I picked up a 2005 Impreza from a coworker and it's going to my brother's better half.

 

Auto

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Runs nice, but has a low idle, showing 300 RPM on the gauge in D or N. 

I plan on running some Seafoam through it

Changing the Plugs and see what they look like

I've added some lucas fuel conditioner and Shell premium

 

Idle control valve?

 

I'm just starting on this one

Thanks, Larry

First, stop adding snake oils hoping it'll magically fix itself. You've been here long enough to know you should do a full tune-up (oil, plugs, wires, fuel filter, air filter, run a tank of premium through it in case gas is old, and reset the battery in case it's had work done, and inspect all vacuum lines). IF after all that it's not running right, then start digging into the idle air valve, etc. What exactly do you think sea foam is going to do to a healthy engine anyways? Other than possibly ruin it? Only non-mechanic types resort to snake oil. 

Lucas Injector Cleaner is snake oil? 

I use that stuff religiously because it just plain works. 

 

I use Seafoam all the time as well. Does wonders for rough idle and hard starts. You just cant be an idiot and try to dump the whole bottle in all at once. 

 

If that car has electronic throttle control it could be in need of a throttle body cleaning. 

Yep, I've had good results with both if used correctly.  And yes, as I said a tune up is on the schedule as well as a good inspection the engine.