Hi Scotty, Suzuki Grand Vitara I (2001 year) 1.6i Engine is idling at 900-1000 RPM. I accelerate to…

death

Hi Scotty,
Suzuki Grand Vitara I (2001 year) 1.6i
Engine is idling at 900-1000 RPM.
I accelerate to 1400-1500 RPM, then engine get drop to 800-900 RPM, but i don't release accelerate. After add more accelerate, then RPM will go upper and will not go down. Why is that? Also i have check engine code for air flow MAF sensor.
Can this sensor cause drop RPM when i accelerate just a little?
I have methane without injection. Same dropping RPM when i reach 1400 RPM.
Sometimes engine is idling at 500-600 RPM. Sometime when turn on engine, RPM will go down fast and off after i start it.
Cables looks fine, spark plugs is in good condition. No black color. Only white.
In highter RPM, engine is good.