My vehicle seems to have lost half it's performance and after spending the last week "lurking" on the forum and trying to figure it out myself I have decided to see if anybody can make sense of what I have learned. My vehicle is completely stock

How it started
- My vehicle went for a service maybe 2 weeks ago, got it back, no issues
- About a week ago I was driving home and as I was overtaking, the extra power that normally kicks in at about ~4 000 rpm seemed to kick in for a second and then all of a sudden it dissappeared (motor still pulling but not like it usually does). I was close to home and there were no engine lights so I put it down to paranoia and parked off for the night.
- The next morning, I took a car for a drive and the power boost at 4 000 rpm was completely gone. Having lived with the issue for a week it seems that the higher the revs, the more power seems to be missing (the revs climb incredibly slowly after ~5 500 rpm and the speed climbs very slowly)
- This morning, I used CarScanner to measure my 0 - 100km/h to make sure I wasn't just going crazy. 12 seconds on Sport S+. By my own, very scientific measurement, that means I have lost a lot of power.

What I have done
- Cleaned the MAF (about a week ago and travelled maybe 100km since then
- Got myself an ELM327 and the CarScanner app. Also collected 2 trips of data but I think I need the pro version to record all metrics

ECU data that I have noted while troubleshooting
- Throttle position sensor opens to 80% when I put my foot down. Not sure if this is normal? I figured this metric might help to identify whether this is a throttle body issue but doesn't seem like it
- MAF airflow at idle is about 4g/sec. On a trip in traffic it went up to a max of about 120g/sec. Tomorrow I will log it on car scanner to see what it peaks at when I try push the car
- Air intake temperature was showing way above the outside temperature on the first trip I recorded (20 degrees celcius difference). On the second trip I recorded it was much closer (4 degrees celcius difference)
- There is a metric "ambient air temperature" but it seems completely out of whack. Recording a starting temperature of 50 degrees celcius when it is 8 degrees outside. Weird thing is that the dash is showing the right temperature so I think I just don't understand this metric

I am thinking of cleaning the throttle body anyway this weekend just because I don't think it can do any harm but I am getting worried that this is an issue with the VVT-i system.

Is there any other data that I should be looking at to try figure this issue out? Any other "easy" fixes I can attempt before taking it to the dealership?

 

With the key on engine off, shouldnt your TPS go to 100% with the pedal to the floor?

 

I'll chime in with some data from my 2015 IS350:

• Mass Air Flow
  • Idle (~650 rpm): 2.8-3.2 g/s
  • Wide Open Throttle: ~180 g/s
• Absolute Throttle Position
  • Idle: 15%
  • Wide Open Throttle: 80%
• Intake Air Temperature
  • Vehicle moving: typically reads around 5 C above ambient air temperature
  • Vehicle stationery: typically reads >5 C higher than ambient air temperature

I am no mechanic but I'd check fuel trims, they should be around 0% or very close to it. Have you checked if your air filter is clogged?

 

Based on what I had read online, not necessarily. Matroushi's data below seems to confirm that

Thanks for this data, very helpful to have a benchmark. My MAF and throttle values match with yours. I will need to log my air intake temps in my next few trips.

I did end up swapping out my air filter because I noted it was dirty and this does seem to have slightly improved things. Very weird that Lexus has not changed my air filter two 15 000km services, is that normal? Unfortunately, I do not have the F-Sport intake with re-usable filter - still deciding whether it is worthwhile.

The VVT kick is back but not consistent at all (in terms of both the RPM at which it kicks in and if it even does). In the last few days I have begun to notice that the colder the car is, the more likely the VVT kick is to behave normally. If I stop at the shops on the way home from work and have a warm start, the VVT kick is more inconsistent.

My fuel trims were nowhere close to zero, and looking at some of my data from when the issue first arose:

• Long term fuel trim
  • Bank 1 : -4% to -6%
  • Bank 2 : -5% to -10%
• Short term fuel trim
  • Bank 1 : -1% to -2%
  • Bank 2 : 0% to -3%

Data above is the movements in the course of one trip, not sure if it is normal for long term trims to swing that much on a single trip? On another trip I had short term fuel trims of 4%. I am going to upgrade to the pro version of CarScanner to get more data because for some reason it only captures data if I am looking at it.

Another anomaly I forgot to mention in my initial post was that my fuel consumption was creeping higher and higher each day. I was on 11.9lt/100km and am now on 13.5lt/100km. I also noted that the exhaust fumes were cloudier than usual and more noxious. The air filter has improved this quiet allot but I believe this also indicates inefficient combustion. Maybe the car is just taking very long to "re-learn" in terms of the long term fuel trim?

Catalytic convertors is also on my radar given the issues when warm but my MAF rate seems normal so I doubt these are the issue.