After completing a tuneup on my 1997 Outback, I noticed the engine occasionally increasing idle RPM especially when hot. The RPMs will stay in the 1500-2300 range with a 2000 being the average for a while. The fuel economy was also negatively impacted. For the tuneup, I replaced the ignition wires, spark plugs, fuel filter and air filter. For the ignition wires and spark plugs I used Bosch. I didn't have the tool that sets the gap so I just set it to the old spark plugs' gap. The old spark plugs were NGK. One mechanic advised me of Bosch spark plugs not being fully compatible with Subaru engines and suggested to use NGK instead. Some one else told me that it could be the wrongly set gap. Any help would be appreciated.

My first guess would be that a hose somewhere didn't get properly reconnected.

Do you mean an ignition wire? I checked and double-checked and re-connected all 4 of them.

No, sometimes a vacuum leak can cause a high idle. A hose related to the air cleaner or some other hose that may have been knocked off perhaps.

Oh, I did notice a whistle-like sound afterwards. I'll check them tomorrow. Can it also affect the fuel economy? Thanks.

and leaving off a hose is something we have all done. A hose can also get cracked if it is old and you move it.

Heh...My car would start and immediately shut off, over and over again, after I had replaced the O2 sensor. WOULD NOT stay started. I realized that as I was finagling around to get a good angle on the wrench while loosening the sensor, I had completely disconnected a vacuum hose.

I noticed that the air filter cover was a bit loose and put it back in place. However, that did not fix the problem. Could it be a bad sensor?

 

 

 

No, sometimes a vacuum leak can cause a high idle. A hose related to the air cleaner or some other hose that may have been knocked off perhaps.

PCV filter?

I'm going to side with 99obw for the moment.

 

I have the same car. Take a good look on the underside of the ducting between the air filter and the torque box. There are some vacuum hoses in there (one quite large in diameter) that are nearly impossible to see from any angle. Trace every single one.

 

It has been reported by many that Bosch plugs don't work well in Subarus. Some seem to have luck, but many have not. And if the gap is off, it could just aggrevate things.

 

Commuter