2003 NA Forester runs better when cold

[dylanpenhale]

My 2003 NA Forester runs really well when it's just started but seems
to have less power when warm and on hot days. I realise that the auto
choke is richining up the mix which may mean that the usual mix is to
lean and also that there is a temp sensor in the airbox that may be
having an effect. It's been checked twice at service time and it's
always been OK'ed by the service people.

Can anyone tell me what it might be. I have heard you can add a
resister or something to the temp sensor but this may well be a gimic.
Any ideas?

 

[Mike]

Cold air is denser,...that means more power. The car will run a bit stronger
when cold because of a cooler intake charge before the parts under the hood
get heat soaked. And since the car takes the air in from outside the engine
bay, when its cold outside you are geting a cooler intake charge .