strange idle!

[m03nn400]

when my 172's idling after warming up if i put the heater speed down to 2 bars the car idles at 1000rpm, if i put the heater up to full it idles at 750rpm. Anyone know why?!? please help as its doing my head in

 

[mike]

Is this witht he air con on?? It's due to more power being needed to run the air con I think? Mine does it too, even worse if you bung the heated rear screen on too!!

 

[m03nn400]

no the air con isn't on, when i put the air con on it goes even lower, to 500rpm

 

[Jacoob1976]

when my 172's idling after warming up if i put the heater speed down to 2 bars the car idles at 1000rpm, if i put the heater up to full it idles at 750rpm. Anyone know why?!? please help as its doing my head in

It would do, as the heater/air con draws the power from the engine, or maybe i'm wrong but i noticed things like that my self with my golf

 

[m03nn400]

i've just never noticed it before until i took the throttle off and cleaned it up, but i've taken it off before to take the plenum chamber off and didn't have any problems so dunno?!?