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Frank G
Samba Member
Joined: March 16, 2004
Posts: 8
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 Posted: Tue Aug 10, 2021 12:19 pm Post subject: MK2 digifant jetta, high idle, weird situation |
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1990 vw mk2 8v with digifant injection.
Car was running OK, installed a large stereo which involved disconnecting battery terminals, and welding a grounding bolt in the trunk. I reconnect the cables to the battery, start the car, and the idle is immediately at 1800-2000.
The idle screw is there, and when plugged, idle does not drop. I pinch the Idle Speed valve hose and idle immediately drops. I disconnect the wiring to the idle valve (two pins, not three), and no change to the idle (think makes sense since the idle is so high the ISV should not be receiving any voltage.) Throttle cable is not tight. idle switch clicks when moving the throttle off of idle position (car off so I can hear the switch)
The drop in idle speed when pinching the ISV hose leads me to think it is leaking air into the engine, past the throttle plate.
Any thoughts? |
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TDCTDI
Samba Advocatus Diaboli
Joined: August 31, 2013
Posts: 12860
Location: North Carolina
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| Posted: Tue Aug 10, 2021 12:31 pm Post subject: Re: MK2 digifant jetta, high idle, weird situation |
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Tap on the ISV with a wrench, they sometimes stick open.
_________________
Everybody born before 1975 has a story, good, bad, or indifferent, about a VW.
GOFUNDYOURSELF, quit asking everyone to do it for you!
An air cooled VW will make you a hoarder.
Do something, anything, to your project every day, and you will eventually complete it. |
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Frank G
Samba Member
Joined: March 16, 2004
Posts: 8
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| Posted: Wed Aug 11, 2021 4:46 am Post subject: Re: MK2 digifant jetta, high idle, weird situation |
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| TDCTDI wrote: |
| Tap on the ISV with a wrench, they sometimes stick open. |
Great suggestion. I did that and no change. I then disassembled the bad one I have to see how it works and there is a small o-ring inside that might have failed. that would allow air to bypass the valve for sure. Ordering a new one today but I think something else is wrong. I swapped over a believed to be good idle valve that clicks when powered up, and it still idles very high.
Could ignition timing be advanced via the ECU as a result of welding with the battery cables disconnected? |
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TDCTDI
Samba Advocatus Diaboli
Joined: August 31, 2013
Posts: 12860
Location: North Carolina
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| Posted: Wed Aug 11, 2021 5:18 am Post subject: Re: MK2 digifant jetta, high idle, weird situation |
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I would look for a vacuum leak somewhere. When a Digifukt ECM goes bad, it usually goes full dump on the injectors & will fill the block with the contents of the fuel tank.
_________________
Everybody born before 1975 has a story, good, bad, or indifferent, about a VW.
GOFUNDYOURSELF, quit asking everyone to do it for you!
An air cooled VW will make you a hoarder.
Do something, anything, to your project every day, and you will eventually complete it. |
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timvw7476
Samba Member
Joined: June 03, 2013
Posts: 2206
Location: seattle
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| Posted: Wed Aug 18, 2021 5:32 pm Post subject: Re: MK2 digifant jetta, high idle, weird situation |
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| check the bolts holding the intake on, there are six, most are hidden. Should be 6mm allen head, they like to vibrate loose & fall out. |
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Frank G
Samba Member
Joined: March 16, 2004
Posts: 8
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| Posted: Thu Aug 19, 2021 5:57 am Post subject: Re: MK2 digifant jetta, high idle, weird situation |
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Definitely a great suggestion on the intake manifold bolts.
The issue remains that the air is passing through the idle valve even when powered OFF. I checked this by clamping the idle valve hose shut and the idle slowed down.
This makes me think the o-ring inside has failed, or the return spring pushing the valve closed is weak. I ordered a new one, i will report the effect.
I need to pull the intake manifold anyway, I plant to find the leaking injector and put on a new gasket. |
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