Replace air control valve if faulty

Q1 a.) I have a 2007 Honda City VTEC.

During startup of the vehicle, it is fine while idling but when engaged in D gear, it will suddenly choke and the rpm will plunge low and to 0, and bounce back up above 1,000rpm mark.

The choking would sometimes happen more than once until I disengage the gear in Neutral mode. I have cleaned the throttle body and reset the ECU as advised by my mechanic.

However that didn't help and it occurs only during startup of the vehicle. The mechanic mentioned it might be a faulty IACV sensor but it's expensive. I want to evaluate other options first. What does the IACV do?

b.) Due to the occurrence only during startup and while applying brakes, could it be a vacuum leak between master cylinder and booster? If that is the case, should I repair, replace or service?

c.) I have also noticed there is an oil leak around the oil filter area.

Thomas
Shah Alam

In answer to part a, the Intake Air Control Valve (IACV) is NOT a sensor, it’s an actuator. It is attached to the throttle body assembly with wires connected to the ECU and cannot be repaired.

If this component is found to be faulty,  it must be replaced.

Please refer to the specific service manual for more details.

The valve controls the intake air volume not only during start-up but also when there's additional pressure from other components like when you apply the brakes, or during additional engine load operation when the alternator and compressor magnetic clutch are on, etc.

To check it, first, see if there is any DTC (diagnostic trouble code in the IACV circuit) using a scan tool.

If you do not have a scan tool, follow the troubleshooting procedures in the manual. if you have neither, use test parts. If the problem disappears then it is a faulty IACV.

If the IACV is faulty and not replaced as soon as possible it can damage the ECU.

b.) If there is a vacuum leak on one of the hoses connected to the intake manifold like at the booster hose, rough idling will always occur.  You will also either find difficulty when pressing brake pedal or your braking is not that efficient. Since there’s no problem in braking, your problem lies elsewhere.

c.) For this oil leak, check the gasket and oil seals of the parts connected to engine block like the VTEC spool valve, cylinder plug, etc. If they are OK, the oil filter may have been over-tightened that the  oil filter o-ring was damaged (in this case, change the whole oil filter. Hand-tighten for appropriate torque.


Q2: The clutch on my Subaru Impreza WRX is slipping when it is driven quite hard but not when taking it steady. The car gives off a minor judder when pulling off. The clutch may need to be replaced. I need a second opinion.

Izam
Pontian

You did not say how old the car was.

Replace the clutch component and pressure plate if the car shows these symptoms

> Assuming the clutch had never been replaced before, no noise occurs during shifting but on first gear juddering occurs when the clutch is released, hence needing higher rpm before the car runs smoothly on this gear;

> slipping on the other gears,

Get the technician's confirmation before replacing these items.


Q3: I have a hand-me-down Renault Clio 1.2. It had been sitting in the backyard for the past seven months. Recently, I started using it but there's a problem.

When accelerating through the gears the power drops off for a moment at about 2700-2800rpm. This occurs intermittently.

The engine speed drops by about 100rpm and I feel a loss of power and acceleration. Am I looking at replacing a faulty oxygen sensor?

Richard
Penang

The oxygen sensor does not affect the idling or the engine rpm. When it is faulty, a 'check engine' warning indicator will light up in the instrument panel, or it might display after you rev the engine to 3000 rpm for several seconds.

You will also get a DTC when you check using scan tool. When you switch off the ignition, then turn it back on, the 'check engine' indicator will go away but comes back again when you start and rev the engine to a higher rpm.

But if any of the above is not occurring, try to check first and replace the preventive maintenance items like the air cleaner, spark plugs, and fuel strainer. If it occurs while the A/C on, you need to have your a/c system checked and cleaned if necessary.

If all those preventive maintenance items are in working order, check the ignition coil.