I just recently(3 days ago) got my 2006 STi and noticed that after the engine cools off from sitting for awhile that it will idle at about 1500 rpm upon initial start up. Normally it idles around 500 rpm. Is this a way for the engine to heat up faster and a common occurence or something else? Thanks.

 

Warm up mode most likely. How cold is it outside? Also, if you have a lot of load on the alternator, the idle will compensate. On 06's the idles control and throttle are all electronic, so there is no way there is something wrong.

 

Ah ok, good to know. It's anywhere from the high 30's to mid 40's.

 

That's cold. It's normal. Warm up mode and cold weather + heater on probably.

Welcome to i-Club and stay warm.

 

All modern cars will have a faster idle at cold start-up, which is also weather dependent. Fast-idle in conjunction with richer mixture compensates for less efficient fuel atomization when the cylinders and cylinder heads are cold. Fuel has a greater tendency to drop out of the suspension in the air/fuel mixture and collect on cold intake manifold port surfaces.

Old cars would use a carburetor choke to accomplish the same fast-idle and rich mixture mode. As the cars aged, varnish deposits would sometimes gum up the works and prevent proper choke functioning - not very likely with today's computer-controlled fuel injection systems.

My '02 WRX shows much different cold-start characteristics in 40-degree weather compared with summertime conditions of 95+ degrees. It isn't that the engine fluids are fully warmed up in just a minute or two of running in 95+ degree ambient air temperatures, but those warm temps allow better atomization and the ECU gets out of cold-start mode sooner.

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Thanks a lot guys. I suppose it just wasn't as noticeable in my Durango