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Throttle Not Fully Returning


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#1 kangaroomadman

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Posted 24 October 2018 - 06:46 PM

I seem to have an issue with a sticky throttle on my MPI. It only really sticks when the throttle is visibly closed and manifests itself by giving TPS readings that indicate the throttle is not closed to the ECU. i.e. Throttle position is read as 5+ and the throttle switch is shown as "ON" on my ACR 4. This causes it to struggle to start cleanly without me blipping the accelerator to open the throttle.

 

If I give the springs on the throttle body a spray of WD40 and move the throttle through it's motion a few times then I can get it to return so that a value of ~4 is typically read on the ACR4 but this only lasts a few days. It seems that potentially being a bit colder makes it worse.

 

I've verified that the accelerator cable sticking isn't causing it as I've loosened it off and the problem still exists. There is an adjuster screw, can I just tweak this to increase the 'stop' position? What should a typical 'minimum' i.e. throttle closed TPS reading from the ACR4 be? I've only ever seen mine go down to ~4.



#2 tmsmini

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Posted 24 October 2018 - 09:47 PM

Do not adjust the screw.

If the cable is not sticking and it is adjusted properly, then most likely the throttle body is sticking. This can be fixed by very light sanding to relieve the area where the butterfly is sticking. Or a new Burlen throttle body can be purchased.

Terry



#3 kangaroomadman

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Posted 25 October 2018 - 08:17 PM

You mean sanding the inside of the body rather than the butterfly? Given the cost of a new throttle body, I am considering trying the sanding method.

 

Do you know what minimum value should be read from the TPS? So I know when I've managed to get it fully shut.



#4 Kubbar

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Posted 26 October 2018 - 08:42 AM

Hello 

 

the standard throttle position on acr4 for MPI should be: 5.0 adjust it under this no.

i have uploaded a video to help you

 

 

 

regards,



#5 tmsmini

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Posted 26 October 2018 - 05:06 PM

If you press and hold the OK button while the throttle position is highlighted, then the ACR will show this value:

Throttle Position Strategy throttle position (in ° ) dependent on pedal position, expect 4.5°  upwards

 

This is true for all the settings in the ACR4



#6 viz139

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Posted 26 October 2018 - 09:31 PM

Assuming that the throttle not closing problem is manifesting itself as possably an erratic or high idle have you checked the idle air control valve is clean . The ECU may be holding the throttle open to aid idle.



#7 tmsmini

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Posted 27 October 2018 - 04:26 PM

I would really try to verify the issue before making any adjustments.

I think you would need to remove the throttle body and clean it to make sure it is the cause of the issue. The IAC valve also probably could use cleaning.

With the throttle body off of the intake, you should be able to see if and where it is sticking. The plastic throttle bodies can warp over time, but as mentioned above usually show up as a high idle.



#8 kangaroomadman

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Posted 27 October 2018 - 04:46 PM

Thanks for the tip on the ACR4! I never knew you could do that.

When the TPS reading is higher than 5 on startup it does give a high idle so it is sounding like a warped throttle body.

#9 kangaroomadman

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Posted 14 November 2018 - 08:18 PM

So I bit the bullet and replaced the throttle body with a new Burlen 52mm one and that solved the sticking issue. Since then I've had a bit of a lumpy idle and looking at the readings on my ACR4 noticed that the stepper position frequently gets down to 0 so no further adjustment available.

 

This evening I followed the 'Stepper Adjust' process on my ACR4 and by adjusting the throttle stop screw managed to get the stepper position to a value of 20 with a nice idle. The ACR4 then asked me if I wanted to 'Reset the adaptive values' to which I said 'OK' and then the engine just died! Not sure if this is meant to happen or not. I then restarted the engine and the idle was lumpy again with a stepper position of 0! I proceeded to tinker further and tried to follow the 'Stepper Adjust' again but any movement of the screw either threw the stepper to ~35 and a high idle or down to 0 again so I gave up on this process and did it manually by just looking at the raw stepper position value.

 

Once I'd finished it was hovering around 18 which is OK for now but I may tweak more. I'll see how it runs on my drive to work tomorrow.

 

I do wonder if there is a small air leak somewhere as once I had the air box back on I tried to cover the inlet with my hand but there was no noticeable change in tone of the engine.



#10 kangaroomadman

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Posted 15 November 2018 - 08:33 AM

It didn't hit 0 this morning but once I pulled up the stepper position was dropping down whilst it was idling. When I switched off the stepper was on about position 5 with MAP at around ~31. Presumably the stepper position would've dropped further at this point.

 

The adjustment I made on the screw last night was pretty much to back it right out so the butterfly is coming to a natural stop instead of hitting the screw. Surely this means that hardly any air is going to get through here and that coupled with a low stepper position indicates an air leak?

 

I don't believe I had an air leak before I switched the throttle body so presumably the culprit is likely to be leaking underneath the throttle body?



#11 tmsmini

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Posted 15 November 2018 - 03:20 PM

Did you clean the IAC valve and check the hoses connected to it?

A new TB should already be adjusted to where it is in range for the IAC to manage idle.



#12 kangaroomadman

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Posted 15 November 2018 - 03:24 PM

The hoses looked OK but I'll double check them.

I haven't cleaned the IACV - How does one 'clean' it?



#13 tmsmini

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Posted 15 November 2018 - 04:20 PM

Just take it off and spray with carb cleaner or TB spray cleaner. The wipe out the residue. Careful with the O rings that are used to seal it to the intake and housing.
iacv-01.jpg


Edited by tmsmini, 15 November 2018 - 04:21 PM.


#14 kangaroomadman

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Posted 15 November 2018 - 10:46 PM

Took it off this evening to give it a clean. There was a bit of black residue but not a huge amount.

While it was off I thought I’d double check the operation and that it was moving when the ignition is turned on/off. So I turned the ignition on/off and it was moving but of course it tries to move to the maximum position and which is fine when there is an end stop, however, when it’s not fitted it means the post, spring and all fly off in to the pitch black engine bay! DOH!

I found all the bits and re-assembled everything and just went for a quick spin. Idle is quite bad but it’s possibly still learning? Will see how it fares tomorrow.

#15 kangaroomadman

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Posted 16 November 2018 - 09:26 AM

Idle was better this morning but the stepper was still hovering around 0 once I pulled up at work.

 

I'm assuming position 0 is fully closed, and the TB is adjusted to pretty much be as closed as possible so where's the inlet air coming from?






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