Engine Rev Fluctuating With Aircon On

[SauRoNZA]

Mine does it on my Hyundai Accent 1.6 2006 model for a little bit when the aircon kicks in. But car adjust accordingly. It's not that bad though and revs don't dip that low.

Good chance the rev counter just isn’t very accurate so low down.

As long as it’s not stuttering it’s just fine.

 

[HAL 9000]

Here's what Google AI has to say:

AI Overview


The "idle speed compensator" on a Hyundai Atos is actually the Idle Air Control Valve (IACV) or Idle Air Control Actuator, an electronic component that regulates the amount of air entering the engine to maintain a stable idle speed, preventing the engine from stalling when the vehicle is stopped. Its OEM part number is often 35150-02600 for Atos models, though it's essential to verify the exact number for your specific vehicle.

What the IACV does:

• Controls engine RPM:
  When your car is idling, the IACV allows a small, controlled amount of air to bypass the closed throttle, maintaining a consistent engine speed.
  
  
• Adjusts for conditions:
  The vehicle's computer (ECU) monitors engine load and temperature, signaling the IACV to adjust the airflow to keep the engine running smoothly.
  
  
• Improves performance:
  A properly functioning IACV contributes to improved fuel efficiency and smooth cold starts.
  
  Common Problems and Solutions:

• Symptoms of a faulty IACV:
  A malfunctioning IACV can lead to unstable or high RPMs at idle, or even engine stalling.
• Troubleshooting:
  • Clean the IACV: Carbon buildup can restrict airflow, so cleaning the valve and the throttle body may resolve the issue.
  • Check for vacuum leaks: Unstable idle can also be caused by vacuum leaks around the intake manifold and other hoses.
  • Test electrical connections: Ensure the electrical connections to the IACV are secure and free from corrosion.
  • Replace the IACV: If cleaning and checking for leaks doesn't help, the IACV may need to be replaced.

 

[W@P]

It's the turbo button. When you want to overtake or dice, you press it so it's off.
Switch it on and floor the kak out of the car in 1st/2nd gear while still pulling, switch it off, and feel the boost you get.

PS, nothing revs like a rental.

 

[Mariner]

On a big diesel, the effects of the air conditioning cycling can be heard when idling. The diesel clatter gets markedly louder when it cycles on. Diesels will adjust their fuel rack to compensate for load and maintain the same revs, resulting in more noise for the same revs. So, on a small petrol engine, losing revs shouldn't be a concern.

 

[airborne]

Yes, but traditionally all aircon compressor pumps are mechanically driven, not electrically so it being on shouldn't have any affect on the alternator. This obviously isn't true if the aircon compressor pump is electrically driven but I don't know how many modern cars use electrically driven aircon compressor pumps, I have only seen retro fit kits like VWSA did for some CitiGolf's. I don't recall @Ockie saying that his car's rpm dips all the time, only when the aircon was on...

I didn't say that the aircon pump was electrical just that if the battery was faulty and the alternator was having to charge the battery and power the whole car it coudl potentially be putting an unusual load on the engine at idle in combination with the aircon being on at the same time. But in any case the chance is slim that that is the issue, it's probably more a throttle body/sensor/ecu issue.

On a big diesel, the effects of the air conditioning cycling can be heard when idling. The diesel clatter gets markedly louder when it cycles on. Diesels will adjust their fuel rack to compensate for load and maintain the same revs, resulting in more noise for the same revs. So, on a small petrol engine, losing revs shouldn't be a concern.

The issue is not the revs dropping with the aircon coming on but rather it dropping so much, all the way to 500rpm from 1000rpm.