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Discussion Starter #1
I was previously throwing a code for the bank 2 O2s, which I figured was the bad cats and the oil that had gotten in the exhaust due to stuck valves when I first got the car.

I recently had new 2.5" mandrel exhaust put on along with new high flow cats and while it was being done a whole new set of Motorcraft O2s. Following that, I went through and replaced the list of rubber vacuum lines on the 1997 4.6. The air intake box, MAF and throttle body were inspected too.
I reset the computer and haven't really driven it far yet, just a couple blocks a few times.

Issues:
It smells like the car is running slightly rich.
Once the car is up to temp, it idles fine in park (800-1000 rpm) but stutters hard and will occasionally die when you put it in gear. If it does stay running it settles at 500 rpm.
The car does not miss a beat once moving and responds quite well to the accelerator.

I didn't think the car would need tuned after this work. Is it something I should let ride until the computer gets re-acclimated to the new emissions or are there some other things to look at?
 

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You said you inspected the throttle body. Does that include an examination of the IAC valve? If not, and it's not a new one or recently cleaned one, you might want to pull it, spray it down with carb/choke cleaner, make sure the piston moves smoothly and reinstall.

The IAC is moot at open throttle (once moving), as its function is to control airflow with the throttle closed (idle), bypassing the throttle plate.

A sticking IAC valve generally doesn't cause a DTC, in my experience. It's just one of those things you have to consider as a potential culprit, like vac lines.

edit: Incidentally, some people will say to soak the IAC in gasoline or other various things to clean it with, because (they say) carb cleaner will eat the insulation off the IAC's motor windings. I can't say I've had that happen to me, but then again, I likely didn't drown the thing in cleaner and dried it out soon after it was verified operational. YMMV with carb/choke cleaner; use at your own risk.

more edit/addendum: If you have a live data scanner, take a look at your TPS and make sure it's within range and it gives a smooth transition from idle to just barely above idle. If you don't have a live data scanner, you can do a resistance check at the TPS terminals with a DMM (analog is much better for seeing rapid transition events (such as with dirty pots); an analog bar graph on a DMM will do).
 

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Check for coolant leaking into the spark plug wells.
 

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Discussion Starter #4
I had replaced the EGR not to long ago, but I forgot about the IAC, I'll check it out.
As for the plug wells, they look nice n dry.
 

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I had replaced the EGR not to long ago, but I forgot about the IAC, I'll check it out.
As for the plug wells, they look nice n dry.
Did you actually remove the wires and check or just look. If you just looked at it them I strongly suggest a second look by removing them and making sure the boots are clean and dry.
 

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Did you actually remove the wires and check or just look. If you just looked at it them I strongly suggest a second look by removing them and making sure the boots are clean and dry.
I'm not the OP but I found a light coat of oil on boot #4. The plug well was dry. Is this a bad sign?
 

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I'd think plug hole/boot contamination would cause issues at open throttle as well -- as indeed mine was doing due to coolant on the boot and in the plug hole.

He said his car runs fine at all but idle.
 

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Discussion Starter #8
I did a second look at the plug wells and pulled all of them, they were all fine.
I also pulled the IAC and cleaned it as mentioned, that seemed to help the idle which now settles about 700rpm.
I'm still getting a rich smell from the exhaust.
Could a restriction caused by build-up in the EGR tube cause this? The valve itself is basically new and I cleaned what I could from the top side of the tube...
 

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You said you inspected the MAF but did you clean it as well?
 

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Yes, do make sure the MAF is spotless.

Also make sure the cleaner element is clean and breathing well. Are you using an aftermarket performance filter in your stock box, such as the FRAM Air Hog? You have to keep those things cleaned and re-lubed with the proper oil or suffer the consequences.

As for the MAF, I spray mine with mild and no-residue electrical contact cleaner. It works well and hasn't attacked the bobbins or wires yet, after numerous cleanings over the years. Do not use standard degreaser sprays, which some electrical contact cleaners qualify as.

If I've neglected it, I have to go over it 2 or 3 times -- I check my MAF under 8x magnification and usually find tiny specks of dirt left after only 1 or 2 shots of cleaner spray. Like I said, it's mild cleaner and the gunk is stuck really well sometimes.
Speaking of neglect, an oil-based air filter can lead to more frequent contamination of the MAF than dry paper filters (especially if the latter is replaced on schedule). It's even worse if you don't apply the correct amount of oil.

If you have a steady hand and can be gentle, you can use iso alcohol (recommend 91%) and a cotton swab on the MAF. The wires are super thin and, although seemingly protected by a thin film of clear material (poly? epoxy?), don't be the slightest bit aggressive; let the weight of the swab do the work and rake it gently across the bobbins in the direction of the windings not across them and stay away from the welds at the support posts.

There's also special spray cleaner designed just for MAF's, if you feel like dumping $5 or more on a small can.

All that said, however, my car tends to run lean when my MAF gets dirty and I notice issues at open throttle.

Do you have a live data scanner or just one that reads DTC codes?
With a live data reader, you can monitor fuel trim trends. If you can post trim numbers here, it might help rule some things out.
 

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Discussion Starter #11
Update:
Checked and cleaned the MAF.
The CEL came back on and gave me a code that I hadn't gotten before, for the cam position sensor. This would lend itself to what I'm experiencing along with all 4 O2s reading rich. So guess I'll go for the obvious.
 

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Check the fuel pressure regulator. If the diaphragm ruptures then your engine would be consuming unmetered fuel which would explain the rough idle and rich codes. Pull the vacuum hose off of it while it's running an it should not be wet. No fuel should come out of that.
 

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ok the first thing is first.

If you have o2 issues on bank 2 remember replace all four to make sure your nor going to be replacing bank one side.

the other thing I will check is the iac and the gasket because when I got a bigger throttle body and upper plenum for my mustang I messed up the gasket it was doing the same thing.

I sprayed carb cleaner in the Iac and put on a new gasket for it.

it sounds like you might be getting a little more air some where at the iac or around the breather box tube that connects to it.
 
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