2003 Jaguar XJ8 120,000 miles

Car ran fine before. Then it sat for a week. When I started it, it ran incredibly rough and got the following codes
p0300 - multiple misfire
p0301 - misfire on one
p0304 - misfire on four
p1316 - misfire

Ideas lads?
Skipped timing?

 

Check your battery. My low battery causes the engine to run rough at idle. Charged it up and problem went away.

 

Battery is proper voltage.
I started it up about 5 more times, it was very hard starting at first, lots of sputtering, but now it's almost back to normal. I cleared codes and they have not come back. The engine seems to run smoothly when revved, but has a distinct and rhythmic vibration at idle that shakes the whole car subtly. Fuel trims are proper.

 

If your voltage is good, swap the misfire coils out, see if it moved cylinders. If it’s not your coils, here is a list of other possible causes

 

Bore wash?

 

definitely an option too.

 

It is no longer misfiring, just a rhythmic vibrating idle. Anything that could could misfires but quickly go away after the engine has run a while?

 

How many miles on the spark plugs?

 

Less than 15k miles on the spark plugs.
I think it's a vacuum leak because it smooths out when I raise idle. There's also a faint whistling sound in the engine bay. It seems that when I let the car sit for a week the seal dried out. As it warmed up, it stopped the leak for the most part. Will replace the intake manifold gaskets and then report back.
Can a bad vacuum leak cause misfires?

 

Yes. But look at fuel trims for help.

 

I would check the ignition coils physically before removing the intake manifold

 

old toyota and other brands using denso ecm have always had **** poor misfire detection. you get a lot of collateral misfire codes when it’s really only one cylinder.

if it was just on that cold start ignore and go do something better with your life

 

I have found that the coils on these cars tend to be the best place to start when diagnosing
misfires. Some have found oil deposits in the spark plug seating area and that is an issue
that may be of concern as well.