Another common mistake is to not assign actual values and just assume that the part is working properly. This is very common with fuel pressure and voltage. A test light is a good tool when used properly, but it doesn't replace a voltmeter. Similarly, just because the carburetor or EFI system has gasoline going to it doesn't mean the pressure is correct. There is a reason why Pontiac provides operating specifications in the shop manual. Nowhere does it replace numbers with an assumption.
The craft of diagnosing is a skill that will grow over time. Use your and others' experiences as learning tools. Show interest when someone else finds a problem with their Pontiac, and ask them about the symptoms and what eventually was determined to be wrong. When you find the problem with your own car, don't just be satisfied that it's finally fixed. Identify where you went wrong in your procedure, and think about and study the component or circuit to gain a better understanding for the next time. The best diagnostic people use lessons learned from something else to help fix the problem at hand.
To this cause, HPP has prepared this primer to help you get into the right area when diagnosing a problem with your Pontiac. Some of the information you may have seen before in HPP when discussing a particular component or theory, but not as a diagnostic lesson as presented here. Our goal is to make you into the Dr. House of the Pontiac world. And if you don't know who he is, check your local TV listings and watch an episode. The only thing we don't want you to emulate is his arrogant attitude!
EGR
Symptoms: Rough Idle, Stalling, Hesitation, Bog, Ping
The exhaust-gas recirculation valve is an emissions-control device that reintroduces spent gas into the combustion chamber to limit the amount of combustible mixture, and thus, the flame temperature. Elevated combustion temperature creates an emission called oxides of nitrogen (NOx). An EGR valve is usually vacuum controlled, though later OBD-II versions may use an electric solenoid instead of differential pressure.
A common problem with the system is carbon buildup. If this occurs under the pintle of the valve, it will hang open and the engine will idle roughly, and possibly stall or bog when the throttle is opened slightly. If the transfer passage is carboned closed or partially closed, the engine may ping at light throttle openings no matter how much you retard the timing.
To identify a carbon-laden passage, while wearing insulated gloves, reach under the valve and push up on the diaphragm while the engine is running. It should run very rough and possibly stall. If it has little impact on the idle quality, the passage is carbon-clogged and will need to be cleaned out.
To check for a poor sealing pintle or carbon under it, the valve will need to be removed and inspected. Pour a liquid, such as WD-40, on the pintle to see if it leaks. It should not.
Mass Air Flow Sensor
Symptoms: Stalling, Check Engine Light, Poor Performance
Early MAF sensors were very susceptible to premature failure, especially the Bosch-produced unit used on TPI engines. It employed a burn-off cycle that would glow the sensing wire at 1,000 degrees F when the key was turned to Off and the ECM was in closed loop in order to remove contaminants. If the burn-off relay sticks closed, the sensor will fail because the wire will break. If the relay isn't replaced, then the new sensor will fail because the burn-off is on all the time. This type of failure illuminates the CE/SES light.
A more elusive problem is a sensor that is beginning to fail which has a loose solder joint in it. This will cause the car to buck and possibly stall, but it will usually idle fine.