Nuckingfut

So my wife's '99 RX300 with 145k miles decided to throw me some engine code love this last week. It started out with a P1135 (Bank 1 A/F Sensor) and some other associated codes, so I told my wife it would be ok if she drove to work and back for the next week while we wait for the ordered part (Denso sensor) to show up.

Well, she drove the entire week w/o issue and then two days ago she comes home saying the car is running like crap. I proceed to test drive it and its misfiring like crazy (cel is blinking). I go pull the codes and I get a P0300, P0301, P0302, P0171, and of course the P1135. So I decide its probably time to change out the original spark plugs (yes the originals.....slap me now ) which are probably causing the misfires. I grabbed some NGK Irridium Lasers for $7/ea at Kragen and swap them out and fire it up. Chug...Chug..Chug..Chug!! Crap! its still misfiring.
I proceeded to scratch my head and consider the other possibilities. I decided to play with the coils in hopes to rule them out of the equation. Since cyl 1 & 2 were misfiring I switched cyl 1 coils with cyl 6 and swapped cyl 2 with cyl 4 (did I lose you?). I was expecting the codes to follow the coils at this point but they didn't. This time I got P0300,P0301,P0302,P0303,P0304, and of course P1135. Now Im scratching my head as Im sure you are

The only way I can explain the 301,302, and 304 is that I've got maybe bad coils AND something else going bad in cyl 1 & 2 (ie. injectors) but Im definitely confused as to why Im now getting the P0303 when I before I hadn't.
So, at this point I decided to individually check each coil to see if they are working. I did this by pulling out each coil (while connected) just a bit while the engine was running. Clearly able to hear the coils snapping I could confirm that all but one coil was functioning. I stopped the engine and completely removed the bad coil and found that there was a hairline fracture in the tube (this was the coil that originally came from cyl 2). This one will be getting replace! I went ahead and ordered 2 coils from Toyota (Denso#90919-02234) so I'll have extra on hand. The coils and the A/F sensor are scheduled to be here tomorrow so I'll wait to get the two components installed before I try to pull more codes.

So after all that Im left wondering why (if only one coil is bad and I've got all new plugs gapped to 1.1mm) I've got all these misfire and lean condition codes?
My wife runs local 87 octane which might be a contributor so I've filled up the tank with 91 octane along with a bottle of Redline Fuel System Cleaner of course I can't run it through the system until I resolve the misfires first.
Bad gas? maybe.
When the a/f sensor went out was the fuel management system not able to deliver proper a/f ratios for around town driving thus causing fuel system fouling? maybe.
The order of these symptoms sure sounds like a domino effect of either bad gas, a/f sensor going out, or a combination.

I will add that after the misfires occurred I spent time cleaning the MAF (also meaured the resistance which was in spec), IACV, and PCV valve which were all in pretty good shape to begin with.

Any thoughts on the matter would be really good to hear as Im starting to get a bit frustrated with this little egg.

salimshah

Too many things to start on a logical thread.

I would clear out the codes and have them read on the first occurrence of CEL.

Salim

code58

I agree with Salim- you need to clear the codes and see what comes up 1st. You'll chase your tail forever with that many codes, most of which are probably not gonna come back. I will say one thing- the P1135 is specific to the heater in the A/F ratio sensor. It's not the sensor itself and would have no affect on the running after about 15-20 seconds of running and very little then. Unless you have other fault codes on that sensor, no chance of it being any part of the problem.

I very frankly would pull the coils and take a really good look with a magnifying glass if necessary to see if you have more that have hairline cracks. By 145k mi that wouldn't be uncommon. Just because you hear the crack of the coil doesn't mean they don't have hairline cracks too and once on the spark plug, are jumping spark and misfiring.

Nuckingfut

I've cleared the codes prior to each time we hooked it up to the OBDII meter in the past.
At this point Im still waiting on the 2 coils I ordered (supposed to be here tomorrow). After I get the one bad coil replaced I'll report back on results.

Another thought I had yesterday; I recently installed a fresh battery which I believe to have exposed these bad components that were probably barely working with the lower voltage supply of the old battery. Now that its getting proper excitation it probably fried the brittle component(s). I kind of laughed when I looked down into the spark plug port of cyl 2 and saw arc brazing all along the wall right where the coil hairline crack was probably sitting.

salimshah

Bad is it may seem .. the clear tell tale signs are much easier to diagnose than those hard to pin down gremlins.

You are on the right track by taking care of the first reported problem fixed first and working your way out.

Salim

Nuckingfut

I feel like a one man RX commando fighting my way out of Engine Vally and Im down to my last round of ammo.

Nuckingfut

OK, I've installed the a/f sensor and the new coil. Car is running smooth again. I reset the codes by pulling fuse & neg on batt. After 10 mi the CEL is back on. I cruzed by the garage to get the code, down to only 2 codes. P0171 + some associated code. OK so I'm still lean somewhere. Could it be an air leak, a vaccum leak, or maybe a clogged injector. Hmmmm. Any ideas?

Lexmex

Let me know what that other code is, i.e. that associated code. Keep in mind, you may have to run some fuel injector cleaner through it to clean up anything left over after the raw fuel got dumped in there.

brianlayla

A lean p0171 code is very common on the rx300. You need to buy a new mass air flow meter. Lexus probably stocks it. Its very easy to change. Be sure and disconnect the battery for a while to clear out the learned values. Good luck!

Nuckingfut

I thought about that after I left the garage, should'a gotten specifics. Anyway, yeah I've got a bottle of Redline pumping through there (down to about 3/4 from full) so we'll see if that has an impact after the tank. I'll get the other code in the morning (after I have re-cleared the codes again).

Brian, the MAF was cleaned and checked at the beginning of this fiasco and it checked out. But with that said, I won't rule anything out.

Update in a few....

Nuckingfut

Well, after running through a fuel tank of premium w/ redline fuel system cleaner the engine CEL light is still on (code P0171).

The car runs great now but having that engine light on keeps me up at night.

At this point I guess I could run another bottle of fuel system cleaner through it or even take it to the local garage to have the system professionally cleaned.

Any thoughts on what I could do next before handing over my wallet to the mechanic?

Nuckingfut

All this time I was under the impression that a P0171 meant 'lean condition', nothing more. Well after looking up the code list it turns out that it's a lean condition specific to bank 1. This is helpful info.

Anyway, my mechanic believes its a vacuum leak an not the fuel system itself (i.e. injectors or plugged fuel filter). I guess I'll spend another $50 to get it on the diagnostic computer that can better pinpoint my little problem.

Nuckingfut

Lexmex, I forgot to answer your question. The two codes are P0171 & P0171pd (which Im assuming is basically the same code).

Lexmex

Having the pending P0171 and the full P0171 is key for me. If you had the P0171 without pending I'd point straight to a real issue with the MAF sensor alone. I'd attempt disconnecting the battery cables and letting the vehicle reset itself if you haven't already done so. The dumping of the raw fuel on a misfire can cause a small bit of havoc with the A/F sensors, thus triggering a lean condition. The P0171 pending is a key characteristic of this, because it's just enough to trip the P0171, but not one of the more characteristic A/F sensor codes, like P1153, 1155, etc.

Nuckingfut

Remember, this all began with the bank 2 a/f sensor then along came the misfire. Now with that said, the car was non-op after the misfire so it sat while I waited for the a/f sensor in the mail. In other words, the new a/f sensor wasn't subject to a bunch of unburnt fuel do to the fact that I resolved the misfire with new coil prior to installing the new sensor.

But, now we need to remember that the original a/f sensor in bank 2 WAS subjected to unburnt fuel. What would be my best bet at cleaning the bank 2 sensor to eliminate this variable from the equation?