2006 lexus gs300 3.0L thats been non- op. For 4 months . it will crank but wont start. Ive added , new plugs. New gas cap .,a new MAF sensort cleaned the throttle body and still....no start. ,

Clean the MAF sensor and the throttle body. Plus the Idle air control motor. Use a toothbrush with brake clean. Just spray the MAF with brake clean both ways..

Have you monitored the engine sensors when this happens, if not have that done.

If the car sat, would bet all the money in my pockets that it's bad gas. Adding fresh gas won't solve the problem. You need to add a fuel stabilizer ( purchased for under $10 at Autozone) that you just add directly to the tank.
It could also be the case that the coil wires are dry and cracked from sitting, cause sparks to ground out.

Whenever your car won't start it is always one of three things-- fuel, spark or air. I hear you saying fuel is coming in, but to be sure you could try spraying a quick spray of carb cleaner or better yet starter fluid into the air intake and see if it briefly starts. If it does, then shuts down immediately, it's a fuel issue.

If not, then it is likely spark (air is usually not restricted but you may as well check the air filter and throttle body and make sure they aren't clogged. )

Check the spark in each cylinder. The problem could be a bad coil or fouled plugs.

If fuel, air and spark all check out, then the problem could be timing but this is highly unlikely.

ok , the cap fuel is not the problem , i think the problem is in key switch, try with spare or second key, .

revise primero que la llave este en buenas condiciones, pruebe con una de las copias, segun lei el problema esta en el cilindro de la llave, con la tapa de combustible mala lo unico que hace es encender la luz de check pero no impide funcionamiento eso es falso , suerte !!!!

Inside the intake manifold.

do you have spark? have you checked any of your sensors like crank sensor or cam sensor you said you small fuel I would do a fuel pressure test, befor you put a fuel pump in. please let me know if this helped i could have you do few more tests if needed

stockam auto

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Loose battery cable at the starter end, or sensor trouble, tighten cables, see if this helps, usually does, I get 50.00 per hour to check this, I render this 4 free 2 u.
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New Spark Plugs--every 70,000 miles
Clean MAF Sensor
New O2 Sensors--100,000 miles
Fuel Filter-every 3 years

Check TPS Sensor for opens

ok, i tell you 3 possible causes.
check maf sensor connection , check fuel pressure regulator (max press fuel in rail 40 psi) , check engine compression (min 95 psi ) if less this cause spark plugs wet and not start

check the pick up sensor