aprok

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?

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

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

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.