Turning on AC at idle causes RPMs to jump around eventually stalling the car
 

As stated in title the car will start up and drive fine but if the AC is turned on when idling the engine seems unable to handle the extra load and RPMs become very erratic. After a few seconds or if AC is turned off the car stalls. The navigation screen displays the message "check air conditioner" but no dash lights are on.

I have cleaned the throttle body out as much as I could with the drive by wire system limiting valve movement and no change. Not sure now if the whole throttle body needs replacing or if the problem could be with the compressor or elsewhere. It is a 2007 IS 250.

Any help in diagnosing the issue is greatly appreciated.

your IAC (Idle Air Control) has a problem or your alternator is weakening, but 1st try the eazy step

1, use a jump battery pack connect to your battery and start the car turn on AC if the car runs fine then it's your battery or alternator.
2, Have you tune up your car recently ? that IAC uses some of engine Horsepower to pump the AC it puts ton of load on engine and that may causes the idle drops and stall the car, the Reason why you don't buy i4 Cylinders car and turn on AC in the hot summer. ya i know our lexus is V6 but 2.5 is too little.
3, Clean Throttle body and correct the IAC, i don't know how do i clean throttle body for Lexus IS250 honestly i never did before. only Toyota.

Don't forget to clean MAP sensor as well

Thanks for the replies.

I don't have a jump starter to test the AC so I guess I'll try and do a more thorough cleaning of the intake systems.

The throttle is drive by wire so there isn't an IAC valve correct? Second, if I disconnect and pull the throttle body out can I push on the butterfly valve to manually open it so I can get a good clean around the plate? I'm worried about messing up the sensor or harming the stepper motor.

I'll clean the MAP sensor as well, do you know if there is a MAF sensor as well or just the one?

Thanks again.

You can pull DTC's for the HVAC system through your nav screen on these models. I don't remember the exact procedure because it has been a while since i've actually done it.
Try this:
- With the car off press and hold the "auto" and "recirc/fresh" buttons
- while holding them, turn the ignintion to ON
- let go of the buttons and the panel lights will flash and such during the indicator check. It should pop up DTC's for the HVAC system.

I think if you push the recirc button again it will do an actuator check as well.

Thanks, I didn't know that. I'll give that a shot when I get home.

I also noticed after turning on the AC while driving that it only blows out warm air now and the compressor clutch isn't engaging at all from what I can see. Seems like it might be more of an issue with the compressor system rather than an idle problem as I'd originally thought.

Yep good thought, check that too while you there :cool:

So I'm going to try replacing the compressor. You can get a kit online with new compressor, o-rings, drier, expansion valves, and some refrigerant oil. I'm going to get the refrigerant reclaimed legally by someone and then try and flush/replace the new components at home before bringing it back to be evacuated and recharged at a shop.

One question is does anyone know where the expansion valves are on this model? (2007 is 250). Will I have to take apart the dash to get to the evaporator and replace them?

And has anyone tried flushing their AC system before with good results?

Thanks.

Take a look at this diagram, #12 is the expansion valve, looks like it might be tucked inside the dash panel.


http://www.mylparts.com/parts/2007/L...iagram=8916080

The IS does not have an IAC valve. The ECU controls idle using the throttle body and ETCS-i.

Jeff

Update: I ended up having the compressor/clutch assembly replaced by the local shop because I didn't want to deal with proper removal of the refrigerant in the system. The compressor was completely seized up and after replacing this component the AC is running perfectly cold again with no problems at idle startup. Fairly pricy repair but worth it to get AC back on for the rest of the summer.