i have a problem with engine rev's hi on cold start. It's 99wrx and has autronics smc plug and play ecu.
I've just got back from work and it's first time this has happen, rev's at 2000rpm for very short time then sits on 4200rpm.

help please.

Thermostat

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06 sti

problem fixed. The idle air control valve was suck or not working. used a cleaner and problem solved.
ill be replacing iacv

mine used to do the same with autronics, i just thought it was normal?