ruff idle at idle only?

[KRNFIRE]

i own a 2003 gt it runs ruff at idle only ?
i replaced the plugs ,wires, ignition coil.
it still runs bad at idle.
any ideas
i also get a code po304 (missfire plug 4 )

[garyerrol]

I think the next thing I'd do is a compression check to see if you don't have low compression in the 4th cylinder.

[CREWZIN]

Welcome to the forum. If you pulled the code and it's telling you that there's a misfire on plug #4, then I would suggest your rough idle is caused by the wire or plug #4.

Number 4 is the one on the far right when you face the engine. I know your said you just changed the wires and plugs. Your going to have to check them again, make sure the gap is good on #4 and the wire is seated correctly on both the plug and coil side.

The wire could be broken inside the casing so switch it with one of the other wires of the same length from the other side of the coil and see if the code comes up a different number.

[KRNFIRE]

i switched the #1 and 4 wire the same code came up?

[KRNFIRE]

sorry i also checked the gap its at 50

[KRNFIRE]

my gt has about 87.000 miles on it.

[CREWZIN]

TSB (Tech Service Bulletin) from Chrysler changed the gap from .050in to .040in but that shouldn't cause your problem.

Wooops. Sorry. that Tech Bulletin was for an N/A cruiser not he GT.

[KRNFIRE]

how can you do a compression check when the plug are so deep in the valve cover ?
my tester has a 2' rubber hose on it but how can i get a good tight seal with it only hand tight ?
do you know what the proper psi is ?

[CREWZIN]

Found this on PT Do-it-Yourself.net .......

Compression should not be less than 689 kPa (100 psi) and not vary more than 25 percent from cylinder to cylinder. If one or more cylinders have abnormally low compression pressures, the compression test should be repeated. If the same cylinder or cylinders repeat an abnormally low reading on the second compression test, it could indicate the existence of a problem in the cylinder in question.

Low compression in one cylinder usually indicates a bad exhaust valve. Low compression in two adjacent cylinders typically means a bad head gasket. Low compression in all cylinders usually indicates that the rings and cylinders are worn and the engine needs to be overhauled.

If compression is low in one or more cylinders, you can isolate the problem to the valves or rings by squirting a little 30 weight motor oil into the cylinder through the spark plug hole and repeating the compression test. The oil temporarily seals the rings. If the compression readings are higher the second time around, it means the rings and/or cylinder is worn. No change in the compression readings would tell you the cylinder has a bad valve.

[Hooligan]

Carey, you are a wealth of info.