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Discussion Starter · #1 ·
Hi all. First post here, just picked up a 2005 Pilot with 168k coming from an 06 MDX with 280k. The Pilot was a great deal, so it came with some problems, which I would appreciate your help in diagnosing. The idle is rough and the revs are very low upon startup, and I pulled P0172, P0175, and P0455 codes a few days ago. They have subsequently disappeared without the idle issues doing so, but that prevents me from getting freeze frame diagnostic data when the codes are live. Any ideas on why that would happen?

I've done some significant nosing around on the Bank 1 and 2 rich codes (P0172 and P0175), but I'm wondering if there might be any relationship between the engine running rich and the EVAP system leak (P0455) code. Here's the only thing I've been able to find on that: in this thread, user AVC states
I did notice on a recent trip that my combined trims approached -25% on both banks right after a fill-up, which makes me believe there is an emissions EVAP issue, allowing raw fuel into the evap canister, which would make the canister vapor very fuel-dense, driving the mixture very rich when the canister is being purged. Even then, the PCM does not set codes. This issue may be entirely unrelated to the chronically negative trims.
Thoughts?

Lastly, here's a list of things I'm going to look into / that I am aware of as potential sources of rich codes:
1. Vacuum leaks, smoke tested and none appeared
2. Clogged air filter, next check
3. MAF sensor dirty or malfunctioning, next in line
4. PCV valve
5. EGR valve issues and dirty EGR ports
6. Valve lashes need adjustment
7. Fuel pump/filter issues, fuel pressure regulator/sensor, high fuel pressure
8. Bad or non-OEM O2 sensor
9. Bad, leaking, or dirty injectors, will perform a clean
10. BAP sensor calibration
11. Intake air temp sensor
12. Coolant temp sensor
13. Air intake tube cracks, checked once, going to check again
14. VVT solenoids, spool filter-gasket

That's quite the mountain of leads. Based on my symptoms, is there any way to narrow them down, or does anyone else have a success story with rectifying these codes?

Thanks in advance for any help and input!
 

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2006 Honda Pilot 2WD
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Easy to narrow down with that many miles and my experience (2006 Pilot with 320,000 miles). You will find that option number 6 will be the biggest contributor to your issue especially if it has never been done.

I would start with Option 11, and would clean the Intake air temp sensor (this is easy to do, remove sensor, clean with B-12 Chemtool or similar cleaner, replace sensor) as this will definitely affect the rate of fuel into the engine. Then I would change the first O2 sensors (option 8) in line. Then I would followup with option 6, valve adjustment.

Start with the simple and easy first, then go more in depth.
 

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Discussion Starter · #3 ·
Easy to narrow down with that many miles and my experience (2006 Pilot with 320,000 miles). You will find that option number 6 will be the biggest contributor to your issue especially if it has never been done.

I would start with Option 11, and would clean the Intake air temp sensor (this is easy to do, remove sensor, clean with B-12 Chemtool or similar cleaner, replace sensor) as this will definitely affect the rate of fuel into the engine. Then I would change the first O2 sensors (option 8) in line. Then I would followup with option 6, valve adjustment.

Start with the simple and easy first, then go more in depth.
Appreciate the input! I think I'll start with the valves since I'm low on funds and don't have to buy parts save maybe valve cover gaskets. When you say sensors, there's more than one upstream sensor? Or are you suggesting I replace both upstream and downstream?
 

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Appreciate the input! I think I'll start with the valves since I'm low on funds and don't have to buy parts save maybe valve cover gaskets. When you say sensors, there's more than one upstream sensor? Or are you suggesting I replace both upstream and downstream?
My 2006 has 6 O2 sensors, one for each bank both upstream and downstream. I would start with the upstream first as it is most likely to fail first. They have the most extreme conditions. On the air intake temperature sensor, the one on the intake manifold, you will often find this coated with a yellowish brown varnish. This varnish affects the voltage produced. Clean the varnish off and it will behave like a new sensor.

On the valve cover gaskets and valve adjustments: I have reused mine(gaskets) without a problem. However, be very careful when tightening the valve cover bolts on the side nearest the firewall. Do not over tighten or you will likely twist one off. Easy to do since these are the hardest to get too. Similarly, when adjusting the valves, the cylinders nearest the firewall are the most difficult to adjust based on the room you have to work and the awkward angle you have to get in to adjust the valves. This side, and the conditions present, is why it took me 4 tries to get near perfect rather than do it right the first time. There are a few more details in some of my other posts.
 

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No experience with those specific codes, but a clogged or stuck open EGR valve will definitely cause a rough idle. EGR valve is easy to get off and inspect/replace, two nuts, maybe 5 minute job. Part is like $100. Way easier than valve adjustment ha ha.

Not sure about the PCV valve causing rough idle, but it is cheap and easy to do also.
 

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Nobili spiritus embiggens pequeño sparus tyre.
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Part is like $100. Way easier than valve adjustment ha ha.
Or get a good one here for less than half that.

2005 HONDA PILOT 3.5L V6 EGR Valve | RockAuto

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Discussion Starter · #7 ·
On the valve cover gaskets and valve adjustments: I have reused mine(gaskets) without a problem. However, be very careful when tightening the valve cover bolts on the side nearest the firewall. Do not over tighten or you will likely twist one off. Easy to do since these are the hardest to get too. Similarly, when adjusting the valves, the cylinders nearest the firewall are the most difficult to adjust based on the room you have to work and the awkward angle you have to get in to adjust the valves. This side, and the conditions present, is why it took me 4 tries to get near perfect rather than do it right the first time. There are a few more details in some of my other posts.
Just finished my second round of valve adjustments. I took a look at some of your other posts but I'm wondering if you have more details on how to get the adjustment perfect. There was no noise from the valve train before I adjusted the valves, but when I went in there the exhausts were very tight and the intakes were a bit loose, as expected. In retrospect I perhaps should have just left the intakes alone. However, after my first adjustment there was a lot of noise from the valve train, so I went in and readjusted, making sure that a .229 mm feeler gauge fit in the intakes but not a .254, and that a .305 fit in the exhausts but not a .330. Now the valve train is a good bit quieter, but still has clear valve tapping and is noisier than before I did the adjustment. To me, it seems like no valve should be too loose based on the fact that the next size feeler gauge does not fit in, yet there's still the noise; do you have any thoughts on how I could remedy this issue?

On the bright side, the rough idle has gone away beautifully and I'm putting some miles on the car now to determine if the running rich codes will do the same.

Thank you for your continued help!
 
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