paradox

Hi Everyone: I just purchased a 2000 GS400 to replace a 95LS that someone rear ended and was totalled by the insurance company. This morning, while I was at a stoplight, the tach jumped up from about 750 or so to about 1200 RPMs. I let the car move forward a bit, then hit the brake again, at which point the idle returned to normal. About 5 mins later, it happened once more at another red light. I repeated the same process and the idle speed again dropped down to normal..... Situation did not recur after that. The car was fully warmed up (driven @ 45 MPH for about 20 mins or so) before the first instance of this occurred. I did a search for "high idle" etc before posting, but didn't encounter anything that reflected my particular scenario.....
Has anyone here ever experienced this problem, and how was it resolved? Any ideas or thoughts would be very much appreciated!

TruPlaya26

iTrader: (4)

Did you have the A/C on? maybe it jumped a little bit since the A/C turned on

paradox

^ Nope, no A/C, was pretty cold this AM, even in GA ..... Also, no CEL.... Good thought though!

Chris2

iTrader: (2)

Did you left the car wam up or just jumped in and drove off? Mine was doing the same thing when I first got it. Had to learn to warm it up but did not cause too much of a problem.

paradox

Yeah I usually let the car run a few mins before driving it.... I took it in to have a technician try to recreate this and he was unable to. Said it looked normal to him.... I will need to follow up with this though. Problem as it see it is this.... you get to a stop light, depress the brake with just the requisite amount of force needed, then the idle suddenly jumps up, the car jerks forward and you hit the car in front of you....
I was thinking maybe the TPS, but wouldn't that trigger the CEL?

Kaluna

Sounds like an IAC valve starting to go bad. The IAC is going to compensate for any load thats put on the engine. It should keep the idle constant. If your mechanic has a Solus or Modus reader or equiv. have him adjust the IAC trim & see if its responding when you hit the brake. If the reading spikes its most likely the IAC going bad. I had this happen on my 5VZ in my Tacoma with the same symptoms. My IAC wouldnt even respond to the diagnostic imputs. Its worth a try before going deeper. Like you said a TPS could also be a culprit just because of the high jump in RPM. Hard to tell without it acting up & logging it.

diamondmit

...on "Auto" setting, it may intermittently select AC, even if the outside temperature is quite cold. I don't think this is very likely to be honest, because the tech that checked your car out certainly would have looked into this, but stranger things have happened.

Let us know what you find.

regards
dd

paradox

Thanks to everyone who responded to this thread. I just brought home the car from the Lexus dealership. The tech kept it overnight and tested again this morning, and was unable to recreate the condition.... Also said there were no codes. I did mention what Kaluna suggested (excellent suggestion BTW), and will take it back next week for further troubleshooting. Meanwhile, I'll monitor and try to get this to occur again, and try to pinpoint what conditions might trigger it. I'll post updates.....

Kaluna

Good luck with finding it. My Tacoma's problem although intermitent was a little more persistant in rearing its ugly head. Just keep at it, these things can be irritating to find especially since YOU know it happened. Keep us posted on what they find.