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Discussion Starter · #1 · (Edited)
Hey guys, thanks for having me.

I've got a pretty annoying problem with my 2006 IS250 with 190k on the clock.

I changed the spark plugs on them with denso iridium TT, applied anti-seize and torqued them to under spec. Applied dielectric grease on the porcelain and under the boot with a que tip.
While I was there I made sure to clean the throttle body that was a little dirty. I moved the actuator by hand slowly and thoughtfully and used degreaser (I had no TB/carby cleaner) and made sure it was spotless. I also cleaned the tops of the intake valves and plates and saw there was carbon build-up in the cylinder. Normal right. I replaced the intake gaskets but not the TB gasket as it looked fine and didn't come with my pack. I had the battery disconnected this whole time.

I finished up everything and put the intake back on as required and started the car. After a few tries (wd40 got into the engine from soaking the spark plugs) the car turned on and I warmed it up to operating temperature. Once at that point and the idle settled to around 900 in park it threw a p0505 code that was pending. A few more startups and the same thing, only confirmed. The car idle wasn't particularly erratic, but you could certainly hear and feel it being a little off. I cleared the code but they remained. It will also sometimes trigger the engine light and a vsc error with traction control but that doesn't always happen.
The code will only throw once the car has reached operating temperature.
I have done an oil change, filter change a week or two before that - running fine.
I know the code relates to the idle speed control system malfunction but this could point to many things. Vacuum leak, ISC failure, apparently PCV piping, TB, Maf?

I've done a lot of troubleshooting on this with the help of a facebook post and another lexus forum.
I've also done extensive google searching, searching through this forum and others for keywords on the issue. Nothing has since solved it.

What I've done so far:
Been over every connector/sensor/harness to see any possible error - nothing
Re-cleaned the throttle body AGAIN (cleaned a single spec off of it the second time its that clean) - used TB cleaner this time
Re seated the entire intake again and made sure each gasket was sitting properly.
Re seated the TB and made sure it was seated properly
Sprayed the intake and TB with TB cleaner to see if I could find vacuum leaks - nothing
Re-set the ECU/ECM so many times with battery + fuse reset
Tested to see if the alternator was faulty - its fine

I've now ordered another used TB from ebay for cheap but I genuinely am running out of ideas.
I just drove the car 700ks for a trip and it didn't miss a beat doing mostly 80-110km/hr along the way. The car is getting insanley good mileage now (33mpg or 7.1L/100km - although they're highway numbers) The only problem is the code and weird idle.
I've used the 'car scanner' with a bluetooth dongle and backed up the code with a more expensive handheld code reader.
I have a freeze frame of the engine sensors when the code gets thrown for those wondering which I will include.
I'm willing to try anything and I'm desperate for help.

The other forum mentioned how my airflow at idle was high at 3.42g/sec and never being under 3g/sec the entire time. Possible TB being open too much to have the car hit idle specs? I duno, I'm only speculating.

Thank you for reading and I will promptly reply to all fast. Any help is greatly appreciated.


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