HELP - codes keep coming back and car is sluggish

**ARCTICWHITE98Z28** · 08-31-2005, 09:09 AM

I have a 98 Z28 that is stock except for an air lid. It has 76k. I bought the car a few months ago and it was running rough at all RPMs (especially low RMMSs) and had the SES light on. The car runs a little better at WOT. The previous owner did not know the root cause so I took it to Auto Zone for a free scan. The scan turned up PO131, 137, 151, and 157. These codes refer to low voltage for all four of the O2 sensors. I then decided to replace the front O2 sensors with a set of Bosch O2 sensors. The car then ran much better for about a day or two. The SES light remained on, but I figured that was because the rear O2 sensors were still setting it off. The car ran much quicker for those two days where it actually felt like 300+ HP. Man I miss those two days!!! Soon after though I have the same sluggish car that feels like 220 HP. It runs a little rough at all RPMs. WOT seems to be ok, but still not 100%. I took my car back up to Autozone today and all four codes were back. The guy at AZ suggested some fuel injection cleaner. Does anyone else have any ideas of what I should look at??? THANKS

**renips** · 08-31-2005, 10:44 AM

Originally Posted by ARCTICWHITE98Z28

I have a 98 Z28 that is stock except for an air lid. It has 76k. I bought the car a few months ago and it was running rough at all RPMs (especially low RMMSs) and had the SES light on. The car runs a little better at WOT. The previous owner did not know the root cause so I took it to Auto Zone for a free scan. The scan turned up PO131, 137, 151, and 157. These codes refer to low voltage for all four of the O2 sensors. I then decided to replace the front O2 sensors with a set of Bosch O2 sensors. The car then ran much better for about a day or two. The SES light remained on, but I figured that was because the rear O2 sensors were still setting it off. The car ran much quicker for those two days where it actually felt like 300+ HP. Man I miss those two days!!! Soon after though I have the same sluggish car that feels like 220 HP. It runs a little rough at all RPMs. WOT seems to be ok, but still not 100%. I took my car back up to Autozone today and all four codes were back. The guy at AZ suggested some fuel injection cleaner. Does anyone else have any ideas of what I should look at??? THANKS

I had the same thing only I only threw the 157 code. At first I changed out the sensor. It went away for a day then came back. It was not until I changed the Cat did the problem go away. The cats break down gradually so they may not throw a code. My dealer did this under warranty because they are covered under warranty until 80K. We even swapped out the PCM before the cat to see if this was the problem. The PCM was covered under warranty up to 80K also. The problem went away after the cat was replaced. Just so you know I tried before the cat replacement to clean the maf,injectors and I even changed air filters. Nothing until cat was replaced. Good luck

**ARCTICWHITE98Z28** · 09-07-2005, 05:29 AM

Well after cleaning the MAF sensor w/ electronics cleaner and a Q tip my Z28 is running GREAT!!! The wires did not even appear to be dirty, but I cleaned them anyway. The four codes have not come back since. It's funny how the computer threw 4 codes regarding the O2 sensors, but the actual issue was a dirty MAF.

I wanted to personally thank 2001NBMZ28 for his private message which pointed to another forum where someone else had the exact same issue which was resolved by cleaning the MAF.