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Okay where to begin, I have a 2007 IS350 with almost 97k miles on it, and the last few weeks I have run into nothing but problems. First symptons the car was running like garbage it was stubbling and bogging at idle and would start shaking really bad once I got about 40mph. Then it started over heating, I thought it was a bad coolant temp sensor cause my gauge had been going all crazy, it goes all the way hot then drops dramatically to cold then middle then back up, back down just all the time. I couldnt figure it out so I took it to the mechanic shop and they did some diagnostics and found the the radiator cap was missing the pressure pin on the inside, replaced it and it was running fine. Then the car was doing the same thing, expect it felt alot worse there was no power and it was still stubbling really bad at idle. I went to autozone and got the codes pulled and they were
P0302
P0304
P0300
and
P0117
So misfires and then engine coolant circuit low input
I changed out the spark plugs a few days ago (much needed) and its seemed to have fix my idle and loss of power problem. I reset the ECU and then check engine light came back, this time its just throwing P0117 and P0420, I figured my sensor was bad and got a new sensor. Only problem is I have no clue where the sensor is on this car. I have tried searching and looking and I cant find it anywhere. I tried calling lexus and the guy in the service dep. told me that this car doesnt have an "engine coolant temp sensor" so he has no idea what part I bought. Now I am just at a loss I dont know where to go from here. So far I have changed the waterpump (a few months ago), thermostat, and spark plugs. My symptoms still are sometimes the car runs great and doesnt seem like its missing or having stubbling problems and other times I start it and it does. I will just be rolling forward in drive no gas and it kind of jerks back and forth. My engine temp gauge still flutuates up and down up and down but the car doesnt overheat or get hot. As for the cat code I havent a clue besides maybe the cat going bad or o2 sensors. Also my heater will work somedays and other days the heater doesnt work. I cant figure anything out and usually I am pretty mechanically inclined I can do most work on my own. If anyone has any ideas or any help please please let me know!
Thanks
Also I dont know if it would really effect anything but when the car overheated I had to get more coolant for it and all the autoparts stores dont carry the toyota red coolant, it has to be ordered and unfortunately I needed my car for work. So I had to buy just the mix with any color coolant. It didnt mix with any of the old stuff it was completely flushed and I figured it was okay for the time being, its only been in a week or so I can do a coolant flush and put in the correct kind. If you have ANY help at all or need to know anything else just let me know!
 

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Anytime a car overheats and gets into the the readline, there is always a possibility of damage to the block or headgasket. I would think the P0420 code is not related to the coolant temperature issue, however, if your engine headgasket/internal has suffered some damage, the downstream O2 would pick up on that and/or can be damaged. Bank 1 sensor 2 is on the passenger side after the Cat. From what i can tell, there is a coolant temperature sensor on the ISX50 cars because I am able to find it as a replacement part. Is it like in the image below? P0117 means Engine Coolant Temperature Circuit Low Input, so i would think that the sensor is bad. If it keeping the radiator fans on all the time? Obviously, your coolant temperature should never fluctuate much from operating temp, once it warms up. Whenever your car overheated, you expelled a decent amount of fluid out of the reservoir. so for that, i would just top off and keep an eye on it's level. I would definitely consider a flush as you should not mix toyota red long life fluid with any other type because it can create a jelling effect. Unfortunatly, through an extensive search, i cannot find the location of the sensor. It has to be located on the radiator or in it's vicinity. Let me look into this further...

http://www.car-stuff.com/includes/secure/popup.php?type=more&image=aHR0cDovL3d3dy5jYXItc3R1ZmYuY29tL3N0b3JlL2ltYWdlcy9wcm9kaW1hZ2UvaW1hZ2VzL3JlcGxhY2VtZW50L3JlcHQzMTgzMDEuanBn&title=UmVwbGFjZW1lbnQgQ29vbGFudCBUZW1wZXJhdHVyZSBTZW5zb3I=&text=Q09PTEFOVCBURU1QRVJBVFVSRSBTRU5TT1IgLS0gUG9zdCB0eXBlOyAyLXByb25nIG1hbGUgdGVybWluYWw7IEEgaGlnaCBxdWFsaXR5LCBPRSByZXBsYWNlbWVudCBjb29sYW50IHRlbXBlcmF0dXJlIHNlbnNvcjsgQmFja2VkIGJ5IDEteWVhciwgdW5saW1pdGVkLW1pbGVhZ2Ugd2FycmFudHku
 

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Okay, I talked with my freind who works at Lexus and asked him about the location of this sensor. He told me it's listed as a water temperature sensor and your right, there is no coolant sensor actually labeled coolant in their parts index, so I guess they don't label it as "coolant". This sensor is located on passengerside of the engine block and towards the rear of the motor. This is the best info I can get ya for this location.


The first generations coolant sensor is located on the radiator, as with GM cars, so I'm supprised it's not located there as well.
 
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