TopBack430

I have the dreaded P0171 and P0174. Through a lot of research there does not seem to be a simple fix. Where I could use help is with deciphering the live data from Blue Driver. Attached you will see pics of the data I captured. I have replaced the MAF sensor(with cheap carquest sensor)

Just started car

Accelerating at 2500 rpm’s

20min in to drive and cruising at 55mph
but the readings do not look normal to me. Should the MAF have such large readings in combination with the fuel trim?
2004 SC430 with 108,000 miles
Pic#1 is right after start and idling
Pic#2 is with RPMs around 2500
Pic#3 is 20 min in and cruising at 55mph

should I buy an OEM MAF sensor?

Bgw70

My first step would be to check all vacuum lines very carefully. Unless you already replaced them.
Every single 2002-2005 SC430 will have a vacuum line problem. Not so sure about the 2006-2010 models
also, check those connections

TopBack430

I greatly appreciate your help! I am only as good as videos and forums allow me to be. I had it in a shop over the weekend. They spray tested for vacuum leaks and didn’t find any. In looking at your pictures, I have a hose that I do not see in yours. See attached picture. This hose also has duct tape near the clamp. Could this add to enough air to throw a lean code? Do you know what this hose is so that I can get a new one?

thanks for your time

Bgw70

my pics are from a 2002 SC430…very few changes between yours and mine.
Looks like mine was not connected to anything and has a cap.
not sure but that line on yours may go to the Power Steering vacuum assist.

You just need to verify the simple stuff before you put more money into the problem. Go slow and look very carefully.

here are a couple of more pics, check these vacuum lines, they are also very common and can look okay but are broken or disconnected, especially the blue box hoses.

Wilson2000

The first thing I would try is replacing the MAF with an OEM part bought through a Lexus dealer. It doesn't make sense to buy aftermarket components for your critical systems, like the EFI system.

Bgw70

I just did some reading on those codes for Toyota and two different people reported they had a cracked intake gasket…
Did all of the vacuum lines look good?
did you confirm the plenum clamps to the throttle body were tight and installed correctly?

Wilson2000

Likely, the way an intake gasket cracks and leaks is if the manifold plenum was removed an replaced without a new gasket, perhaps during a starter replacement.

Had any work been done on you SC prior to the codes? Always look at the maintenance/repair history leading up to any new problems. It's easy to inadvertently create new issues while fixing others, or while doing routine maintenance.

SGB4570

If you look at the hose on yours you have circled, it does not go all the way... you can see a full air gap between the sides of the clamp!! I'm guessing that is why the tape is there in the first place.