1999 Subaru Outback Wagon. Newly replaced spark plugs & wires. My knuckles have healed enough to type now. Runs great. Good mileage on a recent 1,000 mile trip. But at idle (like a stop light) there is a "stumble" every now & then... not consistent. almost disappears totally in neutral... the idle speed is low but can't see the how to increase that.

later,

Peter

btw.... 2.5 liter engine.

When you say low idle, is it less than 750 RPM?  If working properly, the computer controls the idle speed and you can't change it.

 

You probably have a vacuum leak.  A possible spot is the crankcase breather below the throttle body; the hose cracks.  A telltale is a dirty spot there where the oil has come out the crack in the hose.

 

How many miles?  It probably wouldn't hurt to clean the injectors either.

hmmm. I'll look for a vacuum leak in the moring. Yes, less than 750 (closer to 700 RPM)... 189K on engine... I've used "the seafoam treatment" sucking through a vacuum hose...

in any event, I'm hoping for a minor vacuum leak.

later,

Peter

I only post this cause mine would die at idle and we try everything to fix it, new spark plugs, new spark plug wires, distributor, cleaned idle sensor, even a new computer. If you have a manual there appears to be a ghost with the computer and you  sometimes need to replace the neutral switch to fix that...

 

This post may have nothing to do with yours, just wanted to throw it in (in case you try everything like I did).

I had a similar problem with a 2.2 and after a while it got really bad, it ended up being a bad injector. Try injector cleaner for a few tanks of gas and see what happens.

700 rpm idle is considered normal.

Does this stumble happen when the AC is turned on?