I have a 2000 Lexus GS300 with the 2jz-ge. As most teenage boys are, I want my car to be fast, so I put a turbo kit in it.

I finished just a little bit ago, and my afr gauge is reading lean, and I don’t mean a little bit lean, I mean in the 20s lean. My car sounds like it’s got big cams while it’s idling, because of how bad the idle is.

I welded o2 sensor bungs into the down pipe, and there are not spacers on the o2 senators. I went from headers with cats to a down pipe with no cats, but I don’t think this should cause an issue with the afr running terrible lean.

Is it possible that my afr gauge is reading wrong? I don’t even know how the engine would run if it was that lean, especially at idle. There didn’t seem to be any misfires either when I drove it for the very short time I did.

Is it also possible that I have an exhaust leak or a vacuum leak? The down pipe doesn’t have a gasket or screw or anything, it’s one of the v-band clamp ones, and it is definitely more likely to leak than a screw in one. I did add some vacuum line T-sections so I can run to my BOV and to my boost gauge. I also don’t know where to connect the hoses that were connected to the stock air box, I think they are just breather lines but could they make a big difference?

The MAF is in the intercooler piping as well, so it should measure the amount of air coming in and have the engine adjust somewhat accordingly. I am on a stock ecu and injectors, which yes I know I need a tune, but I’ve seen many people online go na-t just fine with stock ecu and injectors and such. But it seems like my engine isn’t adjusting at all, it was running very lean

I almost feel like there is an exhaust leak, so my afr is reading super lean, and my car is running lean, but I feel like my afr is reading much higher than it actually is.

something else I’ve considered is a faulty MAF sensor reading

Do any of you guys have any ideas of what it could possibly be?

 

My car idles like its factory. NA-T with the factory ecu atm. It also enriches fuel to 11/10 depending on load and boost. I cut my maf housing from the air box and use couplers after cutting a section of the ic piping for it. Id say your maf housing might be 2 big for it to measure correctly. Either that or a vaccum leak some where. I also have a 340 pump and have spacers on 2 second stream O2's.

 

okay so here’s where I am at. I was tinkering with the restrictions in the MAF piping like you were saying how it’s smaller, and it seemed to make a huge difference, but not enough to fix my problems. My afr is still wild. Could a leaky midpipe and Unspaced o2 sensors be the root of my entire problem?