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Banish a little rust a day people
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5,306 Posts
Discussion Starter · #1 · (Edited)
As the title says, I have an intermittent issue where my idle comes up to 1500rpm and sits there. If I press the clutch in and hold it down it drops back to normal. It doesn't try to maintain 1500rpm when driving, it'll smoothly drive at below that in slow traffic if need be. When coasting in neutral with the clutch up it also doesn't do it. Car is a 2001 mk2.5 1.8l VVT. Engine all stock.

Things it definitely isn't:
  • MAF
  • cam sensor
  • crank sensor
  • coils
  • plugs
  • Tps
  • Icv
 
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Hiding from the Ayatollah or making Full Metal Jac
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1,751 Posts
Clean the Idle control valve ?
 

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Banish a little rust a day people
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5,306 Posts
Discussion Starter · #3 ·
Not the icv or tps. Will update
 

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Hiding from the Ayatollah or making Full Metal Jac
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1,751 Posts
have you properly cleaned your throttlebody ?

how taught is your throttle cable ?
 

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Banish a little rust a day people
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5,306 Posts
Discussion Starter · #5 ·
Wouldn't explain the clutch behaviour. I suspect it might be the box neutral switch
 

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Happily expanding the To Do list since 1997
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10,688 Posts
Coasting in neutral it doesn't do it, sitting stopped in neutral it does? That's strange.

I guess there are several things which can tell the ECU to expect extra load so raise the idle a little (higher fan settings, aircon on) but even if it was getting a bogus message about one of those, why would pressing the clutch fix it?

I think I see what you're saying about the neutral switch: if that's failed/intermittent the ECU might think the car's still in gear and raise the idle to catch it before it stalls. Seems like a good thing to check first.
 

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Banish a little rust a day people
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5,306 Posts
Discussion Starter · #7 ·
Coasting in neutral it doesn't do it, sitting stopped in neutral it does? That's strange.

I guess there are several things which can tell the ECU to expect extra load so raise the idle a little (higher fan settings, aircon on) but even if it was getting a bogus message about one of those, why would pressing the clutch fix it?

I think I see what you're saying about the neutral switch: if that's failed/intermittent the ECU might think the car's still in gear and raise the idle to catch it before it stalls. Seems like a good thing to check first.
yeh, I know the ECU looks are tps position, neutral switch and clutch pedal switch for idle, but if it also looks at speed then it would explain the coasting behaviour.
 
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