So i have a 2008 NA XK. p0171, p0174, and p0411 codes.

I bought the car 2 months ago as is, and am having trouble solving these codes. The car came with a new PCV breather hose and that 3 way vacuum hose between throttle body/fuel pressure sensor/purge solenoid. If the car was cold, I would get some rev hang if I revved it slightly.

If cold, it will throw a p0411 within seconds. I have never heard the smog pump run (this matters for later). I thought it best to tackle the lean codes first, with the hope that they are related to the p0411. I smoke tested and the intake pipe was leaking, and the plastic base on the EGR Valve. I replaced the intake pipe- no longer leaking. I replaced the EGR valve with a used one- this one leaked at the base too. They sent me a new one, but I put gasket sealer around the plastic base they sent me and I no longer get smoke out of there (I also replaced the crush washer gaskets on either side of the EGR valve). Lean codes remained. I got new intake manifold gaskets and the throttle body gasket, since I thought that would be a good proactive move. No change. I realized the PCV valve was squealing, so I bought a new one- no change. I smoke tested this, and this brand new part leaked out of the housing. Replaced with a functioning one- car wouldn't rev quite as high on startup, but no change. I replaced the air filter and cleaned the MAF (with MAF cleaner). While checking for air leaks, I accidentally snapped the nipple to the fuel pressure sensor, so I replaced that. The oil filler neck was loose, so I replaced that and the o ring for the dipstick.

The other day I also checked the fuse for the smog pump- not blown. I switched out the horn relay, no difference.

Rather than throwing money at this thing. and realizing that this was clearly spiraling out of control, I decided to consult chatgpt to help me interpret scan tool data.

At Idle:
MAF- ~4.5g/s (Normal?)
STFT (Both Banks)- 0-5% (Also Normal?)
LTFT- about 20% both banks
Fuel Pressure- Around 48psi on average, although it would jump down to 42psi briefly, then back up.

At 2500rpm:
MAF- 13-15g/s
STFT- Same
LTFT- Around 3% (much lower)
Fuel Pressure- a little higher

While I had been gathering this data, I think I ran the battery down a little bit. I cleared the codes with the ignition on, but not the engine. I then turned on the engine and the whole dash lit up. I figured just low battery or maybe something happened with the code reader, but the smog pump turned on for the first time since I've had the car. I tried smoke testing again and saw no smoke, but the machine still had flow.

Maybe I'm smoke testing wrong. I've tried a variety of ways. Sometimes I pull off the intake at the MAF side and seal it with a glove and zip tie. Other times I'll remove the intake from the equation and seal at the throttle body and inject it through the PCV breather hose or the crankcase breather on the other side.

At this point, the car runs normally, besides the check engine light.

Any ideas are welcome and appreciated!

 

have a p0171 and a p0420 - following this post, thank you for the smoke test information because I didn't know where to start with that even though I own a smoke tester. I will try what you suggested. Have not gathered any scan tool data either, yet.

 

Those trims imply one or more air leaks, sadly.

 

The MAF at 2500rpm is at the lowest of the range. Are you running the original spark plugs?

 

Firstly, I commend you on a logical troubleshooting path. Though you did play musical parts without the root cause being sorted, in this case I'm not sure you could have done better.
I may have missed it... did you check the intake manifold and gasket?
Is the fuel filter replaced?
You may not think it related, but the ECM constructs its data by assembling intake and outtake gases/airs: what is the state of your exhaust, right from the exhaust manifold?
Also, in addition to these codes, what is the effect on the engine? How is she running at idle? When cold? when hot?
Also, how many miles?

And lastly, you are showing 4 digit codes. Not the JLR standard of 6. In many cases, the code is simply truncated... but not in all: Somtimes, some code readers substitute a code for an unknown value.

 

na 4.2s have secondary air passages clog all the time. i forgot how that spaghetti is set up.

do you have a factory maf? if no get one from the dealer or the toyota dealer for a 4.0 v6

do you have any crankcase vacuum leaks including the timing cover? the manifold to riser green seals leak you can only find it with brake cleaner and watching the trims change

 

I bought the car in March, so I'm not sure. I haven't changed the spark plugs. I'm not sure what plugs are in there, but plan to remove them at some point and inspect.

 

Sorry for the late response, I was out of the country.

I caved and paid a luxury auto shop to diagnose the car, since I thought I needed an extra pair of eyes. Diagnosis fee was $300, but the kicker was that they wanted $600 to replace the dipstick O-ring. What a joke. I replaced that for free with an O ring kit from work, but still got codes. Total waste of time and money.

I have not replaced the MAF, but I might bite the bullet and order one for the peace of mind. The car runs ok, but not consistently. Occasionally it will have a rough start but smooth out within a few seconds. Once the car has run for a little bit, it starts up nicely. This doesn't happen every time, but cold I would say it starts roughly more often. Sometimes when I leave the driveway after a fresh start, the engine will rev up while its changing gears and then jump into the next gear. So maybe something metal is expanding and sealing better while the car is hot.

If I smoke test with through the brake booster hose, is that testing the crankcase? If I want to smoke the crankcase, should I go through the breather that hooks into the valve cover?

I smoke tested the other day using a 3 inch rubber pipe fitting to seal the throttle body (to be completely sure its sealed) and injecting into the brake vacuum line. Saw no smoke, but still had flow on the smoke machine. So, where would the smoke be going?

I have sprayed brake cleaner on everything, including around the intake manifold, no change. While those gaskets could be leaking, I did replace them already and did all the other gaskets on the intake manifold while it was out.

I replaced the fuel filter a few weeks ago. I might go the old fashioned way and use some rubber tubing to search as well. I hope to Christ that the exhaust manifold is sealed. That is not a job I want to do, even though I have access to a lift.

Is the 1GR-FE Toyota MAF the same Denso sensor? (29055-1976040)

Next time I have the car at work, I will scan with the snap on scanner. The codes I am pulling are from a cheapo scanner, so I'll try to get those 6 digit codes.

 

maf from the toyota dealer part ending in 22010.

denso’s aftermarket/first time fit mafs are garbage for at least a few years now