Diagnosis - P0171 and rough idle

I'd like to share a recent experience with my 2003 ES (close enough to P5 to post here). I took it in to the dealer for the recall on the VICS screws and when it came back, I kept getting P0171 CELs.

First instinct was vacuum leak related to the VICS work, and I haven't called the dealer on it, yet.

Second instinct was O2 sensor. I may have gotten some air tool oil on it while trying to get the threads lubed before installing my header. I tried to clean it with fast evaporating cleaner, like brakleen (spelling?) and sprayed the electrical connector with electronics cleaner. Voltages look the same as before, but you can't tell with the oscillation.

CEL happens less frequently now, but I got one for P0455 (which I attributed to a gas cap being loose, we'll see if it happens again) and this morning I had a low idle that wasn't normal. Doing some research on the EGR clean related to rough idle I had a thought. What if the EGR is causing a low idle due to carbon buildup, and what if it's doing that because it's stuck slightly open? That would explain the lean CEL. I wonder though, if that would typically trigger a "high egr flow" CEL at the same time. Maybe not, because it's typically open at non-idle conditions.

I'm going to clean out the EGR and IAC and see what happens. If the O2 is good, and the EGR is fine, I'll probably call the dealer back about a vacuum leak.

Any suggestions, comments, opinions would be appreciated.

Thanks.

Oh, and there are some good resources on this site:
http://www.aa1car.com/library/emis2p.htm

So I took off the throttle body (TB) to clean out the EGR. There's a loose vacuum line that goes to the TB. Stupid dealer techs...

I continued to clean out the EGR and throttle body. It's amazing how much gunk is in there that looks like unburnt oil. Anyways, cleaned out the gunk, put it back together.

I messed with the throttle position sensor (TPS). When I put it back together I noticed that it was adjustable, and I didn't mark it when I removed it. I centered it and tightened it down. Unfortunately, the car drops idle to 500 RPM and immediately recovers, for about the first 30 minutes of driving when stopped. I don't know if it's because I cleaned out the EGR, or the TPS, but I'll take a look at the TPS position when I get a chance.

So the vacuum leak was the culprit, easy fix.

Good catch. Asshat dealers never care about anything beyond the sale. ALWAYS check up after them IF you HAVE to have them do anything to your car. FYI, the IAC valve on throttle body can also affect idle if dirty with carbon too.

I'm not sure what the deal is. There are a lot of hoses to connect, but I did it right the first time I took apart the manifold.

I couldn't get 2 of the screws out. I used a tiny pipe wrench on the screws to break them loose, but it wouldn't fit on 2 of them. I couldn't get the screws loose without the chance of stripping them out.

which idle screw did you adjust?