Hello everyone, i have a 2002 lexus es300 with about 240k miles on it, about 5 weeks ago i had a misfire, a friend and I replaced spark plugs of cylinders 2,4,5,6 (1 and 3 are very hard to get to) and changed coil pack of cylinder 6 a lil later as it misfired again. anyways about a week later i started my car to go to work and very obviously felt a misfire and saw the rpm’s jumping around between 400-1600 when the car always idles about 800-900, i quickly turned the car off and asked my step dad to come see, i started it again and it ran fine, later that night after work it did the same thing and i ran codes and got a cylinder 1,3,5 misfire codes but after about 30 seconds car was fine and no more codes, at first i thought maybe it only did it when the car was super cold (but never done this any other winter) and i live in colorado where the weather has been cold recently. but after about a week the car started and fine as it did before, there was a hole in my intake tubing pass the sensor and my friend assumed it’s just running rough because of that (and my header was red hot, so we knew it was running rich), well i replaced that anyways and it has been fine, but today (15 degrees and snow) when i started my car it did the super rough idle and mis firing and rpm’s being weird thing again, any one know why? any one know what i can do? what i can replace? i’m not the most knowledgeable with cars, but please ask questions and i’ll give my best answer.

 

Hello,

What parts did you use for the repairs?

Spark plugs should always be replaced at once, that alone can be a reason for a very bad idle, basically 1/3 of your engine may be misfiring. Bad spark plugs are one of the most common reasons for fried coils, as the plugs ages and gets gunked up, it is getting increasingly hard for the coil to strike through said spark plug, greatly increasing strain on the coil. To fix an issue, you need to start with known problems, even if they are not the culprit at the moment, it doesn't mean that they won't come haunting you later.

Check Engine Live Data as well, look for Misfire Count for each cylinder and Fuel Trims, as well as MAF and Temperature sensor readouts, post them here. In short, Misfire count will tell if there is a misfire, Fuel Trims specify how rich or lean the engine runs, MAF sensor is how much air the engine consumes, and Temperature sensor is responsible for Warm-Up modes, if the car thinks that the engine is always cold even though it is at operating temperature, the mixture will be richer than normal accordingly.

Hope this helps and best of luck!

 

Valve seals.

If your intake valve seals are starting to fail (and why shouldn't they be? Your car is 240,000 miles old after all) well, it doesn't matter how many new parts you throw at this problem, the problem isn't going to go away.

The good news is there are some pretty good re-sealing products on the market which will often rescue valve seals (if they're still saveable). You add the product to your engine oil.

Also, there are some well known tests you can perform to ascertain if your valve seals are failing. Time to start reading.