My car 2001GS300 had misfired on #2 (code P0302, P0300) and I replaced all spark plugs and wires and the coil for cylinder 2. It fixed the problem. A month later, once a while a symptom of misfire happened again but no code yet and I replaced the remaining 2 coils. It ran well for about 6 months and the symptom of misfired happened again once a while and the symptom became bad and check engine light came on with code P0301. I swapped the coils between cylinder and it worked well for a few months and symptom happen again. I replaced the fuel filter but it did not fixed. Took to dealer for diagnosis and they told me cylinder 1 misfired. They swapped the coils like me and it fixed the problem. After about few months it happened again. Took to dealer again and they told me they need to changed the spark plugs and wires. I told them plus, wires and coils were changed few months ago. They told me then they need to tare down the engine to do the leak test and it cost at least $500. I refused the service since I don't think the engine has compression issue since the misfire did not occur consistently. I took the car out and on the way home, the misfire symptom suddenly disappeared. it's kike the problem is intermittent. it also looks like if the problem occurs, removing coil and put it back or removing the electrical wire connecting to coil and plug it back, it fixes the problem for few thousands miles.
Does anyone have similar problem. I am not sure if the cam sensor cause this kind of misfire.

 

Maybe theres a problem with the harness. Any signs of melting or pinched wires? Is the plug inside the harness nice and clean with no build up? Electronics can be quite picky sometimes. One of the pins inside could be damaged in a way that its not making good connection.. IDK, just a thought

 

Also, check your air hose in your intake manifold. Code P300 It is a generic code and can be a few thinks including a air leak on the exhaust manifold, ignition coils, spark plugs wires or a spark plug.

 

Very true, but the 300 is paired with a cylinder code also, so its centralized

 

I dont read all your thread and the first thing I did was answering thinking about what I said earlier. But what you have to do is see if the electrical plugs of the coils are in good condition and make good contact with the coils. These connectors broken very quickly due to the heat that builds up in that area. In the auto parts also they sell a silicon for that connector to make better contact. If these connectors are wet you know that water and electricity will not flow and seamlessly blend and what we believe is that there not goocontact between the plug and the base of the coils and create misfire. Is basically what says Mr. Jokster say. Again, sorry for jump so fast and no read the full thread. But I hope this help you and you no need to spend to much $$ to fix your car.

 

Have a similar problem with intermittent misfiring. The culprit turned out to be a ECT thermal sensor which is located on the bottom drivers' side of the radiator. Not finding this particular sensor at any parts stores or dealerships (all have to be ordered) I opted to order the part myself with the help of lexuspartsnow.com. They are helpful and prompt on returning your calls or emails. Anyway, the that sensor tells the computer what the temperature of the engine is, whether it is just starting up or driving. Mine was showing that the engine was always running rich. So, I had a lot of carbon build-up on my spark plugs and and the exhaust. Anytime you order from these guys, you should have your VIN so can get the exact part. Will replace plugs and wires when I get the part.

 

Thanks for your hints. May be my car also has bad ECT thermal sensor. How did you find out the sensor was the culprit. Did you have the part number of the part? I recently change the wires, spark plug, coils so I think they should have good connection. I need to open the spark plug to see if carbon is built up.

Thanks,
Robo

 

Thanks, Will check out the connection.

 

Hello Solo4ewa,
Did you remember if the part number is 89422-30030? I could not find diagram that show the sensor on radiator but generic diagram. The part number of of water temperature sensor is shown in 89422 of below diagram
http://www.lexussouthatlantaparts.co...ssembly=757619

Thanks,
Robo

 

You are looking for is the ECT (Engine Coolant Temperature) sensor and that sensor is located by the intake manifold. See diagram in post #3 for a better reference.

https://www.clublexus.com/forums/gs-...xus-gs300.html

The radiator should have a drain bolt but do not mistake that and order the wrong part.

 

Solo4ewa mentioned he changed the sensor at the bottom of the radiator on driver side and I saw one on my car. Hopefully this will fix the problem. I opened the spark plugs and there was carbon built up. Changed a new one and drive for few days and carbon was built up again. I also change the coil connector housing so I have no idea what to change except the sensor at bottom of radiator.

 

I'm dealing with the same symptoms on my GS300. If I hear another pop, I'm getting this sensor since I've pretty much replaced everything.

 

I went to oreilly and purchased a ECT sensor that is replacement for part number 89422-30030 and the connector was not fit the one at the radiator. I realized that when the cable disconnected from the sensor/switch at the radiator, the fan running at maximum speed for just turn on the key without stating the engine.
I used touch scan software to scan to diagnose the car and the engine coolant temperature was around 185F even with the cables disconnected from the sensor/switch at the radiator. The temp gauge on dash board also worked correctly with cables disconnected. I ran the car several mile but there was no code. It look like the sensor/switch is not the ECT that sends temperature info to ECU.

 

Yes there is a sensor thats connected to your radiator..... sorry to burst your bubble.

 

Part no.: 84422-30030 is the sensor just under your intake manifold. It is the first sensor that is in the head not the block. Difficult to reach. Had to move a lot of peripheral stuff out of the way just reach it. I believe it was a 19mm socket with a lot of room for the plastic connector. The other part on the radiator Part no.: 89428. I found that these sensors are vehicle specific. Might look like others but have variations. ALWAYS use your VIN when ordering. These two sensors are inter-related to tell the ECM what temperature the engine is running at.