How to adjust throttle position sensor and minimum air flow at idling

Ted · November 19, 2017

Hi all,

I am confused with setting the throttle position in order to get the optimim idling (i.e. Idle control valve functions at specified rates and at the specified idling rpm).

My car manual says,

1) when 0.4 mm thickness is between throttle stop screw and throttle throttle lever, throttle IDL and E1 pins should show conductivity.

2) when 0.9mm thickness is between throttle stop screw and throttle position lever, IDL - E1 should start showing open circuit.

When I adjusted the throttle stop screw in order to obtain above, I idling rpm was 1500 rev/min. This is too much. So I adjusted the throttle stop lever to obtain idle rpm to about 800 rev/min.

My question is how I should obtain both correct rpm setring and throttle setting (above 1-2) ?

Anyone who had same experience or expert please...

Rumesh88 · November 20, 2017

Carina AT192 is n't it? Hope you tried your adjustment with a fully warmed up engine. I will popup a few questions that comes to me almost immediately. Does your cold start routine work as expected? Was your IACV cleaned recently? It could be due to wrong adjustment of IACV or the throttle flap is not fully closing. Did you check/test/cleaned the IACV according to the manual before trying to adjust the idle screw?

Edited November 20, 2017 by Rumesh88

Ted · November 21, 2017

Hi Rumesh,

Thanks for the reply. Infact I did not check the IACV yet. I will check it and give you feedback soon. Rather I wonder there are two parameters to adjust. One is this ajdusting screw and the other is throttle position sensor. Manual does not say anything on adjusting screw. Manual says if 0.4 mm short cct and 0.9mm open cct is not given in throttle position sensor, then adjust the throttle position sensor. What I did was adjusting the screw. For this setting screw set up to maximum throttle opening.

I searched in videos, there are some complex activities to do in order to tune these all. Need an IAC actuator as well. Any comments?

Will get back to you soon with your answers...

Rumesh88 · November 21, 2017

I assumed that you followed what the manual says. Instead what you did was the reverse (in fact you were trying to adjust the screw to get the correct positioning of TPS). You need not worry about IACV for now, but first get the TPS adjusted for the above setting. Begin with a fully closed throttle and keep a gap of 0.4mm. With engine off, check for IDL-E1 short circuit. Then move the throttle for a gap of 0.9mm and check for open circuit. If the two events does not happen then rotate and adjust TPS position. Also check if the resistance reading of the TPS slider contact moves smoothly without blank spots particularly close to idle position.

Ted · November 21, 2017

On 11/21/2017 at 2:28 AM, Rumesh88 said:

I assumed that you followed what the manual says. Instead what you did was the reverse (in fact you were trying to adjust the screw to get the correct positioning of TPS). You need not worry about IACV for now, but first get the TPS adjusted for the above setting. Begin with a fully closed throttle and keep a gap of 0.4mm. With engine off, check for IDL-E1 short circuit. Then move the throttle for a gap of 0.9mm and check for open circuit. If the two events does not happen then rotate and adjust TPS position. Also check if the resistance reading of the TPS slider contact moves smoothly without blank spots particularly close to idle position.

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At what adusting screw set up i should do this? Since I am not the firsr who adjusted this screw... i rem when i went for engine tune up several months back the mechanic adjusted this screw to set the idling rpm.

The Stig · November 21, 2017

You should not screw around with the throttle position, pun intended.

The throttle position is set from the factory and shouldn't really be messed around with unless you have a way to read the voltages.

You should adjust idle from the idle adjust screw, im not sure where exactly yours is located but it should be in parallel to the throttle plate.

Also your throttle position is reset every time you reset your ecu (removing the battery) so there is no point in adjusting this. There is a minimum operating voltage for the tps (usually 0.20v) if you go below this it will give a check engine light.

Ted · November 21, 2017

On 11/21/2017 at 4:49 AM, The Stig said:

You should not screw around with the throttle position, pun intended.

The throttle position is set from the factory and shouldn't really be messed around with unless you have a way to read the voltages.

You should adjust idle from the idle adjust screw, im not sure where exactly yours is located but it should be in parallel to the throttle plate.

Also your throttle position is reset every time you reset your ecu (removing the battery) so there is no point in adjusting this. There is a minimum operating voltage for the tps (usually 0.20v) if you go below this it will give a check engine light.

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Problem is just adjusting screw will only adjust idle rpm. Not the 0.4mm - short cct/0.9mm open cct reqiirement to ecu.

Rumesh88 · November 21, 2017

On 11/21/2017 at 3:07 AM, Ted said:

At what adusting screw set up i should do this? Since I am not the firsr who adjusted this screw... i rem when i went for engine tune up several months back the mechanic adjusted this screw to set the idling rpm.

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That's the wrong way to adjust idle RPM in this engine. For the TPS adjustment (if required) that can be done by loosening its two mounting screws and rotating it. TPS can be rotated within a small angle. You need not bother about TPS voltage in this case because this TPS has its idle position contact unlike the three terminal TPS in some other engine models. BTW does your engine stall when you fully retract idle screw?

Davy · November 21, 2017

Agree with Rumesh.

One of the biggest mistakes our makabases make is mess with the idle adjustment screw. In an engine with an automatic idle adjustment mechanism (i.e. one with an idle air control valve), adjusting the idle adjustment screw is asking for trouble. I once had idling issues after a tune up done the previous day and couldn't for the life of me figure out what was wrong until I removed the rubber dust cap covering the idle adjustment screw to find out that they've adjusted it (factory paint mark on the screw was not in position). Once I aligned the paint mark, it was idling perfectly again. On most workshop manuals, there is a warning against changing the position of the screw.

So why on earth have a screw in the first place? it's because most of these components (throttle body in this case) are used interchangeably between different engines and cars. Depending on which car the throttle body is on and which ECU model is controlling it, the idle screw is set from the factory.

Also, adjusting the TPS is also not the way to adjust idle RPM. All that does is, create an offset between the actual throttle position and the set angle. This is exactly like gently pressing the throttle with your foot to keep the RPMs elevated to prevent the engine from dying.

If I'm not mistaken, the AT-192 has an adjustable, camshaft driven distributor. If at some point the distributor was taken out or adjusted, it might be that ignition timing is now retarded, causing the engine to die. The distributor must be rotated to the correct angle so that the idle RPM is proper. This is best done while the car is plugged into a scanner while monitoring that all values fall within range for your engine.

Ted · November 22, 2017

On 11/21/2017 at 3:31 PM, Rumesh88 said:

That's the wrong way to adjust idle RPM in this engine. For the TPS adjustment (if required) that can be done by loosening its two mounting screws and rotating it. TPS can be rotated within a small angle. You need not bother about TPS voltage in this case because this TPS has its idle position contact unlike the three terminal TPS in some other engine models. BTW does your engine stall when you fully retract idle screw?

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will check all and let you know..

Ted · November 24, 2017

On 11/21/2017 at 11:29 PM, Davy said:

Agree with Rumesh.

One of the biggest mistakes our makabases make is mess with the idle adjustment screw. In an engine with an automatic idle adjustment mechanism (i.e. one with an idle air control valve), adjusting the idle adjustment screw is asking for trouble. I once had idling issues after a tune up done the previous day and couldn't for the life of me figure out what was wrong until I removed the rubber dust cap covering the idle adjustment screw to find out that they've adjusted it (factory paint mark on the screw was not in position). Once I aligned the paint mark, it was idling perfectly again. On most workshop manuals, there is a warning against changing the position of the screw.

So why on earth have a screw in the first place? it's because most of these components (throttle body in this case) are used interchangeably between different engines and cars. Depending on which car the throttle body is on and which ECU model is controlling it, the idle screw is set from the factory.

Also, adjusting the TPS is also not the way to adjust idle RPM. All that does is, create an offset between the actual throttle position and the set angle. This is exactly like gently pressing the throttle with your foot to keep the RPMs elevated to prevent the engine from dying.

If I'm not mistaken, the AT-192 has an adjustable, camshaft driven distributor. If at some point the distributor was taken out or adjusted, it might be that ignition timing is now retarded, causing the engine to die. The distributor must be rotated to the correct angle so that the idle RPM is proper. This is best done while the car is plugged into a scanner while monitoring that all values fall within range for your engine.

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Hi Davy,

Yes indeed it is. This has no G signal. Only NE+ & NE- signals from which ecu calculate RPM. Engine is tuned well (Water is coming from the silenser). Does it mean that timing is properly adjusted? Or is there anything else to be checked specially for the idle rpm setup?

Ted · December 14, 2017

My problem was how to set the adjustment screw to the factory or correcr position. I found in an article that this screw is there to keep a lil air through otherwise the throttle plate will be sticked due to air pressure. And also minor adjustments of it will not change idle rpm since ECM will nullify it by learning. I too expereinced this stick since recently I adjusted this screw such that throttle flap is more closed. Now I am going to do first is set this screw up not to stick the throttle plate. Then adjust the TPS. Any comments?