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Having A Tough Time With P0171 Code


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First I just want to say hello as this is my first post here. I've searched the thread db and found lots of good info but Im having a hard time solving a problem and could use your help.

Our 99 RX300 has had some issues lately that I've been working through, here's a snapshot of the recent history:

Last month the CEL light lit up which turned out to be a P1135. I ordered the Bank 1 A/F sensor (Denso part) and while waiting for the part in the mail I proceeded to clean both the MAF & IACV to be thorough. About 3 days later the car began to misfire, throwing out P0300, P0301, P0302, and P0171. After investigation I found a cracked coil and ordered that as well. At this point I just parked the car until ALL my parts arrived.

I got the A/F sensor and coil in the mail and replaced them at the same time. I cleared the codes and fired it up. It's running great now and no light (yet). Within 5 miles the CEL is on and it turns out to be only the P0171 & P0171PD (which I believe means the same thing). But bottom line is that the car is running nice and smooth now.

Now Im in search of why my bank 1 is reading lean (P0171) and Im having a hellova time doing so.

So far I have run a bottle of Redline fuel system cleaner through a tank which had no effect and now I have a bottle of Techron in there now that Im trying to go through.

I have have replaced the PCV valve and inspected the hose (all is good here).

I have checked for loose or cracked vac system hose/fittings and have found nothing.

I have sprayed starter fluid around the airbox, air intake ducts/boots, intake plenum, IAC, vac lines, etc (no rise in rpm)

I have visually & audibly inspected for exhaust manifold & flex joint for cracks (all is good here)

I have removed Bank 2 A/F sensor and cleaned it with some brake cleaner just in case it got fouled during the misfire episode (no relevant codes are showing so it checks out)

I tested the IAT (inside the MAF housing) the best I could by measuring the resistance at 68F; resistance was within spec (~2200ohms)

Gas cap is properly sealing

Dipstick is properly sealed (I know but at least its ruled out)

Not sure what else to do other that start replacing the aged sensors (which could possibly be giving me a false positive). This car does have close to 150k on it.

I sure could use some help since Im about to pull my hair out.

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