Noticed this today while coming home sitting at a few traffic lights...the RPMs would get pretty low (300-400) and the car would rev itself back up to 800-900 to keep it from stalling. I couldn't replicate it in my garage sitting there for about 5 minutes. This happened while in manual+sport. Anybody have any idea what it is that may have caused that?

 

Just a guess, maybe a dirty fuel filter?

 

battery??????

 

Doubt if it is the battery since the alternator should supply enough power at idle.

Could be fuel, but it is more likely that an Idle Air Control is not working properly and that should set a code since it is part of the emissions system. If it does it again see the dealer or get a code reader.

 

Ya I wouldn't think it would be the battery either. I'll keep an eye on it and if it does it again will make a trip up to Lexus, still have 3 more years of my extended warranty maybe I can get something out of it haha

 

maf sensor is dirty or dirty throttle body

 

i don't know what's causing it, but mine did that once. my last GS350 did that serveral times during 4 yrs of ownership, but didn't stall..

 

Mine does this once in a while as well. Most of the time its after blasting down one of my favourite roads that ends in a long light. Its like the fuel trims change just enough during WOT that idle is impacted.

No CEL for me. I usually just make sure the DRLs and AC are one which puts enough load on the engine to force a more stable idle.

 

The ECM ignores ST fuel trim at anything over 74% throttle (pure open loop with LT fuel trim arbitrarily applied to the maps), so the ECM isn't learning anything about trim at WOT according to Toyota's documentation starting with TCCS way back in the 80s.

There is a whole lot of interdependent checking the ECM does to validate the various sensors are all working correctly, and there are some short test patterns it runs intermittently to validate the sensors are responding within predefined parameters. If a sensor does not respond to this test with the anticipated value, the ECM will normally set a DTC or DTC pending if it only happened once or twice.

It's possible you just happened to find a moment when the ECM was mucking with things and you caught it in a test mode when it should not have been. I'd still have the DTCs checked and especially any pending codes.

I see your secondary cats are removed. Were the secondary O2 sensors possibly damaged when you did this?

 

your wealth of knowledge never ceases to amaze me lol. It hasn't done anything since and I've been driving it everyday so I think perhaps you are right re test mode. I don't think anything was damaged with the cat delete, the guy that did it said the sensors came off and went back in nice and easy.

 

MAF sensor or more likely throttle bodies need cleaning.

 

The same this happened to me two weekends ago. I had just started the car and the car seemed as though it had difficulties staying on, dropping in RPM almost stalling. The issue lasted about 1.5 min and then the car went back to normal. No CEL. I haven't thought much of it since then.