CEL: Misfire Cyl 4, Evap Code. Also Power Brakes Went...

I have a 2001 stock automatic XJ 4.0 4X4 with 182k miles. Got it recently. It threw a CEL so I got it pulled at Pep Boys. They said it was Cyl 4 misfire and slight evap leak. So I replaced the gas cap with one from the dealer and hoped the misfire was random. Well about 140 miles later the CEL came back. Again, same thing, Cyl 4 misfire and slight evap leak. So I got it cleared again, and again it came back about a hundred miles later. All of this has been going on for maybe 600-700 miles, and this weekend my power brake booster stopped working. My question is, is it possible these problems are linked? Could there be some sort of vacuum leak leading to the evap code and the power brakes going out? Not sure why cylinder 4 is throwing a misfire at the same time... Or do I have two separate issues -- the misfire/evap code, and the power brakes going out. I don't want to replace the power brake booster if there could be a vacuum leak... I checked my vacuum connections and they seemed solid at a glance. I would also note the car is running pretty well. Usually idles around a grand or a little less, sometimes a little rough when cold but not usually. Car also drives very well.

thats a higher than normal idle. probably a vacuum leak. i would start by replacing the sparkplugs.

So is your pedal rock hard even with the car running?

I'm thinking you have 3 separate problems going on here.

Misfire- have you done a full tune up recently?

Evap leak- Like looking for a needle in a hay stack...Check ALL your evap line from engine to gas tank. I found mine with a smoke machine....oh those are sooooo nice.

Good news! Found a vacuum leak coming from the intake to the power brake booster. I looked before but couldn't find it. I could hear it bad though with the engine on (checked connections by eyesight before with the engine off, bonehead move). The plastic valve on the power brake booster was broken. So I called the Tustin Jeep dealer and they said their Irvine store had one. So I drove down there to get it, and they did NOT have it :gonnablow. They also wanted $25. So I went to Autozone, and they had a universal Chrysler/GM valve for $6! Now I have power brakes! So, I am resetting the CEL and we will see if it comes back. I am guessing the misfire will come back, but not the evap...

As for a tune up, the previous owner replaced a bunch of stuff, however he was a bit of a flake when it came to actual records (though I believe him, even in this day and age). Supposedly he did the radiator, some various seals... I'm not exactly sure what he did. If the CEL comes back, I'm going to replace the plugs.

Good new about the brake booster check valve.

Although I believe your evap code might return...VERY common thing.

Misfire could be intermittent and go away with a tune up.

Not much to a tuneup with the 00-01 that have the distributorless ignition. Install new plugs. From my experiences with this ignition, the NGK is a very good choice.

Not a bad idea to toss in a bottle of QUALITY fuel system cleaner in a tank of gas (BG44K, Techron, etc). Can help optimize fuel injector spray pattern. Stay away from the $2.00 a bottle stuff that lines the parts store shelves. Pretty ineffective.

If this misfire continues, you could try swapping the #4 injector to a different cylinder to see if the misfire follows.

For the evap code, start with a comprehensive search of all vacuum components around evap. hardware. And as mentioned, if you get stuck on this one, a shop that can perform a "smoke test" would be able to find it.