the other day, the car acted like the knock sensor activated- wouldn't go over 3000 rpm's. I filled up with super unleaded and added an octane booster just to be sure, and then the car revved like it should.

But, the check engine light didn't turn off.

So, i had the codes read, and here's what I got:
P0300 random misfire
P0301 misfire cylinder 1
P0302 misfire cylinder 2
P0303 misfire cylinder 3
P0305 misfire cylinder 5

P0174 fuel trim bank two


I had the plugs replaced about 4000 miles ago, car has 147,000 miles, is driven daily.

It's odd that I would have so many misfirings pop up all at the same time, especially since Mr Lucas has been banished to the seventh level of hell where he belongs , so I'm wondering if something else is going on here.

other than a few occasional lags at idle, the car acts fine.

has anyone run in to this before?

 

Classic symptoms of a vacuum leak somewhere.

It threw you in to "Limp Mode", probably until you stopped and then restarted the car. Vacuum leaks seem to always play havoc with throwing weird, untrue/unfounded hard codes, too.

Go to the X-Type Forum page, and poke down the page a bit for the thread "Help with mechanical issues??". Read the fourth reply in there, the one by Thermo.

Good 'ol Thermo has the instructions for finding the leak down to a short, easy to understand exercise.

When you find the leak, a wad of chewing gum or duct tape will probably suffice to fix it until you get the new needed part. Down and dirty, cheap and easy.

All those codes kind of send a chill up your spine, don't they?

One that stops right at the bottom of your wallet.

Just clear the codes. The Check Engine Light will turn off, and you'll be fine until the engine swallows a little too much air again from the vacuum leak and pops back into Limp Mode.

Scary as it probably seems, your problem is not a problem, but more just an inexpensive inconvenience. Duct Tape and Gum can last thousands of miles, too - once you find the leak!



(Ain't that just a beautiful repair job?)

 

Tumble, I would say to first start with the big 3 vacuum leakers (PCV hose, brake booster hose, IMT valve o-rings). The PCV hose is easy to determine (which I would venture to guess is your problem based on the codes you are seeing). If you look on the underside of the hose, it will split there and is easy to replace. You can then look at the brake booster line and see if the "football" (bulge in the center of the line) has a crack in it or is starting to turn to dust. If in doubt, replace.

WIth the IMT valve o-rings, you can either use a little bit of starting fluid sprayed over the joints (if the RPMs pick up, there is your leak) or you can take a short piece of tubing and place one end near your ear as you run the other end near every joint of the intake. If you hear a sucking sound, there is your vacuum leak.

If you need any more help, let us know.

 

I would be willing to bet that my mechanic reused the O-rings when he did my spark plugs, so I'll do the starting fluid trick and see if that's the case....

 

I finally got around to looking at this... I bought some starting fluid and sprayed it at all of the intake manifold to cylinder head joints, no change in RPM.

None of the hoses look bad.

where is the PCV hose?


and... is there an easy way to clear out the codes?

 

Have a look in the S-Type forum about LTFT, checking with OBD, elm327 and so on.

 

TUmbleweed, the PCV hose is easy to spot. First off, remove the cover over the engine. Now, find the 4" hose running between the intake box and the throttlebody. Now, look a little to the left of the intake hose (4" hose) and you will spot a 1" hose running from the front valve cover back to the intake. THis is the PCV hose I am talking about. Disconnect 1 end of the hose and then look at the underside. Do you see a split there? This will be more common if you have the smooth hose vice the ribbed hose (if in doubt, you have the smooth hose). ANy sort of split in the hose, replace it.

 

I just finished replacing all of the spark plugs in my '02 X-Type. I replaced the intake O-rings along with all of the coolant hoses while I was in. This was part of the normal oil, filters, etc. When I started it up I could swear I heard a deeper air sound than normal and then the rough running started and sure enough error codes. P0301, P0302, P0303. Nice, cylinder 1,2,3. I looked everywhere and could not find anything amiss. After reading the thread on the PVC, brake booster hose, vacuum related items, I went right out with the plan to use what I learned when flying. If something isn't right and you "think" you have looked everywhere, touch every instrument in the cockpit and take a good look; sometimes you are seeing what you want, not what is true. I started with the PVC hose and started touching every vacuum hose under the hood. When I got around to the back of the intake manifold there was a capped hose about 2/3rds of the way to the right on the back. It appeared to be attached to the intake but when I touched it...the metal nib from the manifold was underneath the hose end cap and detached! I could not see it from the position in which the hose was resting after I put the intake back on. I pushed it on and started her up. She is back purring. Thanks for the focus on vacuum to get me headed in the correct direction.