AIR/FUEL SENSOR FAULTY???

[JO3]

hey ppl...
i've written on this forum before regarding my problem with the car's revving...

well..u guessed it...it's back again.....
and this time..the car's idle goes up and down...
and when it does stay constant..it's at the 1500 mark...
the car even jerked like mad...with the engine revving up and down while i was driving..causing it to stall a few times...

so this is what happened...
my mechanic told me that it was the air/fuel ratio sensor....
and instead of chaging the whole thing...which will cost a fair bit...
he cleaned it up to see if it would fix the problem......
but it didnt work....

so my question is....
has anyone experience this problem before and if u have...
what was your solution to it?..
am i just wasting my time trying to fix the sensor when it is a must to get it changed?...
also...if u did get that part changed..how much did it costs?....
and lastly...could it be another problem besides the sensor...

this is what i've done so far:
1) cleaned the whol air flow system...
2) cleaned the throttle body...
3) cleaned the injectors...
4) cleaned the air/fuel ratio sensor (it's just behind the inlet manifold)

thanks ppl for the help...
joe

[bennjamin]

PCV valve....ECU fault....Have u even check ur ECU in diagnostci mode for any bad codes it may show ? COULD be a hint of whats wrong....

[wynode]

What's an Air/fuel ratio sensor?

If its also happening under WOT i'd say its not the O2 sensor as that only affects close loop operation. I'd be looking at a faulty MAP sensor, and like ben said......check the ECU for diagnostic codes.

[Breeze]

Disconnect the Idle Air control valve (IAC) when the car is hot and then restart. Depending on your engine, it ofen sits on the back of the intake manifold. When you disconnect the IAC the car runs at the exact idle speed it is set at (750rpm). Sometimes a dirty IAC can cause it (the IAC) to stuff up but if it has been cleaned it may be knackered.

This test indicates that either your IAC /ECU (or one of the sensors sending info to the ECU) is on the blink. Or you have a vacuum leak.


Disconnect IAC and car continues to run at a high idle speed then it could be a vacuum leak caused by faulty gaskets OR the fast idle thermo valve has failed (this one usually is attached to the throttle body and has no electrical plug, just two coolant lines).

If the car returns to normal idle speed then your IAC or ECU or sensors such as the Map sensor my be on the blink. Usually very rare for an ECU to partially fail like that so first finger point would be the IAC.

If you get normal idle after disconnecting IAC you could try and turn the car off remove the 7.5A backup fuse for at least 10 seconds, reconnect the IAC plug and restart (this is the process for resetting idle speed.

[JO3]

well...we have tried disconnecting the IAC(if this is the black plastic piece behind the inlet manifold) and it works fine for like 2-3 minutes then the problem starts again...

then we cleaned the IAC and the problem was still not solved....

so now my car is in the workshop to see what other thing is wrong b4 getting the IAC changed...

anyone else who knows whats wrong?..

thanks..

[Breeze]

Sorry-if you disconnect the IAC the idel should be between 370 and about 470rpm (not the speed you want it to idle atas you may have understood from my other post). When you reconnect IAC this should be back around the 700-800 mark. If your base idle speed is too high the IAC will not be able to control idle and you will get surging. This can be caused by vacuum leak (ie throttle body gasket or idle speed screw too far out).

Remember base idle speed with IAC unplugged should seem ridiculously low, almost stalling.

[JO3]

well...now that we've took the whole IAC out and gave it a good clean..
the problem still occurs...
and breeze..as far i remember when i plugged out the IAC plug...the car stalled totally...

when i checked the car just now....
this was what happened...
stepped on the accelerator and when i let go...the rev drops to almost zero and then up again...but car did not stall...
and when i lay my foot's on the accelerator constantly...
the engine revs up and down by itself...

ben and wynode...nope i have not check the ecu in a diagnostic mode as my mechanic does not have that in his shop...

but my mechanic said that it's very likely that the problem is coming from the IAC..i just wanna be sure that if the IAC is spoil...such problem will occur...
cos the last thing i want is to spend money changing the IAC just to find out that the problem is somewhere else...

[Breeze]

If that is done (revs up and down by itself) when your IAC is disconnected and your foot is just on the accellerator then there is a good chance it is a vacuum leak somewhere else. If the revs dropped and then came up again to say 600rpm then adjust the idle speed screw on the throttle body so the idle is really really slow, just above stalling and constant (screw it right in and then about 1/2 a turn out is usual set position). Then do the ECU reset and plug the IAC back in before starting.

An IAC is about $400 retail from Honda for a B16A so I hope it is not that. If you undo the bolts holding on the IAC (two bolts). Pull it away from the manifold so you can see the plunger. Then turn the ignition to the on position and plug the IAC in while watching what is happening. The plunger should move as soon as you plug it in and it will let out a low continuous groan/hum sound. If it does this it may still be okay.