OK, I read a lot of the threads about rough idle, but most of those dealt with intermittent roughness. Mine is constant. No SES/CEL lights. Listening with the bonnet open, I hear what sounds like exhaust noise (like you were standing at the back of the car, hearing the tailpipes) coming from the manifold area. If I had a leaky manifold gasket (or similar) would that throw a code?
I don't recall this roughness being present when I got the car 7 weeks ago. I have put 6k miles on it (long commute) and in that time I have used Lucas injector cleaner once (right after purchase, as a precautionary measure), and Lucas octane booster once, after being stuck putting 89 in it. Car currently has 46k miles.
I'm thinking of running some Seafoam through the fuel system, but this is just a desperate attempt at a cure.
Any thoughts?

 

Probe around the engine bay with a length of hose (1/4-3/8 ID.) held to your ear of choice. You should be able to locate the source that way. Let us know what you find.

 

I had a similar problem, after market wires were bad, check wires for loose connection or even a bad plug,

 

No Headers,right? I don't see how a exhaust leak at the manifold could cause the engine to run bad. If the leak were bad enough to effect the O2 sensor readings you would get a SES/CEL and yourECU would run in limp home mode.
Had this once with a vacume leak at the BP valve. I had no codes or SES.

 

No header. All stock, except for CAI. Problem pre-dates CAI.
I did change the plugs about 5 weeks ago, but wouldn't a plug misfire trigger a code?
ECU was just updated a couple of weeks ago, so I'm pretty sure I have the current software version.

Valve (or valves) not sealing properly? That's kinda why I was thinking about the Seafoam.

 

I had a problem like that. Turns out my exhaust was just loose on the cat and it was hitting the heat shield. Made the car sound like it was idleing rough.

 

If you did not replace your plugs with OEM, I would recommend checking the torque on the plugs. Many people have reported plugs coming loose, especially #2 for some reason. An exhaust leak will not cause the engine to idle rough. What you describe is most likely an ignition or fuel problem. My money goes on a bad plug, wire or rotor cap. You can get a mechanic's stethescope at most auto parts places for not much $. It should be easy to diagnose where the noise is coming from with the stethescope. Hint... don't put it too close to the spark plugs or wiring, if there is a spark leak, you could be in for an unpleasant surprise

 

A stethescope works well for noisy bearings & tapping noises, but not vacuum or exhaust leaks. If it was a spark plug backing out it will be a tock-tock-tock sound. No rough idle or codes.

 

OK, been out checking on all of the stuff mentioned here.
namwob, I used the cheater stethoscope method you mentioned, and the only thing I could hear (possibly) out of the ordinary is a hissing/sucking sound around the I/C outlet boot. Sorry Tom, didn't want to chance frying what few brain cells I have left .
Checked all of the plugs, gutentite.
Had one heck of a time getting the car running! Did the usual cold start stumble and died. Re-started and it kept wanting to bog/ die every time I tried giving it some gas. Never done that before! Let it warm up a bit at idle and the bog sort of went away. Ran some errands (stopped off at A-zone and picked up some Seafoam), then got it out on the freeway and ran it up through the gears, shifting at 6k. Seems to have settled out. Maybe just needed to warm up a little. Rough idle still there, though.
Vacuum leak?

 

Thats what I thaught,still do. It won't be a large vacume leak or it would throw a SES. I think we can rule out crappy fuel if you have been going to a station doing lots of business, no water in gas. Wouldn't be a bad idea to throw in a can of Techron in the tank to disperse any water that may have accumulated there

 

Another thing, have you checked your engine mounts for leaks. A flat one could mimic a rough engine idle as the vibration would trasmit easier.

 

miminut,
Thanks for the reply. I always use Chevron (w/Techron!), so unless the station changed mixes, I should be good. Checked the motor mounts, all looks good.
The bogging issue today really has me baffled. Never done that before. Maybe I didn't get a plug wire re-seated properly after checking the plugs?
Went back and checked all of the wires and all are attached properly.
The hissing noise at the I/C outlet: would a leaky boot cause the problems outlined?
Sign me,
Confused