running rough and poor fuel milage

[dusterbd13]

over the past few months, my car has been getting worse. 2002 legacy 2.5 gt.

its running pretty rough at idle. to the point that i cant use the rearview at a stoplight. never cuts out, idles at about 650-750 RPM.

its down to 17-18 MPG on trips that we used to get 22-25.

it has no power.

it sets the CEL for p1402 (cat converter effeciency)

it also sounds like it has a valvetrain tick.

i have put seafoam through it, changed brands of gas, replaced plugs, fuel filter, and air filter.

monday i have the day off. so im planning on pulling the valve covers for a valvtrain inspectiona and adjustment. while i have it on the lift, im also planning on dropping the cat to check and see if its stopped up. if it is, can i gut it and use the spark plug nonfouler trick to keep the CEL at bay? it has to pass inspection in a couple of months, and in NC it wont pass if the CEL is on.

anything else i should check? im also planning on cleaning grounds and checking the TPS sensor.

any other ideas?

Michael

[Grafton]

one way to tell if the cat is acting up is if it's getting really hot, after you go for a drive pop the hood and you should feel the heat coming off of it if its getting really warm

[ouch1011]

A cat converter will always get hot, they are designed to operate around 700-1000*F. If it gets hot enough to glow, which would be somewhere around 1600*F, that would be a problem.

If the car is running poorly, I'd say the cat efficiency code is false. Whatever is causing the engine to run poorly is causing excessive emissions, which is causing the cat code.

If it idles rough, see if you can identify which cylinder or cylinders are misfiring. With the engine running, pull each of the spark plug wires away from the spark plug briefly (don't pull it at the coil unless you want to get shocked). You can also do this by unplugging each fuel injector individually, whichever you would rather do. If you disable the cylinder and the engine speed barely drops or doesn't drop at all, you have identified the misfiring cyl. If none of the cyl is misfiring, you probably have a bad sensor somewhere that is affecting the air/fuel mixture.

[legacy98gt]

the guy at the muffler shop told me that if the cat turns purpleit is no good, not sure if it is true or not just wat he told me.

[ouch1011]

A discolored cat is can be a sign it has gotten very hot. But again, that is a very vague, "backyard" kind of diagnostic. There is the potential to get a cat hot enough to discolor a bit just from driving really hard for an extended period, say pulling a lot of weight up a long, steep grade, or doing a top speed run or something.

[dusterbd13]

the rough idle is only in gear after the car gets warm.

so, most likely causes? i have an FSM and a nulti meter, so im planning on checking sensors as i can.

[jey]

Yes, I'd test the O2 sensors first!

[ouch1011]

If it only runs rough at hot idle, I'd say a bad plug wire or vacuum leak.

Anyway, what did you find? Also, how many miles on this car?