Any ideas??

Here are the codes, p0257 (turbo boost, sensor signal circuit problem)
p0171,( fuel trim sensor signal lean)
p0131 (p0131(Oxygen sensor signal is too lean)

My car is running pretty good while it's warm. When I first start the car it idles rough. On the highway it runs great. Once it's warm it idles ok.
Within the last 10K
new fuel pump, new MAF, TPS IAC, plugs, wires, injectors, alternator, PCM, Starter, replaced all vacuum lines, battery, belts, hoses, brakes, oxygen sensor,

Never a MIL on the highway only while it idles?
Any thoughts are appreciated.

How long ago did u change youre O2 sensor???
Which O2 sensor was it?

I put in the one before the catalytic converter, about 3,000 miles ago!

Sounds like it could be a MAF sensor or MAP sensor too... I'd look at a MAF first. Try a used one if you can find it cheap to rule it out.

Thanks Derek, I put my old MAF on and took it for a short drive. It had awful acceleration. Car runs a lot better with the new MAF. Cleaned and put the new one back on. I do appreciate the recommendation.

gonna take a stab in the dark here...since you've already replaced everything I might suggest... it just popped into my head... how about your exaust manifolds? Big hole blown in them *might* cause strange O2 issues....which in turn causes fuel issues.......

also as a note, there is no MAP sersor on the series one SC....

.. or try popping in a new PVC valve? would be a cheap thing to try... a working one should rattle....

You changed the fuel filter, right?

What is the fuel pressure reading @ idle and WOT?
As Aaron mentioned above, possible reduced fuel flow due to plugged fuel filter or bad fuel pressure regulator.

Yes i did change the fuel filter as soon as i got the car. I will check fuel pressure tomorrow. thanks for the input. It's running pretty good just the frickin idle bugs me!! I also thought about fuel pressure regulator. I saw the custom pressure gauge mount somebody did on here a couple of months ago. I will try that tomorrow after work.
Thanks again

If it was mine I'd have a GM dealer remove and clean the throttle body. Do it removed not on the car to get it really clean.

I'd also be looking for a wiring problem, like a bad connector/loose wire in a connector/wire broken inside insulation at one or another strain point.

I worked fourteen hours today so no time to test fuel pressure. Thanks albertj, I took the intake off and cleaned it real well about 3,000 miles ago. It was real bad. (Replaced gasket)
Wiring could definitely be a problem. My motor was changed out before I got the car. I wouldn't let the guys who did the motor swap work on my wheel barrel!!!
No MIL today and I drive 50 miles to and from work. It ran great, no Idle problems, average highway speed 80+mph. It doesn't make sense. I will try all suggestions and do appreciate the input. Just need to find the time.

I understand about the time.

If you have a moment poke around and see if something is just loose, like maybe a throttle body bolt or something, such that you might have an occasinoal air leak where there should not be one.

Almost wonder if you had water in the gas tank from accumulated condensation or an accidental tank load of bad gas.

Albertj

I really appreciate the suggestions from everyone. I did try all of them. I finally believe the problem is solved! I found this TSB and replaced the Supercharger gasket.

File In Section: 6E - Engine Fuel & Emission
Bulletin No.: 77-65-15
Date: May, 1997
Subject:
Idle Surge or Increased Idle
(Replace Supercharger Outlet Gasket)
Models:
1992-95 Buick Park Avenue
1995 Buick Riviera
1992-95 Oldsmobile Ninety Eight
1995 Oldsmobile LSS
1992-95 Pontiac Bonneville
with 3800 Supercharged Engine (VIN - RPO L67)
Condition
Some owners may comment about an engine idle surge, high idle (800 - 1000 rpm), or MIL (Malfunction Indicator Lamp) illuminated with DTC (Diagnostic Trouble Code) P0131, P0171 or 44 set, depending on model year.
Cause
Supercharger outlet gasket may be split near the front of the supercharger (pulley end) creating an air/vacuum leak.
Diagnostics
Install a scan tool device in the vehicle. Turn air conditioner off. Warm the engine up to operating temperature. With the engine at idle, brake pedal depressed, and gear selector placed in drive, monitor IAC (Idle Air Control) counts along with Long/Short term Fuel Trim numbers. If IAC counts are less than 15 and Long/Short term fuel trim numbers are greater than 140, an air leak should be suspected. Check for and repair any air leaks around vacuum hoses, connections, and vacuum controlled devices. If the condition is still present, check for an air leak near the front of the supercharger (pulley end). If an air leak is detected in this area, remove the supercharger assembly and replace the supercharger outlet gasket.
Correction
Replace the supercharger outlet gasket with an updated gasket that has been redesigned to provide better long term sealing. Thoroughly remove the old gasket material from the intake manifold and supercharger assembly. Install the service supercharger outlet gasket dry; use no sealers.

Just curious in case you don't have it fixed , what brand is your O2 sensor? I've heard of Bosch O2s going out within 5k miles and doing some funky things.

It's a AC Delco o2 sensor. I put on about 50 high traffic stop and go miles today, so far so good. Thanks