1999 Lexus Es300 System Too Lean Bank 1

[maxo898]

Hello, I have a 1999 Lexus es300 with 132,000 miles. It was running fine until i got the check engine and the trac off light come on. When i got the codes from auto zone it said misfire, so i changed all the coils and spark plugs basically a full tune up but the light was still on after i reset it. Later it said oxygen sensor, so i changed all 3 sensors. I also changed the thermostade and cleaned the MAF sensor. When i checked it another time it said system too rich. A couple of days ago i disconnected the battery to reset the system and drove it straight on the highway for 80 miles the light didnt come on until i got off the freeway into the city then the lights came back on after 10 miles driving in the city.(usally the light will come after 6-10 miles when i reset it). Now the code is P0171 System to lean (BANK 1) i read a lot of threads but i still can find the problem.i have spent over $1800 in parts and labor so please help me.

Thanks For Your time.

[lexis lexus]

I've been puzzled by this code for a few years now. As I've looked at the trouble shooting guide in the fsm, and thought about it a lot, the long and short of it is, I've decided just to live w/ it. I've not spent as much money as you, but have put in a fair bit of time. It first occurred after I had replaced head gaskets. I put in a new o2 sensor (I've a '94), replaced the rear valve cover gasket, and have even tried a different maf sensor. I replaced the egr recirculation pipe which got damaged when I did the head gaskets, but this didn't "staunch" the flow of too much air getting into bank one which is what I believe is the problem. That code is triggered by the bank one o2 sensor which is reading too much oxygen at that point (the bank one exhaust manifold). This can be measured dynamically, as a mostly negative "fuel trim" if you have a scan guage. As I understand it, the excess air might be coming from a leak in the exhaust manifold, or any where further upstream, all the way to the end of the air intake snorkle. I've never understood how a leak on the intake side of the throttle body would only show up as a too lean on only one bank, but I guess it could. I've tightened down every bolt where a leak could possibly occur, such as the intake manifold, valve cover, plenum, egr system, and probably a few others. I've examined all components of the intake system for cracks, where air could leak in but nothing has been observed.

I've never had a performance problem, and get decent mpgz, 24 around town and 29 on the hwy. I decided the seriousness of this problem did't warrant further time or money and decided to wait until it became more of an actual problem, which it hasn't for over a year.

From time to time I check codes w/ my scanner, as the CEL is on all the time. That can easily be fixed w/ a piece of electrical tape if it bothers you.

LL

[maxo898]

Thanks for the advise i'm going to try to change the intake manifold gasket and tighten any hoses. It's weird because now i am getting 2 other codes with that p0171 they are p0441 and p0446.

[maxo898]

Is the fuel air ratio sensor same as the oxygen sensor?

[landar]

There has been some similar problems with LS430's, although a completely different engine, that were caused by pinhole leaks in the exhaust 'Y' pipe near the O2 sensors. The problem is caused by a clamp on the heat shield causing rust to form underneath the clamp. Granted, it's a long shot but you might take a look.

[maxo898]

So would i need to change the clamps.

Thanks

[landar]

So would i need to change the clamps.

Thanks

You would need to remove the clamps and heat shield and visibly inspect the Y pipe to determine if any pinholes exist where the clamps were attached. Perhaps start the engine and listen or feel (be careful) for exhaust leakage.

I just looked at the LS430 post and it was code P0430 which is not what you are getting. So, you can probably forget this one. Sorry.

[maxo898]

That's fine but thanks for the advice any ways. I also checked mine yesterday and i am getting p0171 and p0441.

[JP 1970]

FINALLY... the fix was found and resolved the mystery of why my Lexis ES300's check engine light was on after several weeks along with attempts and in-depth research to solve!  NO, it was NOT the sensors at about $700 each for which I was first encouraged to change but did NOT thanks to info here.   The problem WAS fixed with replacing the two ‘intake air hoses’ [accordion boots] at about $58. each on the intake manifold.  Thank GOD for local mechanics at Embody’s Sunoco Station in Pottstown... $217. versus thousands of dollars spent in potentially un-repaired bills!!  [air intake hose part number: 696724]