Issues with Lexus ES 300 possibly transmission, I think not

I’ve had many issues with the a 1999 Lexus ES 300 recently.  It all started when the car started to drive funny; when at a constant 60 MPH, the car’s RPMs would be higher than normal, at about 4000 RPM instead of being around 2500 RPM.  This occurred at any speed, even at 30 MPH, the car’s engine felt and sounded like it was doing too much work.  To top things off,  the check engine sign and traction sign have been light on for an even longer time.

When attaching the scanner to the car, the codes that were FIRST appearing was for misfiring (this is what my mechanic told me).  I had to change 3 coils (located above the spark plugs I believe); and I went ahead and got those replaced.  A few weeks later, another coil had to be replaced – I went ahead and got this changed as well.  This car has 6 in total, so I ended up changing 4 out of the 6 coils.

Even after those repairs,  the car still seemed to be riding the same – at times, after accelerating from a traffic light, the car would ‘slip’ and wouldn’t speed up until I quickly shift from neutral then back to drive.  This seemed like a transmission issue (according to my mechanic after explaining to him what had happened).  After doing research online, I found that this didn’t seem to be a transmission problem but a knock sensor problem.  I had the mechanic scan the car again, and found the codes P0171 and P0330 appear.

After reading various articles online, I found that P0330 = knock sensor and fixing this would fix the ‘slipping’ issue.  After replacing one of the knock sensors (this car has two of them I believe), the ‘slipping’ went away and the gas mileage was much better as well.  Thank you, it’s a great feeling not having to change the transmission and spending around $2000 more for nothing.  Along with this knock sensor replacement though, there were a few other requirements: changed 2 intake mainfold gaskets, 1 pyaman gasket, and 1 mass inflow sensor.

Even though the car runs great now, the lights for check engine and traction sign are still on.  Running the car through the scanner again, I see a P0446 code which seems like something to do with an Evaporative Emmission Control System Vent Control Circuit or EVAP.  Hopefully this will be a quick fix such as changing the gas cap but if not, my mechanic will let me know what to change/replace.





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