2001 isuzu trooper hesitationg on acceleration around 30mph. could it be a mass air sensor problem? bad gas? just filled up the tank on friday, just started this morning. runs just fine until i rev the engine, slightly, rpms go up just as needed.

Try poking around in this forum. http://www.itocuk.co.uk/

Generally speaking for any vehicle. Check your air filter. It may be clogged. There is also a special spray for cleaning mass air flow sensors, like a carburetor cleaner spray. You loosen a hose clamp in front of the sensor and clean off the fine wire grill by spraying only. Don't touch. If you can see it from the air filter holder just blast down the tube. Let the gas evaporate a couple of minutes before you restart. The wires are delicate and need contact with the air to get a good reading.
You could also check the wires going into it. A blast of contact cleaner in a connector has cleared codes for me in the past, especially if leaking oil is blowing up. That is, if the filter and the sensor are clean.

If your mechanics say the mass air flow sensor, fuel pump and fuel filter is good then check your intake Manifold Gasket. It is a hard 1/4 inch thick plastic gasket that cracks frequently and causes sputtering when letting off your gas pedal and eventually lead to stalling at red lights and stop signs if cracked bad enough.

you either have a plugged fuel filter, a plugged converter or a bad mass air flow sensor

P0101 ISUZU - Mass Air Flow Circuit Performancehttp://engine-codes.com/p0101_isuzu.htmlForum CodePossible causes- Dirty mass air flow sensor
- Dirty mass air filter
- Mass air flow sensor harness is open or shorted
- Mass air flow sensor electrical circuit poor connection
- Intake air leaks
- Faulty mass air flow sensor
Tech notes Before replacing the mass air flow sensor, try replacing the air filter and cleaning the air flow sensor with low compress air or mass air flow sensor cleaner. Reset code and drive vehicle. If the code comes back, it may be necessary to replaced the mass air flow sensor

Mass air flow sensor error. Try spraying the sensor with mass air flow sensor cleaner(AND ONLY MAF CLEANER) and see if it clears up. if not you may be looking into a new mass air flow sensor. It should be located in the tube that goes to the air filter box.

if the vehicle has a mass air flow sensor it may be dirty remove and clean the mass air flow sensor with carb cleaner and it should take care of this.

If it was mine I would get as much of the old fuel out of the tank as I could.(syphon or look at tank for a drain plug)Change the fuel filter.Fill it with fresh fuel.Add a bottle of (Red color) STP fuel treatment.This will help remove condensation form the tank.Also check the condition of the air filter and install a fresh set of spark plugs,properly gaped.
The octaine in you old gas gets weak. Its not good to let it sit for so long.
I hope this helps you.

Check the Idle accelerator valve located on front side of throttle body, it is either stuck or needs cleaning real bad, this is what controls your idle speed, by letting small amount of air in. It has a plunger on it that moves back and forth slowly to adjust amount of air mixture, it is controlled by computer. Unplug it and just turn on key and check for voltage.This valve gets real gummed up, probably need to take apart throttle body and clean. HUNT

The metal pipes out from the tank rust drop it down and you will see the holes or put fuel hose right over them .

OK,,,GIMME ENGINE SPECS....AUTO...MANUAL...4WHEEL DR. 6CY...3.1...ETC......PLEASE