This effectively blocks the core when the water pump is at low output (idle). The most common culprit is carbon buildup on the throttle body, exhaust gas recirculation (EGR) valve and idle air control (IAC) valve. Dirt is the greatest cause of premature air valve failure. So, If you have an older vehicle, you may have a dirty idle air control valve. 2.) If your car's idle is rough, possibly rising and falling, or struggling to maintain a steady rate of rotation, you may have a problem that needs fixing. Since a smooth idle depends on just the right mixture of fuel and air, there can be many possible places where that combination is getting unbalanced. It may almost stall, or it may run at varying RPMs without your putting your foot on the gas, or it may do both. No leaks detected. I changed the air governor to no avail. Trapped air can be in the core, but it blows out with increased water pump pressure. It is possible that the drive catches intermittently, but that is rare. When you start the engine, it won't run at a steady rate. It has an air dryer but that is not constantly unloading Any advice on what the problem could be ? The computer doesn’t know the carbon buildup is there..all it knows is that the engine isn’t running right based on it’s calculated opening. Also, Some idle air bypass or idle air control valves can … It would build up to 60 PSI, and i could rev it beyond that, but it would always drop back down to 60. Complete air dryer service within the last 6 months. Searched forums with no luck. The idle air control valve — also known as the "idle speed control valve" — regulates the idle speed of your engine. M925A2 not building air at idle. AIR BRAKE SYSTEM TROUBLESHOOTING 1.) Check to see if your idle control valve is functioning properly before attempting to replace it. This is not a normal operating condition. The hypothesis that air the core is the issue is at odds with itself. Diesel Air Brake Compressor Drive Failure:If the compressor drive failed, in most cases the compressor won't put out any air at all. This is controlled by the engine's computer. Before replacing any valve with a new or remanufactured valve, be sure to blow the air lines out either using the vehicle’s own air supply or shop air. It does not make sense that the trapped air re-establishes itself every time you reach a stop sign. You may have noticed that your car, truck, or SUV has developed a rough idle. So, I had the compressor rebuilt, put it back in yesterday without the regulator and now it won't build any pressure at all. If pipe dope is used on fittings, use it sparingly. Sometimes parts go bad, which results in your car idling strangely or stalling. This simple procedure can often bring an EGR valve back from the dead and restore a smooth idle. Could it be the PPV valve? In this case, you are required to disassemble the sensors out of the throttle body. 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