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New TN User
Join Date: May 2007
Location: Nashville, TN
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A head-scratcher
I've been dealing with an emissions-testing inspired debacle for a while now. Having spent about $800 and still not having the problem fixed, I'm trying to figure out what to do next. I hope someone will be able to help me out.
Current problem: I have a P0171 code and a P0420 code.
Background: I have a 2001 Corolla S. I had a P0420 code for a while; since I lived in Arkansas (no emissions testing) and had no performance problems, I just let it go. However, over time the engine began having a few problems if I pressed the gas right after starting it up - nothing major. But in May I moved to the Nashville area, and had to undergo emissions testing to get the car registered. Trying to fix the problem, I took it to a muffler shop. They charged me $250 for an OBD check and a new cat. In the process, they told me that I needed new O2 sensors (front and rear).
I took it the same day to a Midas, where they replaced both O2 sensors ($550). They reset the code, but within 40 miles or so the light came back on. It was a P0171 code. I was at a loss at this point; reading up about it, I found out about the MAF problem. I bought some electrical contact cleaner and cleaned the amber-looking head, but I didn't know about the two wires on the inside. This didn't fix the problem, and money was tight so I left it alone. During this time, the engine began having more trouble starting cold - it would stall if I gave it any gas, and many times would stall even without any gas. It also would hesitate occasionally (more so when cold), and would be sluggish up hills. In addition, when I would go up hills, holding the gas pedal constant, the engine would surge slightly in a rhythmic pattern, about every second and a half.
I took it to the dealer to get it looked at. They said that the MAF was messed up, I needed to get new spark plugs, and that the throttle body was gunked up. They mentioned something about the fuel injector - I believe they may have cleaned it but not charged me for it (it was on the bill originally, but it was "deleted". They reset the check engine light, but it came back on the drive back home. I looked up some more information on the MAF, and found out about the two wires on the inside. I used the electrical contact cleaner on that, put it back in, and drove it later that evening - no difference. However, the next afternoon I got back in the car, started it up, and it ran without a hitch. The response to the gas was wonderful, and there was no hesitation at all. Later that afternoon, the check engine light suddenly disappeared. The engine was still running wonderfully. I went the next morning to the emissions testing, but found out that the catalyst and evap system monitors were "not ready". I had driven it a couple of hundred miles since the dealer had reset the computer, so I thought that was odd. I had it checked again the next morning (the car was still running great) - the evap system monitor was back and had no trouble codes, but the catalyst monitor was still not ready. However, later that day the car began to act more sluggish, and soon the light came back on. I took it to an Autozone to check the code - both P0171 and P0420. I wasn't sure what to make of it, but the fact that the catalyst monitor was so sluggish in coming back made me wonder if it was the O2 sensor.
So I took it back to the Midas. The technician there hooked a code reader to the car, and looked at a bunch of different stuff. He showed me the O2 sensor readings. He told me that it was acting normal, but it didn't seem normal for what I had remembered about normal O2 sensor activity. Idling, both sensors hung around 650 mV. When he revved the engine to about 2500-3000 rpm, the first sensor would flip between 250 or 350 mV and 650, and the other sensor would stay around 650 mV. He said that they were switching back and forth like they should. There was no engine misfiring. He then told me that it thinks it may be the catalytic converter. He said that he thought it was a universal one, judging from the price they charged me, and that a slight misplacement ("a few millimeters") can cause it to throw a bunch of codes. He said a direct fit catalyst would have been better. After I got back, I cleaned the MAF again; it hasn't changed anything, at least not yet. The car starts up fine, but it is somewhat sluggish. It also does the strange rhythmic surging up hills.
Anyways, between the catalyst, the O2 sensors and the MAF I don't know what to think. It's been very costly thus far, and I don't have much more money to sink on this. I realize the MAF sensor is the most common perpetrator for these Corollas, but I don't see any connection between the MAF sensor and the P0420. Sorry this is so long, but I feel like the devil's in the details here.
Last edited by KellenH; 08-11-2007 at 09:11 PM.
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long story short (from what I gather) you replaced the cat, O2 sensors, cleaned the AFM and you still failed the E-test. 
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