I have a 2002 Forester with 192,000 miles. It has a manual transmission. I currently have the p0420 code in it. It comes and goes. The problem I've noticed, and has been progressively worse, is that the steering wheel shakes really bad starting at around 50mph. It also pulls to one side when I let go of the wheel. When I put it in neutral, it doesn't coast for long. It brakes on its own. It also loses pickup. It's as if the brake is on. The weird thing is, at times, it simply doesnt shake. It runs smooth as butter and it doesn't pull to one side when I let go of the wheel. It pretty much drives excellent, like new! I'm perplexed. Can someone assist, please.

Welcome to the board. Might be your caliper intermittently locking up or sticking causing the brake pads to hit the rotor over heating it thus warping it. Also check struts, tie rod ends, and ball joints.

Thanks. Is there a particular way to check some of those things. I visually inspected them, but I couldn't see anything unusual. I'm assuming if the caliper sticks, it could be a master cylinder issue?

Check out videos on youtube on how to check front suspension parts and how to check caliper.

 Caliper sticking is either the caliper itself or the rubber line that goes from the body to the caliper. The line is hard to diagnose because it is usually an internal collapse of the hose.  Both caliper and the hose are pretty cheap on Rock auto.  If you find its the caliper or hose you might as well replace the hoses, calipers, rotors  and brake pads on both sides and do a fluid flush while your at it.

you could carefully compare temps of the hubs and rotors after a highway run. Best to use an infrared therm but touching quickly may work OK. Only a coupla things would heat-up one hub more than the others, bad wheel bearing or dragging caliper. Most likely front wheel (on side toward the 'pulling'). Less likely rear wheel.

 

 

http://www.amazon.com/Etekcity-Lasergrip-Temperature-Non-contact-Thermometer/dp/B00DMI632G/ref=sr_1_3?s=hi&ie=UTF8&qid=1432699881&sr=1-3&keywords=infrared+thermometer

Edited May 27, 201510 yr by 1 Lucky Texan

Temping is probably the easiest was to check.  There should be discoloration on the one that get's hot. Most likely the side it pulls to. I wouldn't actually touch it, as if it is sticking, it could easily be a few hundred degrees. But, you should have an idea by putting you're hand close to it. Probably can feel a difference in the wheel as well.