Weird Idle with AC on/off (1 Viewer)

[at1992]

Hi,

I have a 1997, Lexus LX450.
1FZ-FE. Stock.

You guys know when the AC is one the compressor AC clutch will not engage all the time right. Its engaging and turn off itself.

So when the I have the AC on but compressor clutch is not engage its idle low and a bit tiny rough (600rpm) and like 1 minute later when the AC clutch is engage again the RPM goes up to 1.2K RPM and no more rough idle.

The engine is for sure louder with that high RPM.

What can be the cause of the drop and increase of the RPM?

 

[jvazquez53]

If you find the answer let me know, I asked this months ago and no good answers...

 

[Formulaonehd]

I think you will find the 1FZFE is notorious for this symptom. I know mine does. These aircons suck a lot of life out of the engine so the RPM will jump a fair bit and make a bit of noise with the compressor and clutch engaging and disengaging. If you live in a hot climate your temp guage will shoot up if the system is not set to 'recycle air' and just drawing from the exterior vents (be mindful of this as well)

The drop in the RPM is normal for these cars in my opinion. You can overcome this by adjusting your throttle cable to increase the revs at idle but the engine will be slightly louder at 'aircon off 'idle

 

[ppc]

The ECM controls idle, there is no "idle adjustment". The increase in RPM the OP described is perfectly normal. When the AC compressor is engaged the ECM increases the idle RPM to account for the additional load on the engine. When the transmission is not in gear then 1200 RPM seems normal. When in gear with the brake applied the RPM will be significantly less. At normal operating temp the idle should be 650 RPM when the AC is turned off or the compressor is not engaged. If it running rough then there are other causes such as a vacuum leak, fouled spark plugs, dirty throttle body, IAC passages etc. When was the last time any maintenance has been performed? Distributor cap, rotor, wires and spark plugs are items that need replacement periodically.