Hi All,

 

My manual 2000 Subaru Legacy has recently started acting up while idling over the past two weeks. It idles at around 900-1000 rpm and intermittently shakes. The shaking has gradually become more frequent over the past weeks and the CEL came on about a week ago. Just today, it occasionally started idling at 2000 rpm and increasing the rpms (accelerating) without me pushing the gas (this was mostly happening while I was moving).

 

My assumptions after some research is that it is either the MAF or MAP sensor. I sprayed down the MAF sensor with MAF spray to no avail. I visually checked for leaks in the hose and sprayed the hoses down with carburetor cleaner to check for hoses and did not see any leaks or hear the engine rev. 

 

I just had the CEL codes checked today, and it came up with P0304: cylinder 4 misfire and P0113: intake air temperature sensor 1, circuit high input.

 

Would totally appreciate any help as I'd like to avoid another costly mechanic bill 

 

Thanks!

could be 2 different issues. Is there any correlation with temperature or moisture? any oil on the plug wire boots? At that age, you could have old plug wires that arc and cause misfiring, maybe correlated with dew or cool temps. Does the shaking, misfiring settle down as the engine warms up?

 

Leaking valve cover gaskets can cause misfiring too as oil gets on the plugs.

 

How old are the spark plugs?

 

Bad, corroded ground wires can cause issues. Or rodents can chew wires - in addition of course to the possibility of a bad temp sensor.

Edited February 28, 20188 yr by 1 Lucky Texan

Thanks for the ideas. I just replaced the plugs and wires and the problem seems to be fixed. The plugs did look pretty rough, especially 4 which was the one misfiring. I did notice some oil on one of the plug wire boots (I think it was 3). I bought a temperature sensor as well, but am going to hold off on replacing it unless things start acting up again.