QuestionQUESTION: I have a 1996 lancer gli and it's (red) check engine lights goes on and off even when driving, the idle is not stable when i open the aircon, goes up and eventually the engine goes off. but when the aircon is not being used, the idle is stable but the engine light still opens and closes. not like a christmas light but only when there is a change in idling. this incident have been going on for such a long time now, i am the one who is adjusting to the situation.i only open the aircon when i'm running, and puts it off when i'm in a full stop. i'm from Manila, Philippines,can you help me with this?
ANSWER: You have a vacuum leak, probably. The HVAC system is operated by vacuum. There are a bunch of little vacuum motors that open and close the doors under the dash, the valve for the heater water, etc. To ensure that they always have enough vacuum to operate correctly there are several vacuum reservoirs located on or near the firewall. They look like little round black things about 12 cm in diameter. Most likely one of these has failed and is leaking. But, it could be one of the lines that supplies the vacuum. You'll need a squirt bottle full of washer solvent (the kind with alcohol in it). Follow each line and squirt the solvent anywhere that there is a joint or crack. This must be done with the engine running, you may have to crank up the idle screw to keep it running. When you find the leak, the engine will suck in the solvent and briefly run a little faster. Fix the leak and you're good to go.
If the car has OBDII controls (if it were in the U.S., they would be required, but I don't know about Manila) there may be a faulty idle control motor. This is a small motor that controls the idle by passing air around the throttle plate. It is controlled by the computer. If it is bad, it can act just like you are describing, except for the air conditioning business. That would be possible if the computer was using some other means to raise the idle to compensate for the load of the A/C compressor. First thing to do, if the car has OBDII, is to get a garage to check the computer for trouble codes. Even when the light's not on, the computer stores them. If they are in there they will tell you what's wrong.
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QUESTION: am not familiar with the hvac, but a mechanic also told me about the servo kit that controls the idle of the engine, i think all of these has to do with the stable idling of the engine regardless wether the A/C is on or off, if the A/C is on, the engine is having trouble coping up and eventually shuts off if the car is in a full stop, but if the car is running, no problem w/ the A/C and engine.
Answer Exactly. The idle system keeps the idle at a fixed value, opening and closing the bypass valve to compensate for the varying loads on the engine. The A/C compressor is the biggest load, that's all. If you are sitting still at idle and start to saw the steering wheel back and forth it will increase the load on the power steering pump and you will hear the engine speed changing as the idle motor tries to keep up. The computer can respond in milliseconds, but the engine itself takes a while to react. Idle speed motors can become gunked up inside. When this happens, the little motor that opens and closes the valve becomes over-loaded and burns out. Replacing the Idle Speed Motor is probably what you are going to have to do. They are not too expensive. Make sure that the passages leading to the idle motor, and the throttle body itself, are thoroughly cleaned when the job is done.
