p0172 & p0174 (lean and rich) LSV8

[chandler1981]

Hey guys,

I am new here and tried to search but after several days of looking I broke down and decided to start this thread. I am working on a 2001 LS v8 w/ 150k miles with the DTC's p0172 & p0174. I am stumped as to what would cause one bank lean and the other bank rich?

I have recently replaced the all plugs and coils b/c of p0302 & p0304 and the vehicle has a very rough idle. It is most noticeable in gear while sitting still. It isn't throwing any misfire codes since replacing plugs and coils, only 172 & 174. One other thing is that occasionally, instead of idling rough it will idle VERY high when cold; like 2500 rpm's. I have checked for vacuum leaks.

The fuel pressure is around 38 psi KOEO. When KOER the pressure fluctuates between 35-40 psi at idle. A friend of mine purchased this vehicle at an auction (he's a dealer) so I would suspect that somebody has tried to fix it previously b/c I noticed one coil was replaced before i serviced it for him and many harnesses, wires, etc. have been messed with. One injector clip is broke but they are all snug on the injectors. I also noticed the TPS looks new but it does have the correct part number, per carquest. I swapped the bank 1 & 2 HO2 sensors around trying to see if the rich / lean banks swap but nothing yet..

Lastly, while idling VERY high the damn lower radiator hose BLEW OFF of the thermostat housing! (luckily I was checking the temp gauge at the time; it was 3/4 on the needle... pretty hot for only idling for a couple mins!) It didn't bust the hose or anything! The clamp and hose blew off together. I also noticed the degas bottle boiling over. (the cap was on.) It was running for a max of 2 mins when this happened from a cold start. So, do ya'll think this happened b/c the thermostat is stuck closed? I bled the cooling system several times prior to this happening as well.

After messing with the car for a few days (but before the boiling water incident) I called him and asked him if there was anything else he should tell me besides the rough idle. He replied, oh yea i had to add a good bit of water to it; it was dry.. I bled the system.. He also informed me that he cleared the codes (5 of them) that would be very helpful to me but he doesnt remember them and I can't duplicate them. I am willing to bet it was due to the overheating. (Maybe p1299 along with the 172, 174, and 302&304 that have cleared since replacing plugs and coils is my guess) ?

Sorry for so long of a post. Hope I didn't leave anything out!

In summary... What causes p0172 & p0174 together? intake gasket?
What caused the hose & clamp to blow off the thermostat housing?
I am going to test the coolant for carbon monoxide to look for head gasket problem once I am SURE that hose doesn't blow off again!

Any help or other ideas would be greatly appreciated.

 

[chandler1981]

Ok, I replaced the hose along with a new clamp and also bought a new thermostat just incase it was stuck. I'm thinking it was ok tho.

When I started it this time, it idles at 2-3000 rps and if i touch the throttle, it idles up even more and will even hit the rev limiter. It won't idle back down; I have to turn it off... Any ideas?

 

[joegr]

Is the engine smooth at highway speeds, or a little rough?
Does it seem to have full power?
I've seen that combination of codes before when one of the cams is out of time due to failure of a timing chain tensioner.

 

[tireman]

vacuum leak

You're riding in a 2001? PVC valve and hoses! Another thing for idle problems is the IAC valve.

 

[joegr]

You're riding in a 2001? PVC valve and hoses!

The V8 has no PCV valve. I don't think that the PCV hoses on the v8 suffer from failure much as they are small and thick walled.

Never the less, a vacuum leak would be one of the things to look for.

 

[chandler1981]

Hey, Joegr. Thanks for the replies man. It runs extremely smooth at highway speeds. Actually, it runs smooth at all speeds. It just has a rough/erratic idle. It almost feels like a misfire when sitting still. The idle is more noticeable or worse when car is in drive or reverse. I'm assuming maybe b/c of the load difference between in gear and park. When sitting still and trans in drive or reverse, you can feel the "misfire" and it actually surges a little bit. Once you press the throttle everything is normal. DTC's are always stored during idle as well. Freeze Frame always shows the DTC stored around 750-825 rpms. Coolant temp is usually around 190-210 when DTC is stored IIRC. Engine power is normal as well.

My problem now is that the idle is around 2000-2500 rpms. It started doing this after I attempted to clean the IAC... If i press the throttle while it is idling high it revs even higher (around 2600-2800 rpms) and takes a long time to return to 2000 rpms. I am thinking the IAC is bad but i can't figure out if the rough idle/surge is another issue that is being overshadowed by the high idling for now... Thanks again.

What is the round stainless thing that is on the fuel supply line right over the drivers valve cover? Is this factory? It goes from a metal line (right below the evap service port), to a hardened fuel hose, then the "Stainless thing" then another hose coming off of that to the fuel rail. Is it normal for the fuel pressure to fluctuate 3-5 psi constantly while idling? I think it was fluctuating between 35-40 psi.

 

[chandler1981]

Thanks joegr for the replies. Yes is runs very smooth at any speed. It only has the issue during idle. It appears to be worse while in gear sitting still. I guess its b/c of the load. It has normal power too. It surges while in gear and sitting still.

The issue now is that it is idling at 2000-2500 rpms and if i press the throttle it revs even higher and SLOWLY returns to 2000 rpms. This seemed to begin shortly after I cleaned the IAC.

Also, should the fuel pressure fluctuate 3-5 psi while idling. What is the stainless thing that comes off of the metal fuel supply line near the drivers side valve cover? Under the evap service port the supply line goes from metal line to hardened rubber line, then into the round stainless thing (maybe a regulator), then back into a hardened rubber hose and then into the fuel rail. Is this factory?

Thanks again. I am wandering if the IAC is bad but I also think the rough idle/surge that was happening is another issue and is overshadowed by the high idle I have now.. Thoughts?

 

[joegr]

Thanks joegr for the replies. Yes is runs very smooth at any speed. It only has the issue during idle. It appears to be worse while in gear sitting still. I guess its b/c of the load. It has normal power too. It surges while in gear and sitting still.

The issue now is that it is idling at 2000-2500 rpms and if i press the throttle it revs even higher and SLOWLY returns to 2000 rpms. This seemed to begin shortly after I cleaned the IAC.

Also, should the fuel pressure fluctuate 3-5 psi while idling. What is the stainless thing that comes off of the metal fuel supply line near the drivers side valve cover? Under the evap service port the supply line goes from metal line to hardened rubber line, then into the round stainless thing (maybe a regulator), then back into a hardened rubber hose and then into the fuel rail. Is this factory?

Thanks again. I am wandering if the IAC is bad but I also think the rough idle/surge that was happening is another issue and is overshadowed by the high idle I have now.. Thoughts?

I think it could all be the IAC. The fuel pressure will vary with intake manifold vacuum level. If the IAC is bad and constantly opening and closing, then you will get manifold vacuum fluctuations. You could test by disconnecting the electrical connector to the IAC. You will have to keep you foot on the gas pedal to keep it running. If that resolves the high idle and the variations, then the IAC (aka Idle Air Bypass Valve) would be a good candidate for replacement.

 

[chandler1981]

Thanks again joegr. I will report back shortly. Any idea what the thing is I mentioned in my previous post that runs inline on the fuel supply line near the fuel rail?

 

[joegr]

Thanks again joegr. I will report back shortly. Any idea what the thing is I mentioned in my previous post that runs inline on the fuel supply line near the fuel rail?

Could you post a picture? I'm not always good with word descriptions...

 

[chandler1981]

ok, so I replaced the IAC and the idle is at normal rpm. Now my problem is that the "surge / stumble" still exists at idle. I tried to test for combustion gasses in radiator but cant run the car with the degas bottle cap off. I drained a good bit of coolant and it still backflows into the tank and boils or bubbles out of the tank. I seem to think it has a blown head gasket. Another issue is that I have spent 2 days getting air out of cooling system and it appears to be no better than when I began. This leads me to believe that it is a head gasket issue b/c it is continuing to spew coolant and air out no matter how many times I bleed it. Thoughts? The P0174 came back immediately after replacing IAC and the p0172 came back shortly afterwards. I think the 174 set off the 172 but I can't figure out what is causing the cooling system to bubble so much that I cant even test for carbon monoxide in reservoir. Could a lower intake leak cause all of this? Thanks to anyone who can help!

 

[joegr]

Yeah, that does sound like head gasket. Sorry...

 

[chandler1981]

UPDATE:

Radiator cap was bad, coolant fill cap was cracked on the inside threads, and the only code now is to P0174. (Lean Bank2)

I changed the fuel filter and the "filter" side (coming from tank) was black! the fuel that was filtered wasn't dirty though. Anyway, I got some fuel trims for ya to look at..

Before replacing fuel filter...

P0174 (Lean Bank 2)

Load 45.4%
Coolant Temp. 195 deg F
stft 1 0.0 %
ltft 1 -13.3%

stft 2 13.2%
ltft 2 23.4%

stft 3 -38.3%
ltft 3 57.0%

stft 4 17.1%
ltft 4 26.5%

Vehicle speed 0 mph
Fuel System 1 - CLSD
Fuel System 2 N/A

These are after filter change... still p0174

Rpm 748
Load Value 26.2%
Temp 197 deg F

STFT1 1.0%
LTFT1 -25.6%

SHFT2 12.5%
LTFT2 24.2%

SHFT3 17.1%
LTFT3 -11.6%

STFT4 8.5%
LTFT4 49.2%

Veh speed 0 mph
Fuel sys 1 CLSD
Fuel sys 2 N/A

Any ideas... I still expect a blown head gasket... But just checking to see if anybody can sipher through this japanese shyt!! Thanks for your help!