I'll try to keep this short , but I've searched and searched..
I had two o2 codes throwin' the SES, p0157, and p0153, bank 1 and 2 position 2 sensors low voltage. I replaced them both, but the codes popped back at least 2 times, then went away and havn't been back.

I started to notice a rough idle, and figured I'd try simple stuff first before really tearing into it. It's rough. Not musclecar rough, something is clearly not right. It just never ran like this before. I had a p0300 code stored once, but it went away, car still runs the same. On my scanner, I could see random misfires showing up at idle only, on most cylinders.

The last thing I replaced on it were the o2 sensors. I replaced them all as a matter of precaution, but this problem didn't show up until several weeks after. Could they actually cause this?!? They are switching normally every time I watch them on the scanner, so I can't see them being the problem.

I ran some fuel system cleaner thru it, no idle change.
I replaced the plugs which were only 2 years old, still rough.
I re-installed the stock tune stored in my Predator, still rough.
I cleaned out the TB(stock) and the IAC, AND the MAF.
The MAF is a screenless SLP, but it's been that way for 2+ years, and it JUST
started doing this. Again, no change.
Fuel pressure is where it should be for a mostly stock car.

I'm getting ready to replace the intake manifold seals to see if that does anything. it idles like it has a vacuum leak, worse when it's warm, yet I can't hear or find any vacuum leaks. I know the LS type engines had a problem with the intake seals in the trucks, I've replaced a bunch, but NEVER seen an F-car ls1 leak.

I am tearing my hair out with this one, if ANYONE has experienced this, PLEASE post. I can post whatever data you need from the scanner, but I'm not sure at this point what would be important to list.

Car is a '99 Trans Am, Magnaflow, SLP lid, k&n AF, SLP MAF housing ends, Fuddle 3400 stall converter, Predator tuned, Crane Cams wires, tr55 plugs, and a 160 stat.

 

po153 -B2 S11 Passenger side front O2- For fueling

Po157 -B2 S2 Passenger side rear O2 - For cat performance

Dude, both sensors on your passenger side are not switching enough. I didn't see if you had LTs or cats? At any rate the leak you need to find is in or around those sensors. Which sensors did you already replace? If you swap em' pass to drvr and the code stays in one side well, that further points to a leak around that side. Now if the code shifts to P0133, and P0137, respectively, then you have a bad sensor. If you still have all stock exhaust, then what wiring? Anything chaffed, pinched, burnt?

 

Sorry Doc, I recorded the codes wrong, it was p0157 and p0137. Low volt. on driver and passenger post-o2.

I still have the stock y with cats.

I don't have the freeze frames handy, but they both set at the same time, every time they set. According to my schematics, the two possible circuits have nothing in common. No common ground, nothing, except for the PCM. I know better than to throw a PCM at it without exhausting every other possibility.. I've looked all over for a possible wiring problem, and havn't come across one. Either way, the codes have gone and havn't been back for a while. Neither one would have an effect on engine performance anyway.

My two theorys
1. Possibly the Y-pipe connection at the converters isn't totally sealed. Enough to not be audible, but enough to cause some o2 confusion. (I removed it to get the trans out for a converter swap.) I'll put it on the rack tomorrow and check that.. That might explain a low voltage on both sides, AND cause problems with A/F control due to an 'air' leak before the pre-cat o2's, but are they really THAT sensitive? I'd figure any leak big enough to cause a problem like that would be audible.

2. Intake manifold Vac. leak. I know the early GenIII's in trucks had a problem with them. Sometimes they set an SES, but not always. Even if this was my problem, wouldn't I see something more along the lines of say a P0171, and/or P0174, lean bank(s)? They didn't always show up with a can of ether or propane either.

Any ideas pop in your head, I'd love to hear 'em! I'm getting frustrated!!!

 

Do you fuel trims support adaptation for lean burn?

 

I wonder if your cats are clogged??? The rear O2's are there for detection purposes only. Even if they reported nothing (weren't there), the car should still run the same. If you're not getting any audible leaks in the exhaust, I doubt your allowing enough air in to screw up the front O2 calculations. However, if the car can't 'breath' right, that could cause it to stumble around idle and feel down on power (which may be harder to notice after a converter swap). Considereing the back O2's are the ones sending the error, I'd check the cats. It's just odd they both came on at the same time...

 

thanks for your input guys, I'd do the same for you! I think it might have been a bad tank of gas. I filled up at a different Mobil, and it does seem to be better... You'd figure with premimum fuel, this wouldn't happen!