LTFT and STFT connection to PCV valve and intake manifold gasket

I have a 2011 Rav4 4cyl with 130k mikes and last year I replaced the A/F ratio sensor. 3 weeks ago I had some issues with rough idle due to a lose vacuum hose which I knocked out when replacing the air filter. A month ago since then I keep my lil $30 scanner hooked to the ObD whenever I drive and monitor STFT and LTFT. My LTFt were around 7-8% when crusing at 75mph and they would not come down or change fast enough so i decided to replace the downstream O2 sensor after which the readings LTFT readings were lower and would change with speed etc but they still were at 7% when cruising at 75mph. I then ran into a video which said I should replace my PCV valve which I did but. Put thread locked instead of three sealant and I could hear a hissing sound which bumped my LTFT to a max of 8.6 and my STFT max of 2.3%. While doing thr PCV valve I realized the intake gasket was leaking so I decided to do replace new intake gasket and also got my fuel injectors professionally cleaned from a local guy here. I replaced the intake manifold gasket put thread sealant on the threads of the pCv valve as thread locker is not adequate to make a seal, replaced the hose between the vacuum switching valve and the PCV valve as that’s what the FSM says and put the system back together and engine response, acceleration has improved significantly . I think the gas mileage has gone up a lil as well but my fuel trim numbers are identical to what they were prior to doing all this work. Now at 75 mph my STFT bounces between 0,0.8,1.6 and LTFT is at 7-7.8% when cruising at 75mph. I have Observed as the ltft drops the gas mileage goes up I was hoping for a lower ltft after all the work I did. While replacing the intake manifold gasket I had to pull out the hose that connects the brake booster to the VSV. One of the hoses has cracks at the end but not where it clamps to a metal hose. Should I replace it or if yes will it make a difference. Another thing is the air box when I clamp it after putting the air filter in is not very tight would that result in more air being sucked in and the maf telling the ecm to increase fuel supply as more air is being pumped in. My aim is to bring LTFT as close as possible to 0 or perhaps lower it when cruising as that in my observation delivers better fuel economy. My other question is does the PCV valve have an effect on ltft or STFT. If I pinched the PCV valve hose the engine would not idle well. I am going to look for more vacuum leaks and replacing intake gasket improved braking and acceleration. Any or help and explanations will be appreciated . Thanks

Hey Radhe! Before trying to answer your questions, I'm gonna say that you might never get your long term trims to zero. I understand the desire to get closer to zero correction, and the improved fuel economy. But no fuel control system is perfect. :silly: The engine computer can't control everything (fuel quality, mechanical wear, carbon deposits, like that), and that's what the trims are for. There's always gonna be some correction.

BUT, if you're dead set on making improvements, then more power to you!

Radhe wrote:

One of the hoses has cracks at the end but not where it clamps to a metal hose. Should I replace it or if yes will it make a difference.

The hose from the brake booster to the intake? It's likely making *a* difference, but it may or may not be something you'd see in the fuel trims. As long as the area of the hose that's clamped to the metal barb is intact, you likely won't see a big improvement by replacing the hose. But hey, if the hose is cheap and readily available, why not try it?

Another thing is the air box when I clamp it after putting the air filter in is not very tight would that result in more air being sucked in and the maf telling the ecm to increase fuel supply as more air is being pumped in.

The simple answer is no, I do not believe a slightly leaky air filter seal would increase fuel delivery.

Correct me if I'm wrong, but I think what you're really asking is, could this cause an increase in fuel trims? Simple answer is also no. In your case, the air coming into the engine is mostly coming through the air filter, with some (probably not much) coming past the air filter seal. The combined air mass is getting measured by the MAF, and the corresponding amount of fuel gets injected. Since there's no discrepancy between the actual amount of air coming in and the amount the MAF measured, there's no problem.

Long answer is that air leaks ahead of the MAF can screw with the laminar flow of air past the MAF, resulting in incorrect measurement. It's pretty rare, in my experience, but it happens. How do you know if that's happening on your car? A quick and dirty test would be to get your car fully warmed up, turn all accessories/loads off, in Neutral/Park, and observe the MAF g/s reading. It should be 100-115% of your engine displacement in liters. Assuming you have the 2.4L 2AZ, the MAF should read 2.4 g/s or just above it.

My other question is does the PCV valve have an effect on ltft or STFT. If I pinched the PCV valve hose the engine would not idle well. I am going to look for more vacuum leaks and replacing intake gasket improved braking and acceleration. Any or help and explanations will be appreciated . Thanks

The PCV can definitely have an impact on trims. A PCV that's stuck open, or flowing more than intended, can result in higher trims at idle. That the idle changed when you pinched the hose isn't unusual, since you just changed the amount of air going into the engine. Is that hissing noise you mentioned still there?