Engine misfiring

When all cylinders misfire. It the air mass sensor that doesn't detect air coming in the engine cause misfire. Not enuff oxygen. It doesn't happen at all like that. Give a try to replace air filter, pcv valve need to be replaced and air mass sensor replaced and use obd2 scanner to erase code and see what happen. It wouldn't come back on

Had check engine light come on auto zone diagnosis was misfire cylinder 1 &6 and random misfire have replaced plugs wires all coil packs and #6 injector still surges and runs poor any idea

I have a 2000 Toyota Sienna XLE which is having some problems. The engine seems to be misfiring and the codes P0300 P0304 P0306

I replaced the plugs and the fuel filter so far. Should I replace the plug wires next? It seems like they will be hard to change at the back side near the firewall. Any suggestions would be helpful. Thanks

You should replace the spark plug wires when you replace the spark plugs. Do you know if the intake plentum must be removed to replace the wires by the firewall?

I had the water pump, timing belt and seals replaced around 91, 00. I do regular oil changes, and have noticed some oil drops on floor over last year(though oil level is always fine).

Car was driving fine till yesterday. Today wife complained (after driving five miles) about burning smell and steering wheel was vibrating. Check engine lights came on.

I checked codes - P0300, P0302, P0305. I found the coolant tank was almost empty(some coolant at bottom). I found the engine compartment was sprayed with white salt type liquid and dried (I have photos).

I reset codes. Refilled coolant. I started the engine after refilling coolant it runs fine, but the steering wheel vibrates when engine is in "D". Also the panel light for "D" does not illuminate (P and R lights do illuminate).

Need help to figure out if it is a radiator issue or spark plug/coil issue. I also have some oil leaking from the engine that was already present due to age of the car.

Thanks HMAC300. I will try to get the system pressure tested today.
Some more information. I started the car and got it to operating temperature. The codes returned (P0300, P0302, P0305). No visible leak except for a few drop of coolant dripping below radiator. The engine and steering wheel vibrates when put in gear(R/D) but not in P or N. I touched the inlet and outlet radiator hoses both are hot with car just parked in garage. Sounds like radiator issue?

I am going to do coil swap to rule our coils/wires. Will put in the fuel injector cleaner to clear nozzles.

Any other suggestions?

Pressure tested using Harbor Feight Radiator Compression Tester. Radiator has a leak at top inlet pipe. Coil swapping to be done next.

Thanks all for the help. After researching and getting help from posters like you, I was able to sort out the problem (hopefully.)
1. Problem#1 Busted radiator - Radiator inlet was leaking as detected using the pressure test. Replaced with new radiator. Drained/flushed/refilled coolant.
2. Problem#2 Engine Misfire cyl #2 & 5. Turned out to be bad ignition coil. It was my mistake earlier to have not labelled the coils properly when swapping. When I did the spark test - it came out clear.
3. Problem #3 Exhaust manifold(Upper catalytic converter) was turning red hot due to unburnt fuel getting there. This was due to Problem #2 and so once that was fixed, it corrected.

I learnt a lot in the process and am thankful to the community for tips. Youtube is also great help.

Misfire #1 cylender. During ideal and acceleration. Comes and goes. Might be weather related misfire less during cooler low humidity days. Temperature under 70 degrees less misfire occurrence.

Forgot to mention Scan error codes P0300 & P0301. I know P0300 is random misfire & 301 is misfire cyl#1.
It acts more like an occasional bad connection. ("On again/off again" misfire)
If it was fuel pressure problem would it only affect one cylinder? And if it did, would it then be a injector problem?

Will do, will report back, Thanks!