Rough idling

I have a 2003 Ford Taurus SES, 3.0L Duratec DOHC. It's running really rough. Started out just a slight hesitation upon accelerating, in less than a week, it began to miss. Replaced plugs, wires, coil pack, didn't fix the issue. It idles really hard and occasionally makes a loud popping noise like a backfire noise, under the hood. There's also a slight hissing noise, so I was thinking maybe a vacuum leak, but I can't find one. Took the IAC off, checked it out and cleaned it, put it back on the car and still had the same problem. I've thought, PCV, EGR, MAF. But I have no idea. If anyone has had similar problems and figured it out, PLEASE let me know.

Also, it's been running like this for a couple of months, but recently got so bad we had to park it. The problem with diagnosing this issue is that the check engine light has only appeared intermittently and doesn't stay on long. Took it to O'Reillys and had them check it and the codes it threw were po300, po301 and po316.

. Fast forward a bit.I've now replaced the PCV Valve and it seems to be running much more smoothly. BUT, now I hear an exhaust noise I didn't hear before. Out of the tailpipe comes a noise that sort of sounds like a muffled outboard motor. Recreating the noise via text, the closest I can come is "blub blub blub blub blub". Could this be the catalytic converter?

Replaced the pcv valve and it is idling way better. I do believe there may've been a vacuum hose that was loose, but as we took the whole dang car apart to get to the pcv valve, when we put everything back on, we made sure all the hoses were snug.

Now we have a problem we didn't notice before, obviously because it was making so much noise while idling. An exhaust noise. While standing at the rear by the tailpipe we hear a "blub blub blub blub". Could this be the catalytic converter?

Okay, replaced the camshaft sensor now, as that was one of the codes it had thrown in the past. Car still runs like a pile of crap. What a shocker. Anyway, upon looking down below the left side of the engine (which would be in the back under the hood, since the front of the engine is on the passenger side.) We can see that the exhaust manifold is glowing bright red after the car runs for about 5 minutes. Now we're certain this catalytic converter needs replaced, but we fear that this is a symptom of something else that we haven't been able to diagnose and repair.
Any suggestions? Getting the cats replaced is going to be big money, I sure don't wanna get it done, then turn around and have to do it again after we finally figure out what's wrong with it (other than it's a taurus. Sorry, just not a fan of Taurus'. Wonder why?)
I would put a video of what it's doing, but I don't think I can on this site. Perhaps upload one to Youtube.I'll post link here if I do.

Only when the a/c is on - my Taurus idles rough. Turn the a/c off and it idles smoothly. No other problems

Valve seats. Common issue on these motors. Do a compression/ leak down test to confrim. Just repaired another one of these this week. Good luck.

I have a 2003 Ford Taurus that at various times starts idleing rough and dies. This happens quite often and starts up again soon after. It has been put on a diagnostic machine and nothing shows up. It has happened on highways and city roads. It's like being in a death trap. Any answers?

Three days ago it started running rough during cold startup then then runs great when it warms. Has not stalled just idled rough so far.

It has been idling funny like it is misfiring. I replaced the Idle air control valve. Runs a lot better when driving. But in park it runs choppy as if it has a lope to the exhaust like if it has aftermarket cams in it. So I cleaned the TPS, MAF, and checked for vacuum leaks with throttle body cleaner. Nothing.

The only thing I can think of would be a cam shaft position sensor, crank shaft position sensor, a bad injector, or plugs. But no check engine light has came on or anything.

So no lights, no codes, what else could it be?

Hi,
my care has been idling rough when I come to a stop at a red light. It will usually go completely dead at a stop unless I put it in park. I put in some fuel treatment but this has not helped. Please let me know what you think the problem may be. Also, my check engine light is on.

Thank you,

Ashley

When at first start from a cold engine, as soos as I place the shifter on drive or reverse, a rough idle occurs. When I return the shifter to neutral or park, it's smooth idle. No trouble codes. Had the trasmission oil replaced and same problem.