My honda odyssey 2002 has all this codes p0300,p0301,p0302,p0303,p0304,p0305,p0306,pp0307. Pls, what shall i do first 'cause i spend too much for gas.

These numbers are OBD codes. They are misfire coding.
There is a youtube video to assist with troubleshooting.
Trouble shooting misfire Code P0300 P0301 P0302 P0303 P0304 P0305 P0306...

Good luck.
Semper Fi,
Z

Answered in another location. This is a misfire code for #2.
Here is a video to assist in trouble shooting.
Trouble shooting misfire Code P0300 P0301 P0302 P0303 P0304 P0305 P0306...
Semper Fi,
Z

Trouble shooting a misfire, Code P0300, P0301 ... - YouTube

? 23:39
www.youtube.com/watch?v=G_grIaTgdRI
Oct 26, 2013 - Uploaded by Robert DIY For the new play by play misfire video click here: ... Trouble shooting a misfire, Code P0300, P0301, P0302, P0303, P0304, P0305, P0306, ...

Replace the coil pack.

Try this site for misfire codes and their diagnosis:

P0308 OBD II Trouble Code

also here:

Trouble shooting misfire Code P0300 P0301 P0302 P0303 P0304 P0305 P0306...

and herea;

Title goes here

check the coil if coil is ok spark plug if there are ok may damage in emission valve or injectors code relate it to the problems are p0300 p0301 p0302 p0303 p0304 p0305 p0306 p0307 p0308

Have you had somebody clear the codes after you installed the parts.If not the codes have to be erased by using a scan tool.

P0301 Cylinder No. 1 Misfire Detected
P0302 Cylinder No. 2 Misfire Detected
P0303 Cylinder No. 3 Misfire Detected
P0304 Cylinder No. 4 Misfire Detected
P0305 Cylinder No. 5 Misfire Detected
P0306 Cylinder No. 6 Misfire Detected
P1346 Variable Valve Timing (VVT) Circuit Range/Performance Fault
P1349 Variable Valve Timing (VVT) System Malfunction
P0330 Knock Sensor
P0446 EVAP Vent Control Fault
P0430 Catalyst System

Stop driving immediately.....

You defiantly skipped on your timing........

You need to have the ecm scanned for codes. The VSC and TRAC OFF lights are one just because the Check engine light is on. Once you clear the code in the ecm they will go off too.

p0456: evap system. sensor failure
p0172: evap system. intake blocked
p0778: exaust valve control. solenoid/ecu faukt
p0300: cylinders misfire. check ht/ignition leads
p0301,303,304,305,306: same ht leads

hope this helps..