FINALLY SOLVED! P0171 And P0174 Codes!!!! - ClubLexus
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Here we see: Numerous Vacuum Lines, Intake Manifold Gaskets, Plenum Gaskets, Valve Cover Gaskets, Spark Plugs, Injector Seals for all 6 Injectors (also cleaned injectors), EGR valve, Air intake control Valve gasket, Air filter, numeruos vacuum line clamps, Crush Washers for fuel rails, and a few other things. Now this pretty much had me at a loss because I replaced nearly EVERY COMPONENT that could possibly be a culprit to this issue. I am sure that Lexus Techs have tried or done the same thinking "this has to be all it can be". Well after tearing the engine apart and replacing all the above and servicing and cleaning the injectors and entire intake and throttle body, I was thinking that this will do the trick. I had my fuel pressure tested as well and it was fine (54lbs.). So I knew I didn't have a fuel suply issue from the tank. Put it back together and turned the key thinking problem solved. AND NO!!!!!!!!!! WTH MAN! I literally replaced everything. I even inspected the plastic manifld for cracks! Nothing. Still showed High Fuel Trim on the Long Term Side after engine warmed up! GRRRRRRRRRRRRRRRRRRRRRR!!!!!!!!!!! What the hell would be next???? I was lost. Went to dealership. Wrote a check for them to diagnose the problem. They did smoke test on system and found no leaks in the vacuum, and reset code and told me system would adjust after a few cycles blah blah blah. They even reset my ECU! ONE WEEK LATER......CODE P0171 and P0174!!!!! AGAIN At this point I had no clue what to do. Read and read and read about lean codes. Read some more. Inspected all vacuum lines again. Cleaned new maf just in case. Nothing. Then, FINALLY, AFTER nearly 8 months of fighting with this code KAAAAAAAABBBBBBOOOOOOOOOOMMMMM!!!!!!!! I FOUND THE ISSUE! And I discovered why Lexus techs and mechanics are lost at times. They know it was likely a leak in the vacuum system, but could never clearly identify what was leaking! I DID!!!!! While inspecting the engine yet again for potential leaks etc, I was running my hand along the left side of the intake manifold (black plastic) when I placed my hand and fingers and some weight against the AIR INTAKE VALVE on THE LEFT SIDE OF THE ENGINE INTAKE. Now the mechanism and linkage from the vacuum bladder that operates it had my fingers slightly pressing on it and I noticed an engine RPM change and a slight change in the pitch of what sounded like my engine beltpulleys making noise. I release and the engine returned to what is was and had been doing and sounding like. At this point I though to myself that maybe I had simply just moved the linkage enough to move the internal valve inside the intake manifold. So I again placed my fingers near the linage to the valve this time just barely placing enough pressure on the linkage to change the pitch of the noise, yet ensuring I did not MOVE THE VALVE inside. The pitch changed again and engine revs changed slightly. I immediately connected my scanner and drew the live data up. Did it again and pressed on the linkage and BAM THE FUEL TRIMS DROPPED TO NORMAL!!!!!!!!!!!! BOOOOOOM Maybe this was it!!!!! But how???? This was not a vacuum line, simply linage to the internal air valve. I tested the vacuum line going to the valve bladder (sucked and watched the valve mechaism move thus moving the internal valve and held it and it was air tight. What the hell. How could this be leaking if the bladder holds a vacuum and the linkage works and holds when there is a vacuum???? Well, what the hell, I've already replaced everything else, might as well replace this. TOYOTA PART NUMBER: 17320 0A010 Air Intake Control Valve No 2.Bought it. Tore the intake apart again to get the old one out. See photo:
The mechaism to the left my thumb in the photo is what I replaced. It is also picture above. Now when I removed the old one, I noticed some "play" in the SHAFT THAT RUNS FROM THE CONNECTING LINKAGE THROUGH THE PART THAT MOUNTS TO MANIFLD TO THE VALVE ITSELF. See the photo for a picture of the shaft. THIS IS WHERE THE LEAK WAS COMING FROM!!!!!!!!!!!!
THIS PHOTO is of the linkage WITHOUT PRESSING ON IT. This photo however....
Shows a slight gap in the shaft area. You CAN CLEARLY FEEL A LOT OF PLAY especially comparative to the new one. There are two rubber seals int he linkage that obviously have gotten old and began to leak due to the play. But why would the "leak" be intermittant and only throw a code on occasion..... BECAUSE THE VACUUM VALVE HAD TO BE WORKING TO EXPOSE THE PLAY IN THE SHAFT LINKAGE and this usually only actuates at idle at start up or idle while driving. IF YOU WERE NOT IDLEING THE CAR FOR LONG PERIODS, the leak is not apparent and thus the fuel trims are not HIGH ENOUGH FOR LONG ENOUGH to throw a code. At some point they will, but thus the intermittant code throwing!!!! I once reset my code and drove 237 Miles BEFORE THE CODE thre again! It was nearly ALL HIGHWAY MILES....DING DING DING. NO IDLE TIME thus no intense vacuum thus no code throwing. Now if a Lex Tech hooked up smoke machine, HE WON'T FIND THE LEAK AS THE VACUUM DRIVEN VALVE WILL NOT BE ACTUATED AND THUS THE LEAK NOT APPARENT AT THAT TIME. The rest of the system will check out and you will be back at sqaure one!!!! PLEASE PLEASE PLEASE Have your Mechanic check this valve mechanism if you are getting these codes. The leak is coming from the SHAFT THAT CONNECTS TO THE VALVE!!!!!!! After months and months and countless hours, I FINALLY DISCOVERED THE ISSUE!!!!!!!!!!


Email me at [email protected] with any questions. Last edited by Rainbird; Apr 25, 2015 at 04:52 PM. Reply
Here we see: Numerous Vacuum Lines, Intake Manifold Gaskets, Plenum Gaskets, Valve Cover Gaskets, Spark Plugs, Injector Seals for all 6 Injectors (also cleaned injectors), EGR valve, Air intake control Valve gasket, Air filter, numeruos vacuum line clamps, Crush Washers for fuel rails, and a few other things. Now this pretty much had me at a loss because I replaced nearly EVERY COMPONENT that could possibly be a culprit to this issue. I am sure that Lexus Techs have tried or done the same thinking "this has to be all it can be". Well after tearing the engine apart and replacing all the above and servicing and cleaning the injectors and entire intake and throttle body, I was thinking that this will do the trick. I had my fuel pressure tested as well and it was fine (54lbs.). So I knew I didn't have a fuel suply issue from the tank. Put it back together and turned the key thinking problem solved. AND NO!!!!!!!!!! WTH MAN! I literally replaced everything. I even inspected the plastic manifld for cracks! Nothing. Still showed High Fuel Trim on the Long Term Side after engine warmed up! GRRRRRRRRRRRRRRRRRRRRRR!!!!!!!!!!! What the hell would be next???? I was lost. Went to dealership. Wrote a check for them to diagnose the problem. They did smoke test on system and found no leaks in the vacuum, and reset code and told me system would adjust after a few cycles blah blah blah. They even reset my ECU! ONE WEEK LATER......CODE P0171 and P0174!!!!! AGAIN At this point I had no clue what to do. Read and read and read about lean codes. Read some more. Inspected all vacuum lines again. Cleaned new maf just in case. Nothing. Then, FINALLY, AFTER nearly 8 months of fighting with this code KAAAAAAAABBBBBBOOOOOOOOOOMMMMM!!!!!!!! I FOUND THE ISSUE! And I discovered why Lexus techs and mechanics are lost at times. They know it was likely a leak in the vacuum system, but could never clearly identify what was leaking! I DID!!!!! While inspecting the engine yet again for potential leaks etc, I was running my hand along the left side of the intake manifold (black plastic) when I placed my hand and fingers and some weight against the AIR INTAKE VALVE on THE LEFT SIDE OF THE ENGINE INTAKE. Now the mechanism and linkage from the vacuum bladder that operates it had my fingers slightly pressing on it and I noticed an engine RPM change and a slight change in the pitch of what sounded like my engine beltpulleys making noise. I release and the engine returned to what is was and had been doing and sounding like. At this point I though to myself that maybe I had simply just moved the linkage enough to move the internal valve inside the intake manifold. So I again placed my fingers near the linage to the valve this time just barely placing enough pressure on the linkage to change the pitch of the noise, yet ensuring I did not MOVE THE VALVE inside. The pitch changed again and engine revs changed slightly. I immediately connected my scanner and drew the live data up. Did it again and pressed on the linkage and BAM THE FUEL TRIMS DROPPED TO NORMAL!!!!!!!!!!!! BOOOOOOM Maybe this was it!!!!! But how???? This was not a vacuum line, simply linage to the internal air valve. I tested the vacuum line going to the valve bladder (sucked and watched the valve mechaism move thus moving the internal valve and held it and it was air tight. What the hell. How could this be leaking if the bladder holds a vacuum and the linkage works and holds when there is a vacuum???? Well, what the hell, I've already replaced everything else, might as well replace this. TOYOTA PART NUMBER: 17320 0A010 Air Intake Control Valve No 2.Bought it. Tore the intake apart again to get the old one out. See photo:
The mechaism to the left my thumb in the photo is what I replaced. It is also picture above. Now when I removed the old one, I noticed some "play" in the SHAFT THAT RUNS FROM THE CONNECTING LINKAGE THROUGH THE PART THAT MOUNTS TO MANIFLD TO THE VALVE ITSELF. See the photo for a picture of the shaft. THIS IS WHERE THE LEAK WAS COMING FROM!!!!!!!!!!!!
THIS PHOTO is of the linkage WITHOUT PRESSING ON IT. This photo however....
Shows a slight gap in the shaft area. You CAN CLEARLY FEEL A LOT OF PLAY especially comparative to the new one. There are two rubber seals int he linkage that obviously have gotten old and began to leak due to the play. But why would the "leak" be intermittant and only throw a code on occasion..... BECAUSE THE VACUUM VALVE HAD TO BE WORKING TO EXPOSE THE PLAY IN THE SHAFT LINKAGE and this usually only actuates at idle at start up or idle while driving. IF YOU WERE NOT IDLEING THE CAR FOR LONG PERIODS, the leak is not apparent and thus the fuel trims are not HIGH ENOUGH FOR LONG ENOUGH to throw a code. At some point they will, but thus the intermittant code throwing!!!! I once reset my code and drove 237 Miles BEFORE THE CODE thre again! It was nearly ALL HIGHWAY MILES....DING DING DING. NO IDLE TIME thus no intense vacuum thus no code throwing. Now if a Lex Tech hooked up smoke machine, HE WON'T FIND THE LEAK AS THE VACUUM DRIVEN VALVE WILL NOT BE ACTUATED AND THUS THE LEAK NOT APPARENT AT THAT TIME. The rest of the system will check out and you will be back at sqaure one!!!! PLEASE PLEASE PLEASE Have your Mechanic check this valve mechanism if you are getting these codes. The leak is coming from the SHAFT THAT CONNECTS TO THE VALVE!!!!!!! After months and months and countless hours, I FINALLY DISCOVERED THE ISSUE!!!!!!!!!!


Email me at [email protected] with any questions. Last edited by Rainbird; Apr 25, 2015 at 05:19 PM. Reply
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