Hey all
I have a 2008 Lexus IS350 with 106k miles.
2 weeks ago, I noticed my car is having trouble starting and it would only start when I step on the gas while pressing the start button but its been starting a little better now. (I dont know if this relates to my problem right now)
About a week ago, I notcied that my car drops RPM when I set my foot off the gas. It just goes from 3-5k RPM all the way down to 1k or less. I also notcied that my MPG keeps on going down and sometimes resets back to 0 when I start the car then goes back up to normal then goes back down all the way to 4 MPG.
It might be my fuel pump since I havent changed it once but theres also like a waterfall sound coming from the engine bay when I turn on my AC and you could hear it from inside the car.
Idle is pretty normal 600-900 RPM and it doesnt jerk but it pops a lot more often on idle now.

I just changed my spark plugs and ignition coils recently so they should be good. I also brought it to toyota when I shorted out my ignition with my headlights.

 

I forgot to metion.
It doesnt give me any codes even after resetting my ECU.
AC works fine as well.

 

that right here is what I will question. what did Toyota find during this? they only replaced the ignition?
I suspect there may be residual issues with this "short".

what you describe is definitely not normal, and very odd to a point I cannot just pinpoint it to a fuel, spark, idle, etc problem.

 

They said they only replaced the ignition and disconnected the wiring from my headlights that caused the short. I have the VLAND headlights and you have to use a different connector for the LED strips and plug it directly on the fusebox. Well they removed that and changed my ignition and car worked good as new after. I even drove it from New Mexico to Florida the day after and came back with no problems until recently.

 

Vacuum leaks come to mind as do cleaning the MAF. If the maf is dirty the ECM doesn't know the actual air volume into the engine and the idle will be erratic.

Also, you might want to clarify what replaced the ignition means. Ignition coils are one thing. The wiring harness is something else. Please clarify.

 

When I asked Toyota they said they fixed the wiring stuff and replaced some fuses.
I might just bring my car down to Toyota again and have them check it.