Idle rise and shudder turning AC on

[Worzella]

I know that when you turn on your air con in your car, the ECU raises the idle a bit to compensate for the compressor load on the motor.


My LR4 idles at a nice 600 RPM without AC on, but lately, when I turn it on it raises RPM to 1200 and there is a noticable shudder in the engine that can be felt and heard in the interior. Turn AC off and lowers to smooth 600 again.


No codes but any ideas? I have not replaced the MAP sensor yet, but I am wondering if doing that and cleaning (maybe replacing?) two MAF sensors would help along with a good intake throttle body cleaning.


Car has 147000 miles and no record of these sensors being replaced

 

[Rover Range]

Try disconnecting the battery for 15 minutes.
That resets the PCM.

 

[Worzella]

Thanks but then the system might just relearn incorrect data/behavior. I guess I will discon battery when I do the cleaning work and MAP replacement. Let it relearn with better info I hope

 

[Rover Range]

Thanks but then the system might just relearn incorrect data/behavior.

In that case. The PCM adaptions will have to be reset with a scan tool.
I would clean the throttle body too.

 

[Worzella]

Interesting twist.. started car a few days later (my girlfriend drives it most days) and idle sat solid about 6-700 whether AC was on or not and no shudder. So whatever was going on was intermittent. I will let sleeping dogs lie until it happens again I guess.