Hesitant until warm and hard to start when warm.
 

My iMpreza classic hesitates when cold until it comes on boost

Also when warm sometimes turns over a few times before it will start. But always starts first time when cold

Any ideas :(

could be the water temperature sender for the ecu.

Would there be any other symptoms? I thought it was maff related at first. From cold it would not idle well until warm. Replaced that and it sorted that out. With the temp sender could it bring up a fault code in some circumstances?

Sorry to jump on but my farther in law has a bug and his starts fine cold but won't when hot and when it does after a fair few attempts chucks out a bit of smoke? Would this also relate to the water temp sender? :)

also i have read somewhere if its the temp sensor the fans will come on straight away as it believes its hot??

thanks

i had a simular issue on my my96 turbo wagon turned out to be front o2 sensor causing the MAF to over compinsate. didn't throw up a CEL cos is was kinda working just being lazy. i spent alot time chasing a hesitation issue and it seems there could be alot of causes, in the end i took it to a specialist and got it on a rolling road they sorted it within a hour.

I would alos suggest checking the water levels i have the starting issue you described it's happens when i'm low on water and at the moment thats quite often because i'm using about 2 liters of water evey 100 miles. lol

It chucked up a code in the end as was knock sensor so replaced it seems ok now although it took a while for idle to establish itself after ecu reset.