Legacy B4 RSK uneven power delivery when cold

[Andy_Mac]

So from cold there seems to be some wierd stuff going on with my legacy. This happens in all gears i\'ve tried, up to 2000rpm it runs sweet but once it gets over 2000rpm the power is kind of jerky, as if i\'m pulsing the accelerator slightly which i know i\'m not. Once its warmed up there\'s no sign of it whatsoever. Could this be some kind of sensor messing with the air/fuel ratio when cold and that the ratio when warmed up is ok?

[Guest]

Both my subarus have done that from cold till they warm up a bit for say ~1.5min. V5 and P2 forester same afm/engine in both.

Few things thrown around but coolant temp sensor and afm are commonest I think.

[boon]

Could be a wee miss - when were your plugs last done?

[Andy_Mac]

I think plugs are ok. Checked the two on the passenger side when i first got the car and they were some pretty brand new looking iridium ones, i made the assumption they would have changed all 4 at the same time but maybe its worth checking the other 2

[Andy_Mac]

If it was missing would you not expect it to increase in frequency as revs go up? This keeps roughly the same frequency but is just a larger pulse at higher revs

[D-Style]

Check Temp Sensor.

[tebbyj]

Also when was the fuel filter last changed?

Car needs more fuel when cold if the filters a bit clogged can cause a slight surge when accelerating when cold.

Any codes? Probably not a big enough problem to throw them but worth a look.

[G-unit]

every subaru ive had had been like that when cold

[Andy_Mac]

Na no codes

Yea quite a few threads i\'ve looked into say its quite common but never seem to give a straight up answer on what causes it, suppose if its common then its not really something thats major. Could it have anything to do with the ecu being setup for 100 octane jap fuel rather than 98 in nz?

[tebbyj]

It could be fuel but it doesn\'t sound major, i wouldn\'t worry about it.

Most subys will do something of the like when cold. Mine definitely do.

If its really bothering you just try some basic stuff, Injector cleaner, Clean air filter, Subaru upper engine cleaner, even just an ECU reset might help (bad batch of fuel = ECU compensation ETC.)

If its the very beginning of a sensor fault it will most likely get worse and when it does the car will most likely tell you with a CEL