I have an 03 sable LS with the 3.0L DOHC engine. I have a little stumble at times at idle. When you hit the throttle more than a snap, it also stumbles. It stalled on me once when I pulled out of my parking space but only once. This is my first Ford/Mercury machine so I was wondering if there is anyone who had a similar issue. I ruled out intake gaskets and vacuum leaks, as I sprayed all around with carb cleaner and the idle didn't change. I cleaned the throttle body and IAC. The dude I bought it from said he just did the plugs and wires. I sprayed the coil with water with no arching evident. Fuel pressure is between 35 and 45 psi. The code stays pending and does not set the CEL. Any thoughts? It has approx. 82,500 miles...

 

The P0300 code is an occasional misfire which even you have detected at idle. Could be something as minor as a vacuum hose leak although it sounds like you have checked for that, up to something like a sticking engine valve. It is hard to pin down when it only does it occasionally. I have heard of some Ford Ranger 3.0 engine having a valve problem.

Seeing how you have covered the other bases, I would suspect a valve problem.

 

My car has had similar symptoms, but without the code. I know you said you've checked your coil pack, well, have you removed it so that you can see the bottom. A hair-line crack in the epoxy can cause this. In fact, I've gone through several on my car. They mounted the coil packs right over the right hand exhaust manifold and they get very hot; which I believe causes them to fail prematurely. On my car, I replaced the coil and made a heat shield and placed it between the coil and the manifold to direct some of the heat away from it - this seems to have helped.

 

I physically checked the coil. It did have a hairline fracture in the epoxy, about a half an inch. I sprayed it but it didn't change the idle. Could this little fracture be an issue? I also checked the front three plugs. They were gapped at .045. They'r supposed to be .052-.056. The plugs were autolite double platinums. Everyone tells me to replace the autolites with motorcrafts. Maybe I should. By the way, the starter took a **** and I had to replace it...

 

If you have a crack in the opoxy, even a hair line crack, it will cause this problem. Get a new coil pack and I bet your problem will go away. I also strongly recommend making a heat shield. A simple piece of lightweight sheet metal or galvanized metal bent up on the firewall side will divert the heat. Don't bend it down because that will only draw the heat in. I also used a thin piece of rubber between the coil and the heat shield. Drill some holes in the heat shield/rubber wear the coil pack mounting screws will pass through and mount it to the valve cover in the original holes.
As far as the spark plugs go; If they appear to be in good shape, there is no reason to throw them away. Regap them and reuse them, if you want to. If they're very old, I would probably replace them (simply because they're so hard to get to). Also, while you're there, ohm out your spark plug wires. Good wires ohm out at around 5-7K ohms per foot. If your seeing 10K ohms per foot, then you need to replace them. Spark plugs and a new set of wires (with a lifetime warranty) are not that expensive and well worth the investment.

 

I got the coil pack on order, Monday, Tuesday-ish. I'll let you know what happens...

 

I put the coil pack in. It still has a little stumble. Fuel pressure is good, no codes, nothing. I'll check the wires and back three plugs next I guess...

 

The job sucks on these cars don't it!

 

The CEL finally came on but with an unusual code: P1633-Keep alive power voltage too low. It has to do with the keep alive power. Then my wife said she turned on the AC and the car really started to stumble big time, to the point where she couldn't move forward. Then she turned off the AC and the "normal" little stumble returned. Any thoughts? This might be one for the dealer...

 

This sounds similiar to a problem I had on my Explorer. My wife and I drove out of town and back again ending up at a resteraunt and ate supper. Afterwards, when I tried to start the engine, everything went crazy! The power door locks started going up and down; the interior and dash lights were flashing on and off; the stereo was turning on and off; etc.! I didn't know what to think. I had it towed home just to find that the only problem was a very weak battery. The multiplex circuit in these new cars can make them do all sorts of weard things.

Check the battery by giving it a load test and also check your alternator (or have it checked at your local auto parts store). Sheesh! I sure hope this fixes it for you.