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Discussion Starter #1 (Edited)
So....

2001 RAV4 with 178K miles on it (4 cyl). I have owned it since 98K and no issues until now.

I have done a bit of searching and tried a few things, and am looking for suggestions on possible issues to check into (how to check them) and other input I have not thought up would be great.

History of the problem. So I live in the Chicagoland area and am subject to emission testing. I cannot get the CEL to go away, and if I reset the CEL Code (disconnect battery method), it goes away for a bit but comes back probably 10-20 min after the engine looks to be fully warmed up. first noticed it starting on a cooler morning, and now it comes back on after resetting the computer once engine is warm. A few other things to note after resetting the battery, idle is very rough for the first 5-10 min of driving (starts high, then drops to about 500 rpm and gets rough... then balances back out around 800 or so and feels smooth).

I went to autozone and they pulled a P0171 (Lean Bank 1). Went to a few other places just to verify as I don't always trust the "kid behind the desk" with the computer but every time P0171. Not pulling any other codes (no P0174 along with the P0171).

So, to start with the low hanging fruit and having some background in cars (used to autocross a 4th gen honda prelude, did my whole H23 to H22a engine swap myself with some help from people with the right tools), and then working on my 2010 WRX Wagon (so I have both SAE and Metric sockets/wrenches).

First Attempt:

1. Pulled MAF sensor and clean with 98% Alcohol and he very tip of a paper towel (Very gently i used this method a few times on the MAF on my WRX as I used an Oiled K&N Filter). It was covered with crud but looks great now).
2. Replaced the air filter as it was dirty and time to do it.
3. Visual check for any vacuum leaks (anything disconnect, any visual tears, pinched a few lines while engine is running to see if that effects RPM/performance)

Put everything back together and disconnected + Terminal for 5 min, reconnect and light is off. Came back on after about 30 min of driving.

Second Attempt:
I did not replace any O2 Sensors in the roughly 80K (5 Years) of owning the car, and past emissions system issues with my honda were resolved by replacing the O2 Sensor, so I went that route.

1. Replaced both Left and Right upstream O2 Sensors yesterday (eff that Radiator fan placement too btw!!!! makes it impossible to get my O2 sensor socket onto the passenger side sensor).
2. Disconnected + Battery Terminal for 5 min

Put everything back together and drover for about 20 min before light came back on. Just confirmed it is still a P0171 CEL.


Next Steps / Thoughts....

From the research I did, the things I have done should have covered 70-80% of the common causes of this issue. So now I get to play in the fun WTF zone of possible issues. See below and if I am missing something simple/basic please yell at me!

1. Fuel Delivery System - injectors gummed up? I ran 2 bottles of injector cleaner (2 full tank fill ups in last 4 weeks, 1 bottle each fill up). Maybe the fuel filter is clogged or the injectors are starting to go. I don't have FPG (Fuel Pressure Gauge) but autozone has lots of loaner tools I can probably get access to. Would I connect that on the Fuel rail and what pressure reading would I be looking for to determine if there is an issue between the tank and the injectors? Maybe injectors going out, but I feel like that would effect performance a lot if a single injector would start going out on me... and probably causing more issues than just a "lead bank 1". I could be wrong,

2. Engine Temp Sensor - I saw 1 or 2 posts about a faulty engine temp sensor messing with the calculations for A/F ration once the compute goes from closed loop to open loop. Can anyone validate this or shed any insight?

3. Intake Manifold Gasket - I can see how a damaged intake manifold gasket could cause issues as it is after the MAF affecting the A/F ratio before exhaust hits the O2 sensors, but I hope its not that because that would be quite a weekend project based on how Toyota laid out the engine bay... (I miss the massive and accessible engine bay on my WRX, and how easy it is to get to most things on a boxer layout engine). I hope this is a last resort issue. Any tips on how to test for this (visual indicators... tricks... other things... )

4. Bad MAF Sensor.. the MAF was covered in black crud... never been cleaned, but typically I don't see these go out, just need to be cleaned... I am thinking of buying a bottle of MAF specific cleaner and blasting the heck out of it (used to do that on my WRX till I ran out and just started using alcohol). Maybe I didn't clean it as well as I needed, but I took a bunch of crud off of the 2 prongs and the little red/orange dot... maybe Alcohol is bad for this type and I broke it as a result...

5. Missed Vacuum Leak. Perhaps I have a vacuum leak I failed to identify in my previous 2 adventure under the hood... Any tips for testing other than getting a pressure gauge (I would need to borrow a gauge, and also get a readout of the lines and what levels of pressure they each should be at).

6. Exhaust Leak Prior to the downstream O2? I could see how that could affect those readings, but I feel like that would probably throw a different code...

7. Downstream 02 Sensor (I hate getting to this one on other cars... maybe Rav4/Toyota engineers made it more accessible for getting a wrench in to break free, and for getting the PB Blaster to soak in....

8. Throttle Issues - if the TPS had gone bad I belive that would throw some different codes... I could probably try to clean out the whole throttle body, but I am not sure how a gummed up throttle body would cause a "Lean Condition"... I would have thought less air = rich... more air = Lean.

9. Something I have not thought of? If the Distributor/wires/plugs are all getting old (they probably are) perhaps I am not getting complete burns and that is throwing something off... I feel like I would be dealing with other issues though if that was the case (Knock or Detonation or fireballs out the back...)

I hope I have given enough info... any thoughts? I alway post full results once issues are resolved, and all steps along the way taken so others can benefit in the future.
 

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Discussion Starter #2
more digging... going to try to test/clean the PCV Valve/system tonight, and get some actual MAF cleaner and blast 1/2 the bottle to ensure there is no way anyone could say it's not "clean"....
 

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the saga continues....

Pulled MAF full cleaning with MAF CLeaner.
Pulled PCV valve, it seemed to move but not too freely... cleaned with PB Blaster, and then blasted it out with Throttle Body Cleaner. Thing is moving very freely now.

Reinstalled everything, reset the computer (disconnected + battery cable for 5 min).

Drove for 15 min today and then light came back on...

tonight checking for exhaust leaks.
 

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Years ago (carbuereted cars) we used to spray gumout around any exterior areas where there may be a vacuum leak. Saw an increase in RPM when spraying near the vacuum leak. Have no idea if this will work on a modern FI computer controlled engine.
 

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Just my two cents, I don't think your MAF is bad. If your idle is OK, make sure your air box is closed/sealed correctly around your air filter. If it's broken or not sitting correctly, or loose to any degree, this can goof you up. Also, there's a good chance one or more of your injectors aren't working to spec. If their voltage is low, you can incur this code. Beyond that, I'm stumped since the code is pretty generic. You could buy a cheap MAF and see if it goes away. I don't recommend them, but fleaBay has plenty under $20
 

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yeah... I am thinking that I should get the following and load Torque on my Android Table to try and get some live sensor data. I apparently already blew money on the upstream 02 sensors (well, 178K, they would have gone out soon probably... or at least ill keep telling myself that)... so it would be great to get more in depth info about what is being seen by the engine.

BAFX-Products-34t5-Bluetooth-Android (cannot post link, but its a well reviewed Bluetooth enable ODBII reader that connects to a table and can give live sensor data.

I will check for any exhaust leaks tonight near the CAT and Downstream 02 sensors. If there is nothing glaring, time to get more insight from the BAFX + Torque app.

Im really getting stumped, and my tags have now expired and I cannot get new ones without the emission test... thank you Chicago!
 

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so.... the Torque App is amazing! but i need to learn how to use it.

What would be the widgets/graphs/meters to load on the dashboard to monitor in regards to trying to find the issue for the P0171 (Lean Bank 1) code.

I would think Vaccume, O2 Sensors, MAF Sensor, Engine Temp Sensor, Air Temp... maybe Fuel Trim?

Plugs have not been done in a while (i got the car just under 100K, and @ 178 now and never done them so they could be origional), so I orders new Iridium Denso plugs and coils now as that is just good maintenance... maybe that will do it (doubt it though, I would think that would throw a misfire code)
 

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Grimy plugs won't necessarily throw a code, unless there is zero spark causing a misfire with the coil. Plus it's a different code too (I just went through a coil change) The iridium denso plugs are rated for 100k miles so yeah it'd be a good idea to change them and also make sure there is no oil on them. If there is, you will need a valve cover gasket too.
 

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Any news on this issue?

Hello 1nschultz, I was wondering if you got your issue resolved? I too got this same fault on my father-in-law's car, it's a 2002 Rav4 2.0 4WD. Also cleaned MAF sensor thoroughly just like you did, no luck. Strange thing in my case is the codes appeared after changing the catalytic converter, since the last one broke. I was so happy to get the new catalytic converter in and thought that would get the car running fine again, but now I'm stuck with this P0171 and P0174 both left and right bank. Would be great to hear if you resolved your issue and how.
 
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