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Rough idle

My windstar 3.8 engine has idle problems and engine light comes on at times. Code po305 (misfire #5). When I add sea-form to tank and drive awhile, the engine light goes out and the engine idle’s normal. Is this a eva problem and what should I look for?

That code indicates a misfire condition in cylinder #5.
The way to resolve the problem could be as simple as replacing the spark plugs.
For how many miles have those plugs been in place?

If the plugs are not the culprit, then my next suspect would be the coil pack for that cylinder, but other possible causes of the problem include a bad fuel injector, or even low compression in that cylinder.

thank’s for the info.

Since it only occurs on one cylinder, a process of swapping coils, plugs, injectors between known good cylinders with number 5 is a common way to determine the cause for this problem. If the problem goes to cylinder number 3 when you swap the coils on 3 and 5, you know its a coil problem.

great idea!!!

@VDCdriver asked about the plugs. How old are they? Old plugs can kill coils.

Less than 3,000 miles on plugs

If adding the Seafoam causes the Check Engine light to turn off, and the idle to smooth out then the problem isn’t with the plug or coil.

The Seafoam wouldn’t have an effect on those components.

But it would have an effect on the fuel injector on #5 cylinder.

If the pintle on the fuel injector is sticking, the oil and solvent in the Seafoam may be freeing it up allowing it to work properly.

Before going thru swapping coils/plugs/injectors, try a few more tank-fulls with Seafoam added to see if the problem goes away.


i will

My feeling is that compression should always be tested when an engine performance issue exists.
It helps to weed out the possibility of a mechanical fault; especially since some of the 3.8 engines were known to have a head gasket issue now and then.

Some major disgruntlement can occur when someone throws a small fortune in parts at a compression problem only to discover it’s never going to get any better without engine work.
At least with compression known to be good one can breathe a little easier and know they’re not working with scrap metal.

I drive a 2002 Taurus with 128,000 miles on it. It s not a great car and since I am a college student I don t have that much money to spend on it. The car idles rough when had the coded checked there was a misfire on cylinders 1 and 5. I replaced all the spark plugs since I had recently bought the car and wanted to be safe. The check engine light went off but soon returned and the rough idle is getting worse. Now after idling about 20 seconds you can feel an abrupt change in the idle and it gets rougher than before, the check engine light also starts to flash. then it is difficult to accelerate for the first few seconds then goes back to normal and the flashing stops. I recently saved up enough money to change the ignition coil and plug wires although I changed the plugs almost 2 months ago. I also ran sea foam engine cleaner through a whole tank of gas. The check engine light again went off but as soon as I idled for an extended period the problem started again. Could the plugs have gone bad because of the bad wires and need to be replaced again, if not what else could it be


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