This hose is ripped in the area circled (hard to see the rip in the picture), and the other end (not pictured) seems to have come off completely. Can anyone tell me what this hose is called, and ideally give a part number? Also, what does it connects to at the other end?

Several days ago, I got the "check engine" and "VSC Off" lights with the codes P0171 and P0174. The short-term and long-term fuel trims are extremely high on both banks (over 30% LTFT and around 10% STFT). I removed the engine cover today and noticed this tear. I tried to find the other end, but the hose came out completely. (Either it was barely hanging on and I pulled it all the way off, or it was already all of the way off.)

Is this hose being completely disconnected likely to be causing the lean mixture error?

 

The hose connects to the ACV (air control valve) which is a power steering component. Some people call it the idle up valve.
There are 2 hoses connecting to the ACV. The hose you’ve circled is 1734350141. It’s sister hose is 1734250160.

If it’s disconnected or broken unmetered air is flowing freely into the intake.

 

Great, thanks. Does it matter which of the two hoses is connected to which nipple on the ACV?

 

No it doesn’t matter.

 

Thanks. Is there a recommended procedure for installation? I’m finding that access to the ACV is a bit difficult — I’m not totally confident that my hoses are seated properly.

 

If you’re reporting back this quickly I’m guessing you chose generic auto part store hose.
I don’t blame you the genuine Toyota hoses are pricey!
Unfortunately this is likely the issue. The hoses you are replacing have an ID measured in MM and the parts store hose is imperial.
What size hose did you buy? Have you removed the air filter box for access?

 

I actually am just reattaching the existing hose to see if the fuel trim is at least improved. I ordered the OEM hose but won’t have it until next week.

I did remove the air filter box but my hands are a bit too big to hold the end of the hose (close to the ACV). I’m guiding the hose onto the nipples with my hands placed about a foot away from the end. (And obviously I cannot seat the flexible metal clamps at this distance.)

Short term fuel trim is now reduced to under 10% but long term fuel trim is still nearly 30%. Do I need to reset the ECU in order for LTFT to reevaluate, or does it happen over time as I drive?

Also, is there potential damage if I drive in this condition, or does it just hurt MPG?

 

The ACV's function is to provide smoother steering response when the PS pump is under load like when you're cranking the wheel in a parking situation.
If you're just testing for the sake of MPG you can temporarily plug both ports up top. Just don't leave it that way...

 

Interesting. So if I plug this up, then I should temporarily solve the fuel trim problem, too, correct? I just will have the VSC Off light?

 

I can't say for sure what will happen with the VSC light. It's triggered by a variety of things many of which are inconsequential to everyday driving.
When the PS pump is under load it pushes a tiny piston inside the valve which gradually opens a valve. This allows air to move through the intake and throttle body.
The additional air raises RPM's which spins the PS pulley faster. The faster the pump spins more fluid (hydraulic power) moves through the PS system.
Like I said, you can completely disable it's function just don't leave the ACV down there with no hoses attached for an extended period of time.
I removed (plugged) the ACV on my 400 because it was leaking and couldn't feel any difference in steering at all.

 

It kind of surprises me that they still used the P/S idle up valve on these, as I figured they would have been phased out in the 90s!

As others have said l, it's okay to leave it disconnected for now, and ensure that the hose ends are plugged. It's common for many people in the Toyota/Lexus community to remove the valves once they start to leak internally, and then screw some sort of a bolt of the same size into where the valve was to plug the hole on the pump.

 

Thanks, guys. I reattached the two hoses, though the ripped hose does not seat properly on the engine intake port. (The other hose, which connects to the air filter box, is fine.) Fuel trims improved and the steering was noticeably better. The fuel trim at idle was still too high (30% for STFT) and after a while the Check Engine and VSC Off lights came on again. MPG are very low (~14MPG).

Until the hose arrives, should I plug BOTH the port attached to the engine, AND the ACV? Or just plug the engine port and leave the one ACV port open with nothing attached?

 

Having similar issues. Anyone able to confirm what the fix could be?

 

Have neither one of you cleaned the MAF sensor?

There are many diy videos on the web showing you how to clean the MAF. See attached jpg

Make sure to clean the intake air temp sensor and the two thermistors/resistors, see the arrows

 

Just had a chance to clean my MAF. There was something attached to the one of the resistors in the picture above. Sprayed MAF cleaner and it removed it. Also unplugged my battery for 20 mins to allow everything to reset. Drives a lot better and responsive. Will report back after a few trips.