andyfreelandy

andyfreelandy

Well-Known Member
One of the fleet failed on the above. Fast idle all good co 0.28, hc 11, lambda 0.993. But idle gave co 1.45 %vol against limit of 0.5. Running ok and plugs clean, filter clean etc. Is there any idle adjustment? Any clues from the 1.8 gurus?! Many thanks
 
Good question! Data not on print out. I'm thinking cat is ok as it is alright at higher revs. Just hooked it up to my old gunsons CO meter. Bit hit and miss but certainly it is above 1%. I can go back and get hc and lambda at idle if it helps diagnose. Is there anything that would throw the CO out at idle and not at higher revs? Any adjustments? Figure not as it is closed loop. Thanks
 
Engine was hot although car not been used for a while before then. Gave it a bit of an italian tune up on the way! Just found a post on tps reset, done that and it ticks over at about 300rpm higher. Will redo CO test tomorrow on my machine. Is the O2 sensor you mean the one before the cat? I could alter the idle mixture on my MGF with my T300 programmer but option doesn't exist on this car. I can volt test the O2 I think!!
 
If the idle is too low, then that can affect the idle mixture, as it can drop outside the control window. The ECU will run open loop as it think there's a problem, although it would normally light the MIL.
 
Had a hunch this morning!! Must get some medication!! Removed the IACV and piston was stuck solid...closed. Found a spare and piston can be moved up and down carefully with a rod inserted to open the valve. Swapped IACV and on face of it prob is sorted. Gunson gauge says 0 CO!! So hope that is it. I suppose no fault code as solenoid was intact and engine was just struggling to deal with rich mixture. Tickover now steady. Exhaust smells better and hot start is on the button. Anyone else had this? Can piston be freed? Soaking perhaps?
 
Can anyone confirm whether the IACV piston should move without power to valve please? Want to confirm diagnosis! Another way is to false feed suspect valve. One manual diagram shows a motor another shows a solenoid!!
 
From memory, the IACV is a piston valve which is driven by a stepper motor shaft with an ACME thread. So in theory the piston valve can't move, except when the stepper rotates.
 
Thanks. Changing it seems to have solved problem, but will energise suspect one. I think I read in another of your responses that the ecu cycles the valve at ignition on so will try that to see if it is really stuck!
 
andyfreelandy said:
Thanks. Changing it seems to have solved problem, but will energise suspect one. I think I read in another of your responses that the ecu cycles the valve at ignition on so will try that to see if it is really stuck!
Click to expand...

Difficult to energise it unless you has a stepper driver. But yes, the ECU cycles the stepper at ignition on, and ignition off too IIRC. So you could plug in the IACV and see if I moves when the ignition is cycled.
 
Further testing reveals....the original sings a high pitch whistle and didn't move with ign cycling until cleaned. The spare sings but also clicks for about 10 secs whilst it finds the position it is happy with! Incidentally ran engine with IACV disconnected and it runs ok but very rich. Am hoping valve was stuck causing the rich idle and the clicking when ignition turned on is normal??
 
It will make some noise when it's moving, as the motor indexes round it's range of movement.
 
Andy, I suspect that this is a sign that the car's lambda is on its way out. You often see this on sensors that are about to fail - they run better when properly hot, but when cold (as may happen at a natural idle speed), it will go out of range, leading to over-rich fuelling.

If you can get your car on a diagnostics kit that can show live telemetry, you'll see the tell-tail lambda signal...
 
Get a ELM327 with torque pro app ,for live data an some code is good ,you can graphics lambda on line chart .
screenshot (1).jpg
 
Thanks both. Little bit new to me. My MGB don't have one!! Is the trace shown a good O2? Does torque pro produce the waveform or just the data. Need to check it before removal as it looks like a pig to remove!!
 
Lambdas are a complete pig to remove - usually stuck in there very solidly. Often best to just cut off the cable, then you can get a decent 6-point socket on it.

The Lambda sensor signal above looks normal. As they age, the amplitude reduces, and the mean signal tends to be higher.
 
Getting probs with torque pro. Get most data but o2 test is showing as not a function. Did you .get it to work on a 1.8 K series please? Mine is a 2002. Thanks
 
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