I am having a random problem on my toyota rav4 2003. When I come to a complete stop, it is very hard sometime to switch from the first to the second and the second to third gear. But on third gear, it runs fine. But it does not happen every time.

run the fault codes
indicates possible crank/ cam shaft position sensor/s faulty

There could be multiple issues here and it's hard to say without really looking/running numbers - is there power (lights/dash symbols/etc) when you turn the key? Or completely dead?

If completely dead, did you see a random brake light while driving? That could indicate a bad alternator. Does jumping it start her? If so, possible you have a parasitic draw in the system draining the battery.

Ground wires are important to check, also.

Off hand, without much data to work with, mass air flow sensors can cause a no start - try unplugging this and starting. You can also backprobe to test sensor and harness for ground. This may not throw a code right away.

I see "sometime," so if assuming a start at times and others not randomly - recheck ignition switch assembly wires, follow them and see if any are loose. A friend had this issue and found the ignition switch assembly wire coming from the alarm was loose.

No codes and random starting, I'd lean wiring. Maybe retrace your steps - it sounds like you tackled the more indicative issues already.

Get the hood switch checked. Have seen this problem several times.

hi there . think they may need a bit of wd40. spraying on the shaft.
probably just road dust and debris. making it stick.

you might of press it to hard when that happens just touch the switch the opposite way,sometime the switch get stuck

TRY THIS. REMOVE THE INTAKE ON THE RIGHT SIDE OF THE CAR .THE EGR VALVE CLOGS UP WITH CARBON SOMETIMES CHOKING IT OFF COMPLETELY. IT WILL BE HARD TO START WHEN THIS IS CLOGGED. CHUNK OUT THE CARBON WHERE THE BUILD UP IS. REPLACE WITH A NEW EGR.

if you have alot things on keychain ignition could be going bad. shake switch when it happens. sometimes remove weight from keys can stop it

I have the same problem. I have had it in the shop on numerous occasions and they couldn't find the problem. Yesterday it stopped working altogether. I'm stuck in 2WD and there is a snow storm arriving tonight.

Horns have constant power all the time so when you press the horn button, all you are doing is grounding the circuit and that makes the horn blow. Usually what happens is that a spring breaks underneath where the horn button is or something allows the horn button to ground out somewhere, possibly even through the inside of the steering column.

Sounds like the voltage regulator is starting to fail. Your voltage regulator is built in to the alternator, so you should replace your alternator before it dies completely and leaves you stranded somewhere.