Idle Air valve bypasses IAT sensor

[ellisd1984]

I've got a celica ST205 which has the standard IAT sensor after the TB in the inlet manifold.  The sensor is slow and heat soaks really bad and will pretty much just sit at 40 ded C so is pretty useless.

To  fix that I installed one of the link/Bosch open element sensor just before the TB which works much better apart from at Idle with the TB closed the air for the engine it fed from a separate pipe from essentially where the air filter is and bypasses the charge pipework & IAT sensor completly.  I've tried a couple of times to switch Charge Temp Correction on as it sounded like that was designed for exactly this problem but I couldn't get it to work at all so If someone else has had this issue how are you all getting around it?

Thanks David

[Adamw]

It would be pretty unusual for the throttle body to be completely closed with all air coming from the idle valve?  Charge temp approximation is not designed to cover for a sensor that is not exposed to the air entering the engine, it is designed to account for the heating of the air that happens after the sensor - it still needs to know the correct initial air temp.

[ellisd1984]

Presumabley then it would mean if my IACV duty cycle is at 40% at warm idle there's nothing stopping me from adjusting the throttle blade open more and reducing the duty cycle at idle? 

if I sit at idle with a heat socked engine the IAT sensors climbs really quickly but if I manually touch the throttle just a crack (less than 5%) the temps reduce significantly,  anything over 5% and there isn't an issue as enough air is passing by the sensor anyway.

I'm going to have another crack at charge temp correction as well but it hard to tell well I should be adding/reducing fuel to the main fuel map or changing the CTC bias.  When tuning the idle area and biasing 100% to ECT I still had to add 20% fuel (idle area was previously tuned) to that area on the main fuel table to get me to lambda 1.

[Adamw]

3 hours ago, ellisd1984 said:

Presumabley then it would mean if my IACV duty cycle is at 40% at warm idle there's nothing stopping me from adjusting the throttle blade open more and reducing the duty cycle at idle? 

Correct, crack the throttle open so the valve is down around 20% at normal warm idle and that should mean most of the air is going through the throttle.

 

3 hours ago, ellisd1984 said:

When tuning the idle area and biasing 100% to ECT I still had to add 20% fuel (idle area was previously tuned) to that area on the main fuel table to get me to lambda 1.

Yes you need to retune the fuel table any time you adjust the charge temp table.  The example values in the help file are generally a good starting point.

[ellisd1984]

21 hours ago, Adamw said:

Correct, crack the throttle open so the valve is down around 20% at normal warm idle and that should mean most of the air is going through the throttle.

Hi Adam, thanks for the reply. I've been getting my head around CTE and its starting to sink in be there was an issue with the throttle. On the UK 205 GT Fours (not sure if its just on the UK models) there's a little actuator which keeps the throttle open a crack until engine startup. Once there's vacuum acting on this actuator it was essentially letting the throttle blade shut completely. This was causing the only path for the air at idle to go through the IAC valve. I've adjusted the throttle blade stop and adjusted the IAC duty cycle acordingly and it's working much better now. It's also addressed a dead spot in my TPS as the throttle plate was closing an extra 6% after the TPS was calibrated and the engine was running.