clauddio09

Hello. I'm a first time user. I have a 2001 gs300 with misfires showing codes 300 and 306 and 305. the car does not show symptoms of misfiring although the CEL flashes sometimes when driving. so far I replaced the plugs, wires and coils with lexus parts. no change. the oil control valve was also replaced along with the filter. I'm out of ideas. yesterday I noticed a cat code showed up also...code 420. anybody had this problem before? any ideas as to what can be? other than just a little bit of hesitation sometimes when starting from a dead stop the car does not show any signs of misfiring. I'm done throwing parts at it. any replies much appreciated.

DriftOner

Is there any oil or coolant down in the plug valley? The heater hose at the back of my engine was leaking into the plug valley and caused misfires once.

Mcon

iTrader: (1)

Check this 2 hoses first. One is next to the other. If the hoses are okay and not any oil cover valve leak. Is your spark plugs wires # 5 with the coil on spark #6. P0300 Is general misfire. P0305 is spark 5 with coil 3 or spark 6 misfire. This the hoses and the location on the intake manifold after the throttle boby. I hope and this info and picture help you.







The clamp cove the crack on the hose and that make a air leak and code misfire.

clauddio09

thank you for the replies. when I changed the plugs and wires I noticed oil in the valley so I replaced the valve cover gaskets. I didn't see any coolant down there at that time...only oil..after that the car still triggered the check engine light with the misfiring codes. I checked today and it still looks nice and clean there. I will replace the hoses that you mentioned and take it for a test drive tomorrow. thank you. I will update later

clauddio09

I replaced the hoses and took the car for a test drive but the CEL came back on within minutes. This time all these codes came up...300..305..420 and 430 so i guess the cat converters are failing too...what I find bizarre is that the CEL flashes as if detecting a major misfiring issue but the car shows np symptoms at all...no rough idle or stumbling or loss of power....

Mcon

iTrader: (1)

Check your cat. Maybe is a small leak. Go to a muffler shop and ask to check for a leak. But the P0300 and P0305 sound more a ignition coil on spark 5. Also, maybe the spark plug # 5. How lond you not change that spark plugs wires or spark plugs?
Let me know.

clauddio09

thank you for the replies. Yes the plugs and wires are new. I read on another thread that sometimes the alternator causes issues so I pulled mine off and took it to get tested and to my surprise they told me it was bad ... I took it to another place and they also said it was bad. so I thought I had found the source of the misfires and purchased a new alternator but after test driving, the codes came right back. I also removed the cat converters to inspect them and was blown away when I found that they have been hollowed out, all 3 of them. I guess the guy that sold me the car got one of those illegal smog check certification....lesson learned for me. so now I know why I got cat codes but the misfires remain a mistery....any ideas would be greatly appreciated....

Mcon

iTrader: (1)

What code is it" P0300 or P0305, or both?

clauddio09

I'm getting codes 300, 306 and 305

Mcon

iTrader: (1)

Code P300 is multiple random missfire

Code P3005 Possible causes?

- Faulty spark plug 5
- Clogged or faulty fuel injector 5
- Faulty ignition coil 5
- Fuel injector 5 harness is open or shorted
- Fuel injector 5 circuit poor electrical connection
- Ignition coil 5 harness is open or shorted
- Ignition coil 5 circuit poor electrical connection
- Insufficient cylinder 5 compression
- Incorrect fuel pressure
- Intake air leak

Code P0306ossible causes

- Faulty spark plug 6
- Clogged or faulty fuel injector 6
- Faulty ignition coil 6
- Fuel injector 6 harness is open or shorted
- Fuel injector 6 circuit poor electrical connection
- Ignition coil 6 harness is open or shorted
- Ignition coil 6 circuit poor electrical connection
- Insufficient cylinder 6 compression
- Incorrect fuel pressure
- Intake air leak

For me is a wire problem on your ignition coil or your last ignition coil that is bad and make the problem with your code. Also, to install the spark plugs you need to take out the throttle body and in the throttle body and intake manifold is a gasket do you check that gasket when you take out the throttle body? I remember that now because in my car was bad, bad, bad.

Mcon

iTrader: (1)

So, please check the throttle body gasket as well.

Mcon

iTrader: (1)

I add pictures tomorrow. Is late here in Florida. LOL

Mcon

iTrader: (1)

The wet area was the leak on the intake manifold side.





My intake manifold leak and also you can see the cover valve with all the mark and the residue of the leak.





Left side, the old intake manifold gasket and the right one, the new one. Check your intake manifold gasket. That also make all the code that you maybe have. I recommend some patience. I took about eight months to find the leak and the air hose that was broken and you saw in the previous pictures.

clauddio09

Thank you for the reply. Yes I replaced that gasket with a new one when I changed the spark plugs and wires. I also replaced the other 3 gaskets from the intake. So far this is what has been replaced with new lexus parts:
spark plugs
wires
intake manifold gaskets
fuel pump
alternator
new battery
igniter
I did not replace the coil packs because I borrowed the ones from my buddy's car which is the same year and model lexus and a good running car and my car still misfired so I don't think it's the coils.
what I find so strange about this issue is the fact that the CEL starts to flash indicating a major misfire but the car shows no symptoms...no rough idle or noticeable loss of power.

Mcon

iTrader: (1)

Do you clean the code with the code machine after you do all that work on your car?

Another thing that you can do is, disconnect both battery cables, positive and negative at night and in the next morning re install the cables to see if you delete that coes that might be in memory of the computer.