Hi, I've sent my toyota prado 1998 (RZJ 95, engine 3RZ, petrol) to diagnostic and it shows 3 error codes: 1. code 31: intake air pressure sensor vacuum sensor signal abnormal 2. code 14: IGT or IGF circuit of ignition system fault 3. code 24: intake air temperature sensor signal abnormal (open or short for more than 0.5 second) The only problem that I have with is car is that the RPM are not stable, when I start the engine, the RPM stays at 800 RPM than downs to 600 and go up to 900RPM.

"To have so many different codes at the same time indicates that the first place to start looking is the wiring harness itself. Locate the MAP (manifold air pressure sensor - code 31) and IAT (inlet air temperature sensor - code 24) connections. Disconnect and reconnect each sensor a few times and check that the connecting socket and pins are clean and free of corrosion - the codes indicate intermittent breaks. Check all fuses are clean and well mounted. Examine wiring harness for chafing, abrasion and signs of wear. Any intervening connections between the wiring harness and electronic control unit (ECU) need to be checked over and should be free of oily grime."

Thank you. About 2 months ago, my car stopped working (the check engine light turned on) and when I tried to shift the automatic transmission from Parkink to Drive, the engine stopped working. My mechanic changed the Air Flow Meter (that part near the air filter) and everything was fine, the only problem is that with the RPM, when I start on the engine, the RPM doesn't stay stable on 800 RPM, and the engine is making a noise like there's some air leaking from the system. I took my car to electronic diagnostic and it showed that 3 code errors, they said I must replace the vacuum sensor. I don't know if that is really necessary. "To have so many different codes at the same time indicates that the first place to start looking is the wiring harness itself. Locate the MAP (manifold air pressure sensor - code 31) and IAT (inlet air temperature sensor - code 24) connections. Disconnect and reconnect each sensor a few times and check that the connecting socket and pins are clean and free of corrosion - the codes indicate intermittent breaks. Check all fuses are clean and well mounted. Examine wiring harness for chafing, abrasion and signs of wear. Any intervening connections between the wiring harness and electronic control unit (ECU) need to be checked over and should be free of oily grime." Thank you. About 2 months ago, my car stopped working (the check engine light turned on) and when I tried to shift the automatic transmission from Parkink to Drive, the engine stopped working. My mechanic changed the Air Flow Meter (that part near the air filter) and everything was fine, the only problem is that with the RPM, when I start on the engine, the RPM doesn't stay stable on 800 RPM, and the engine is making a noise like there's some air leaking from the system. I took my car to electronic diagnostic and it showed that 3 code errors, they said I must replace the vacuum sensor. I don't know if that is really necessary.

The air mass meter is basically two components in one: a mass air flow (MAF) meter and the inlet air temperature sensor (IAT). The MAF is heated film of metal which is cooled by the incoming air. The ability to cool the film is a function of the amount of air entering and the temperature of that air, hence the IAT along side the MAF.
If you suspect a vacuum leak simply inspect all the tubes that connect with the inlet manifold plenum for cracks and poor connections. Tubes to look for are:
positive crankcase ventilation valve,
brake servo assist tube,
transmission gear sustain tube,
fuel pressure relief valve,
manifold absolute pressure sensor,
evaporative vapour control tube.
If you suspect a particular tube a quick spray with WD40 will cause a temporary jump in revs if the leak is real. Also check the fuel injector seals and the junction between the inlet manifold and the cylinder head.
The 'vacuum sensor' is the Manifold absolute pressure sensor. This device simply measures the difference between the normal external air pressure and the partial vacuum that the engine creates within the inlet manifold.
How does it work? When the engine is at idle the throttle plate is fully closed and the vacuum within the inlet manifold is at its greatest, 20 inches (~500mm) mercury.
Symptoms of a faulty MAP:
• Poor starting/erratic idling/engine stall - with the MAP not sending the correct inlet air pressure signals to the ECU, incorrect fuel injection volumes then result. The imbalance in the fuel/air ratio often leads to rough engine performance and poor starting and stall. The engine might be kept running at start up by pumping the accelerator pedal
• Sluggish performance/power ceiling - the engine may seem to perform normally in the lower rev range but will severely run out of power above about 3000 rpm
• Poor fuel economy. The ECU tends to supply an over rich fuel mix to the engine in the absence of signal from the MAP resulting in very poor fuel economy. The reason for this is that if the MAP has no signal this means no vacuum = fully open throttle = engine is under load. To match this ‘open throttle’ signal the ECU increases the injection cycle to supply more fuel.

How to Check? The device has three electrical pins, one for 12 volts (or 5 volts) reference, one for ground and the third (the middle one generally) is the ‘signal’ output. Put a voltmeter positive connector on the ‘signal’ pin of the connected socket (back probe by inserting a bit of wire). Apply suction to the vacuum input, even sucking on it with your mouth, should result in a measurable voltage output. At normal air pressure (open throttle) the voltage seen should be 0 volts. As vacuum is applied the voltage output should change to about 5 volts (throttle closed at idle). If no voltage transition is seen the MAP is faulty. The air mass meter is basically two components in one: a mass air flow (MAF) meter and the inlet air temperature sensor (IAT). The MAF is heated film of metal which is cooled by the incoming air. The ability to cool the film is a function of the amount of air entering and the temperature of that air, hence the IAT along side the MAF. If you suspect a vacuum leak simply inspect all the tubes that connect with the inlet manifold plenum for cracks and poor connections. Tubes to look for are: positive crankcase ventilation valve, brake servo assist tube, transmission gear sustain tube, fuel pressure relief valve, manifold absolute pressure sensor, evaporative vapour control tube. If you suspect a particular tube a quick spray with WD40 will cause a temporary jump in revs if the leak is real. Also check the fuel injector seals and the junction between the inlet manifold and the cylinder head. The 'vacuum sensor' is the Manifold absolute pressure sensor. This device simply measures the difference between the normal external air pressure and the partial vacuum that the engine creates within the inlet manifold. How does it work? When the engine is at idle the throttle plate is fully closed and the vacuum within the inlet manifold is at its greatest, 20 inches (~500mm) mercury. Symptoms of a faulty MAP: • Poor starting/erratic idling/engine stall - with the MAP not sending the correct inlet air pressure signals to the ECU, incorrect fuel injection volumes then result. The imbalance in the fuel/air ratio often leads to rough engine performance and poor starting and stall. The engine might be kept running at start up by pumping the accelerator pedal • Sluggish performance/power ceiling - the engine may seem to perform normally in the lower rev range but will severely run out of power above about 3000 rpm • Poor fuel economy. The ECU tends to supply an over rich fuel mix to the engine in the absence of signal from the MAP resulting in very poor fuel economy. The reason for this is that if the MAP has no signal this means no vacuum = fully open throttle = engine is under load. To match this ‘open throttle’ signal the ECU increases the injection cycle to supply more fuel. How to Check? The device has three electrical pins, one for 12 volts (or 5 volts) reference, one for ground and the third (the middle one generally) is the ‘signal’ output. Put a voltmeter positive connector on the ‘signal’ pin of the connected socket (back probe by inserting a bit of wire). Apply suction to the vacuum input, even sucking on it with your mouth, should result in a measurable voltage output. At normal air pressure (open throttle) the voltage seen should be 0 volts. As vacuum is applied the voltage output should change to about 5 volts (throttle closed at idle). If no voltage transition is seen the MAP is faulty.

Thank you. I always use injector cleaner fluid when I put fuel in the car. What do you think is causing the codes errors (14,24,31)? Thank you. I always use injector cleaner fluid when I put fuel in the car. What do you think is causing the codes errors (14,24,31)?

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