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Throttle Not Fully Returning


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#16 Bat

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Posted 16 November 2018 - 11:43 AM

Hi,

Can you measure the voltage from the throttle pot?

Test equipment doesn't always tell the truth...

Cheers  :proud:



#17 viz139

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Posted 16 November 2018 - 12:41 PM

At idle the air comes through the Idle Air Control Valve. 



#18 Bat

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Posted 16 November 2018 - 01:18 PM

At idle the air comes through the Idle Air Control Valve. 

 

It does, but he's said the valve is at 0 position, which if correct means it's fully shut.



#19 tmsmini

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Posted 16 November 2018 - 05:04 PM

The Burlen TB would have come with a new TPS, but it would not hurt to test it. I am not sure how the MEMS 2J measures the "stepper" steps, but it involves the TPS in the adjustment mode of an ACR4. After that it must use the stored value and that is why it should not be adjusted unless you have to tool to set it properly.


Edited by tmsmini, 16 November 2018 - 08:24 PM.


#20 viz139

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Posted 16 November 2018 - 08:42 PM

 

At idle the air comes through the Idle Air Control Valve. 

 

It does, but he's said the valve is at 0 position, which if correct means it's fully shut.

 

Just to be sure is the throttle position sensor at 0 or the Idle control valve. 



#21 kangaroomadman

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Posted 16 November 2018 - 09:01 PM

The IACV goes to zero on hot idle and then it gets a bit lumpy. TPS is ~4.5 degrees.

I’ll squirt some carb cleaner around tomorrow morning to see if I can find a leak. I’ll also see if I can get my multimeter on the TPS but the readings from the ACR4 seem plausible: ~4.5 degrees closed and ~90 degrees fully open. And smooth inbetween. Not sure how the ACR4 could make that up.

#22 tmsmini

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Posted 17 November 2018 - 03:46 AM

So if the ACR4 is reading 0 for the stepper position when it suggests:

14. Stepper Position Stepper motor position in steps, depends on idle control requirements, more steps indicate greater level of control

 

I would check the wiring for chafing as that does not seem correct. I think the cabling for the IACV loops around the back of the air cleaner bracket and it supposed to be attached, sometimes people leave this off and it is routed where it can make contact.

 

Checking for other leaks makes sense as well, if indeed that is a valid IACV step position.



#23 kangaroomadman

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Posted 17 November 2018 - 09:28 AM

I couldn't find my multimeter so that ruled out testing the TPS.

 

I warmed up the engine and sprayed around some carb cleaner around the various sensors etc. mounted on the inlet manifold but there was no noticeable engine tone change. Spraying in to the TB did change the engine note as expected. So possibly no leaks on the manifold itself?

 

The stepper position was around 8 this morning once it had settled so a little higher than before. I popped off the IACV rubber pipe from the TB end and covered with my finger - this caused the revs to drop to ~800 and the stepper position increased to 60 to try and account for the loss in airflow. Releasing my finger spiked the revs and then the stepper position dropped down again.

 

I then looked at some of the other intake components on the inlet manifold and interestingly I think quite a bit of air is coming in via the crankcase ventilation system. I blocked off the hose and the stepper adjusted by ~+20 to account for this. Is this normal?

 

The car is off to the garage this afternoon for some welding prior to an MOT next week, so hopefully it behaves for the tester.



#24 minimat

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Posted 17 November 2018 - 12:41 PM

Didnt some of these have a plastic throttle body that would cause the throttle to stick?



#25 kangaroomadman

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Posted 17 November 2018 - 12:44 PM

Yep, I’ve replaced my plastic throttle body that was sticking and now my stepper position goes to zero although it does seem to be improving.

#26 viz139

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Posted 17 November 2018 - 01:42 PM

Just remembered another problem I had with an MPi, air getting in around the servo pipe where it pushes into the manifold. Remove the pipe and block the hole to test.



#27 tmsmini

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Posted 17 November 2018 - 03:37 PM

The purge valve can be an issue, as the crankcase ventilation system goes to a holding tank under the fender, then at certain times the valve opens to release the fumes into the inlet. If this sticks open, it could cause an issue.

Terry



#28 leepol83

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Posted 17 December 2020 - 11:07 PM

Hi a few years ago🙈 but did this get sorted ?

#29 pete l

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Posted 18 December 2020 - 07:55 AM

It does sound a lot like your problem.


Edited by pete l, 18 December 2020 - 07:55 AM.





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