My Premio car with engine 1Az shows thise code p1820 how do I diagonise thise

Question edited for clarity.

Yes that is the error code

https://www.google.com/search?q=Toyota+caldina+1az+code+1235

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Might be a misfire.

you can try out some guide from here reliable-store
they also provide live chat feature for instant help and it's very useful

Google the codes

Problem with 2001 Toyota 4Runner? right? USA CAR?????
what engine, what displacement, how many cylinders?
gasoline or diesel???????????

p1820 (P1 is a toyota only factory code so don't read about fords etc)

the FSM covers all that ,as does alldata.com
how it works is complex, as are the monitors.

did you pull that code with your tools or Autozoned."?
what tool?

my listing ends at 1780. (a bad source, i guess)
2 car pros same answer.
i cant find it , but do answer all questions in bold please.

buy carb cleaner.,. remove the tube or hose going to the throtle,, .remember do not unplug any socket or wire sensor from d engine
start engine . then spray the carb cleaner direct at the throtle ..as the engine runing,d more u spray d more u have u rev d engine,,. rev the accelerator to 3 to 5000 Rms'tachomrter.. to flash out dirty carbon that causes the car to stop
do it several times,until u hear the engine is stable.and respond quickly..den stop eng, installed back d remove parts

SHOP MANUALS HAVE ELECTRICAL SCHEMATICS SHOWING ALL WIRING, COLORS, TRACER WIRES ETC.....VERY FEW PEOPLE COULD RATTLE OFF WINDOW REGULATOR COLORS OFF THE TOP OF THERE HEADS

The problem is with your air flow meter , you need to replace it

Yes.
D-4 is the type of fuel injection - direct injection.
vvt-i : Variable valve timing with intelligence.
It is used on Toyota's 2.0L first generation AZ engine family : 1AZ-FSE
1 - First gen
AZ - engine family
F - Economy narrow-angle valve DOHC
SE - Direct injection
Vehicles using the engine include Avensis, RAV-4, Premio, Wish and Allion

Code P0108 means your MAP sensor circuit is open. MAP means Manifold Absolute Pressure. You should be able to buy one at your local parts store - otherwise, the dealer.