pepem
Member Since: 24 Oct 2021
Location: Devon
Posts: 13
  
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My Disco 3 V8 occasionally has a surging idle. Starts up fine, revs up to about 1000rpm and then falls to normal idle at around 7/8 hundred rpm but then surges up and down for a while. Any ideas on the cause?
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 26th Mar 2022 9:49 pm |
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kajtzu
Member Since: 11 Aug 2017
Location: Helsinki
Posts: 6577
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Some ideas.
1. Read the codes
2. Change engine air filter unless new (cheap)
3. Clean mass airflow sensor (if it looks gunked)
4. Clean throttle body
My money is on the throttle body. 
Do let us know the root cause once you find it. 
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| 26th Mar 2022 10:23 pm |
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pepem
Member Since: 24 Oct 2021
Location: Devon
Posts: 13
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Had a go this morning, checked the air filter which looked okay but had quite a bit in the pleats. then on further inspection found that the air box wasn’t connected properly to the inlet from the front wing so was full of leaves ect. Checked the mass air sensor and throttle body too. Didn't look too bad but think ill give them a clean anyway just to be safe. Anyway, re assembled it all and it was idling perfectly. Just need to fing the torqx screw I dropped of the sensor now  Thank you for your help.
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| 27th Mar 2022 5:29 pm |
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kajtzu
Member Since: 11 Aug 2017
Location: Helsinki
Posts: 6577
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| 27th Mar 2022 10:09 pm |
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tgreer
Member Since: 12 Aug 2020
Location: Henley-on-Thames
Posts: 110
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My V8 does this and then seems to level out after you start driving/apply load then release. Never worked out why.
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| 31st Mar 2022 2:16 pm |
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MintyHit
Member Since: 25 Jul 2017
Location: Bradford on Avon
Posts: 227
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Cleaning the mass airflow sensor fixed mine.
It could also be valve clearances but that's a big job.
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| 31st Mar 2022 3:08 pm |
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pepem
Member Since: 24 Oct 2021
Location: Devon
Posts: 13
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When cleaning the throttle body do i need to worry about moving the flange. Said in one of the videos if you moved it you'd have to get it reset by the dealer but surely you need to move it to clean it thoroughly?
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| 1st Apr 2022 12:01 pm |
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MintyHit
Member Since: 25 Jul 2017
Location: Bradford on Avon
Posts: 227
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The MAF is located just after the airbox to the left.
Does the throttle body need cleaning as well? I guess if you are worried about calibration you could ask someone to step on the accelerator with the ignition on and see if the butterfly opens.
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| 1st Apr 2022 1:00 pm |
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pepem
Member Since: 24 Oct 2021
Location: Devon
Posts: 13
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I think it would be worth cleaning it. Checked just now and there's a noticeable build up around the edges.
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| 1st Apr 2022 1:11 pm |
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