking up either. Can a bad o2 sensor cause this? I used autotap to clear the code, and while I was looking at things I saw about 84 misfires on # 7 during the time I was scanning. I pulled the plug; it looked relatively clean, and after I reinstalled, no more misfires. I did a PCM reset and an idle re-learn, but still have problems. No other codes are being set. Any ideas anybody?

IRACE2

What exactly do you mean by your idle is all over the place.What does it it jump up to? How long does it stay there? What does it drop down to? It sounds like a vacuum leak though.

Z28LS1camaroguy

iTrader: (3)

YES, it can cause the car to run to rich or to lean. causing a jumping idle, also check the fuse box closest to the front of the car its a 20 amp fuse that might have blown. i found that out the hard way when i bought brand new sensors and still didnt fix the problem.

Cld069

iTrader: (2)

One thing I have learned is that if a code is brought up, like a bad o2 code, it doesnt always mean the o2 went out and thats it. Something else might be causing that o2 to go bad so the problem could be elsewhere. But agreeing with above, it it doesnt go into closed loop then engine could run rich or lean affecting idle speed.

monicaz28

iTrader: (5)

True true. o2 sensors can definitely cause your idle to be messed up, but you should look at what might be causing the o2 sensor to be go out.

NHRAMAN

iTrader: (1)

IF you still have the EGR...do yourself a favor and check the O-RING on your EGR tube where it goes in your Intake Manifold on the top front of your engine behind your Throttle Body and your MAF...mine was old and I replaced it and it seals good now. Mine was doing the same and I couldn't even hear the sucking sound due to my exhaust.....

01350ss

iTrader: (18)

p0420 is a bad cat

Rich3fan

Thanks. Now that I'm home I can go into more detail...

First a correction: The Idle Re-learn DID help, somewhat. I didn't drive it after completing the procedure, only shifted in and out of park a couple of times, and it surged a bit more than what seems normal to me (never above 1K or below 400 rpms though). But at traffics lights and such, pretty smooth.

The car was inspected in June and emissions passed. I had the Carsound cats replaced about a year ago which would lead me to believe, as y'all have indicated, that a sensor is the culprit. FWIW, I spoke to a tech where I have work done today, and he agreed that a bad sensor can cause a funky idle. I also pulled the Throttle body off last weekend, cleaned it up real good with STP Throttle Body and Injector cleaner but didn't remove the TPS & IAC sensors. I became concerned that the chemicals in the spray might've damaged them, but the tech said it shouldn't hurt anything. I then asked him how important it is to tighten the TB bolts to 106 in. lbs; he said just make sure they're tight. It didn't take much to loosen them so I didn't go overboard when I reinstalled.

I stopped at the parts counter while I was at the dealer to get pricing on a sensor; $175. No thanks. I think an aftermarket will run about $130 which is more within my tolerance level, but headers are in my future so sims will probably be the final solution.

In the meantime, can someone tell me how HO2S #2 translates to physical location on the exhaust (driver side or passenger side), - OR - which side is Bank 1?

Thanks again everbody!

SSmokin 01

iTrader: (14)

B1S1 driver side before cat
B1S2 driver side after cat

B2S1 pass side before cat
B2S2 pass side after cat

Cld069

iTrader: (2)

thats the bad thing about heated o2 sensors, they are expensive at hell

Rich3fan

Thanks. Well that sucks! The passenger side o2 connector is much easier to reach than the driver side. Par for the course I guess.

Rich3fan

Unfortunatley I can't put this thread to bed yet. Real rough and out-of-control idle still exists, and the P0420 code is back.

I was about to buy a $60 dollar sensor at my local Autozone but I first stopped in at the shop that did the cat replacement last year. He also replaced a bad sensor and I wanted to see if he remembered which one. I was just trying to go through the process of elimination as best I could. First thing he told me was that aftermarket cats (DynoMax) don't last very long. I can understand that in certain scenarios that's possible, but up until a week ago all was well with the engine. Like I said, emissions test passed, so I think it's reasonable to expect more than 1 year out of a cat right? When I thought about it, and now understanding the relationship between the two, either B1S1 or B1S2 could be bad if it's actually even a sensor in the first place. This problem is probably going to require deeper diagnosis, but in the meantime I'm going look at the things that you guys have suggested, and the guy at the shop told me his engine specialist can plug his scan tool in for a deeper look see. He's got the Snap-On Tools scanner. If anyone's familiar with that tool, can you tell me if it'll show more than what I can see with AutoTap? I've got the old version. Also, after I scan again, can someone here look at it, or tell me what parameters to select and I'll post back the readings?

linegtdt52

iTrader: (12)

what does the p0420 code read out? cat converter restrictive flow?, need a little more info to help you out. if you have a minute pm me and i'll call you and walk you through it.

linegtdt52

iTrader: (12)

and yes bad o2 sensors can cause idle problems, bad sensor 1 sensors will cause it

Rich3fan

I'm at work right now so I can't spend time out at the car. I have to sneak a laptop out before I can hook up Autotap, but in any event, P0420 is "Catalyst System Low Efficiency Bank 1". If I've got this right, and in a nutshell, the PCM checks the output of the cat monitored by sensor #2 and compares to what's going into it monitored by sensor #1. If the ratio of out vs. in is too close (i.e. 1:1), the PCM sets P0420 and turns the SES bulb on. www.gearchatter.com has all of the codes and relative information for the LS1 listed by year. I was able to check for bad wiring...etc. while the car was on a lift for a trans cooler install, but nothing obvious.

My goal here is to avoid at all costs going to the dealer and paying $85. per hour for labor just to find out an aftermarket part can be had for half the cost of a factory part, especially if it does turn out to be a bad cat. I also have this nack for makings things waaaaayyyyy more complicated than they need to be, so just kick me in the *** if that seems to be the case here.