2003 oldsmobile silhouette idles rough, starts to buck at around 2000 RPM wondering if my PCM is bad?

It's called IAC - idle air control valve > Did the RPM'S stay at 2000 or drop back down ? The PCM engine computer controls IAC valve according to engine load . Put it in gear , turn on electrical loads , headlamps , A/C etc... an the RPM raise's up so engine will not stall . More then likely the throttle plate needs to be cleaned , they get gummed up an stick at higher idle . Quick Tip Throttle Cleaning EricTheCarGuy If the IAC valve were gummed up the idle would be low or erratic . On some engines a vacuum leak will cause high idle . Videos on youtube checking for vacuum leaks .

Do you have a scan tool that you can see sensor data ? What are fuel trims showing ? Is the computer add fuel because of a lean condition ? Are the O2 sensors switching , do you know what that is ? Can a scan tool communicate with the pcm ? If so probably not a bad PCM .What are the IAC valve counts ? Can the PCM control the IAC valve ? Suggest you take it to a qualified repair shop that know's how to diagnose , an not just replace parts .

First eliminate all vacuum or air leaks in the system. You may have a bad IAC ( idle air control) but try cleaning the throttle body first. Remove the intake snorkel, have someone hold the throttle wide open for you and scrub the back side of the throttle plate and surrounding bore with an old tooth brush and some carb cleaner. Be sure to spray some into the small holes next to the throttle plate. That should help stabilize the idle. If it still has a problem, replace the IAC.

remove neg. cable from battery so the ECM will reset this may work. make sure the IAC is air tight. if this doen't fix your problem have someone check the IAC valve if it's bad the part runs $300.00 pluse

Why wasn't the Throttle Position Sensor replaced? The first suspect should probably have been the IAC (but you would have gotten a code), the next logical step would have been checking for something mechanical like the throttle body being gummed up and needing cleaning, but I would replace the TPS before I'd EVER think the PCM would need replacing...I'd hate to see that bill. I have a 2001 Aurora with a 4.0 and I have replaced the IAC (got one at a salvage yard, out of a Caddy, same one)-it did fix mine, but the next culprit would have been the TPS in any case, PCM's rarely go bad.

you need to clean your idle air control valve ( or replace it) Spray carb cleaner does a nice job of cleaning it.

This tutorial is from autozone.com

OPERATION

The Idle Air Control (IAC) is a bi-directional motor driven by two coils. The purpose of the IAC valve is to control engine idle speed, while preventing stalls due to changes in the engine load. The IAC valve, mounted in the throttle body, controls bypass air around the throttle plate. The PCM controls engine idle speed by adjusting the position of the IAC motor pintle. The PCM pulses current to the IAC coils in small steps (counts) to extend the pintle into a passage in the throttle body to decrease air flow. The PCM reverses the current pulses to retract the pintle, increasing air flow. This method allows highly accurate control of idle speed and quick response to changes in engine load. If RPM is too low, the PCM will retract the IAC pintle, resulting in more air being bypassed around the throttle plate to increase RPM. If the RPM is too high, the PCM will extend the IAC pintle, allowing less air to be bypassed around the throttle plate, decreasing RPM.

Fig. Typical Idle Air Control (IAC) valve components
During idle, the proper position of the of the IAC pintle is calculated by the PCM based on the battery voltage, coolant temperature, engine load and engine RPM. If the RPM drops below a specified value, and the throttle plate is closed (TP sensor voltage is between 0.20-0.74), the PCM senses a near stall condition. The PCM will then calculate a new IAC pintle position to prevent stalls.
If the IAC valve is disconnected and reconnected with the engine running, the idle RPM will be wrong. In this case, the IAC has to be reset. The IAC resets when the ignition switch is cycled ON and then OFF . When servicing the IAC, it should be disconnected or connected with the ignition switch OFF in order to keep from having to reset the IAC valve.
The position of the IAC pintle affects engine start up and the idle characteristics of the vehicle. If the IAC pintle is fully open, too much air will be allowed into the manifold. This results in high idle speed, along with possible hard starting and a lean air/fuel ratio. A Diagnostic Trouble Code (DTC) may set. If the IAC pintle is stuck closed, too little air will be allowed in the manifold. This results in a low idle speed, along with hard starting and a rich air/fuel ratio. Again, a Diagnostic Trouble Code (DTC) may set. If the IAC pintle is stuck part way open, the idle may be high or low and will not respond to changes in engine load.

TESTING

As with most all engine control sensors used in your vehicle, a thorough and proper test can only be performed by a qualified technician using a scan tool to read the data stream from the PCM. There are a few items a non-professional should check before taking the vehicle to a qualified technician for diagnosis and repair.

Check for a poor connection at the PCM or IAC motor. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connection. Inspect for a damaged wiring harness, especially if heavy work has recently been performed (intake manifold removal, engine removal, etc.) where the throttle body has been disturbed. Inspect for a restricted air intake system. Check for a possible collapsed air intake duct, restricted air filter element or foreign objects blocking the air intake system. Inspect the throttle body. Check for objects blocking the IAC passage or throttle bore. Excessive deposits, especially on high-mileage engines, can build up in the IAC passage and on the IAC pintle. Excessive deposits can also build up on the throttle plate, so check for a sticking throttle plate. Check for vacuum leaks such as disconnected hoses, leaks at the EGR valve and EGR pipe to the intake manifold, leaks at the throttle body, faulty or incorrectly installed PCV valve, leaks at the intake manifold brake booster hose connection, etc.

REMOVAL & INSTALLATION

1. Disconnect the negative battery cable.
2. Detach the electrical connector from the IAC valve.
3. Remove the 2 attaching screws and remove the IAC valve from the engine. Remove the O-ring from the housing.

To install:

Fig. The Idle Air Control (IAC) valve is mounted on the throttle body-3.8L (VIN K) engine shown, others similar

NOTE Before installing a new IAC valve, measure the distance that the valve is extended. The measurement should be made from the motor housing to the end of the valve cone (pintle). The distance should be no greater than 1 1 / 8 inch (28mm). If the pintle is extended too far, adjustment is required, otherwise damage may occur when the IAC valve is installed. Adjust the IAC valve by compressing the pintle to achieve the correct length.

1. Use a new O-ring, install the IAC valve and tighten the retaining screws to 18 inch lbs. (2 Nm).
2. Attach the electrical connector.
3. Connect the negative battery cable.
4. The PCM will reset the IAC valve the next time the ignition switch is turned ON and then OFF .
5. Start the engine and allow to warm to operating temperature to check idle quality.

the iac probably has carbon built up around it this controls the idle speed try cleaning it first,if not it could be a bad iac or a vaccum leak that the iac takes some time to compensate for to control idle.

You want to check your charging system. Take a reading at the battery and see what you get. it should be 13.5-14 volts. Check the volts at the cables. with the battery hook up take a reading at the cables. if there is a big difference between the cables and the battery then you need to clean and tighten your cables. If the volts are less then I said before then you need to have your alternator checked.

007 Idle Speed Problems Scan Data for Idle

you can't adjust the idle it's all done by the pcm.you might have a IAC going bad or sticking(idle air control solenoid)