Home Technical Discussions Volkswagen Jetta, Golf, GTI: 1993-1999, Cabrio 1995-2002 (A3)

Volkswagen Jetta, Golf, GTI: 1993-1999, Cabrio 1995-2002 (A3) 1993 Cabrio runs very rough, will not idle


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Last Post: Jan 30, 2013 11:41 PM Last Post By: tcovenant2000
Anacortes_Auto

Posts: 1
Registered: 01/29/13
1993 Cabrio runs very rough, will not idle
Posted: Jan 29, 2013 6:08 PM
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Hi guys,
As the subject line states, I'm working on a 1993 cabrio and I'm having some difficulty pin pointing the issue.

The car was towed into the shop and was at first a crack no start. After replacing the ECM, Distributor and the ECM coolant sensor and checking the timing I am stuck with a poor Idle condition. The car does have a quite noticable exhaust leak, which I believe to be part of the problem but not lone culprit. When I take it to 2000rpm the idle will start hunting, checked for vaccum leaks and the Idle stabilizer. No leaks found and the idle stabilizer has power and is working as designed.

Anybody here run into a similiar issue? Any feedback will be helpfull
tcovenant2000

Posts: 1,802
Registered: 12/09/03
Re: 1993 Cabrio runs very rough, will not idle
Posted: Jan 30, 2013 11:41 PM   in response to: Anacortes_Auto in response to: Anacortes_Auto
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Start by disconnecting the O2 sensor. If the idle is noticeably smoother then either the O2 sensor is suspect or, more likely, the exhaust leak is allowing ambient air to contact the sensor end of the O2 sensor. This causes over-riching of the fuel mixture which causes the idle to shift. Since the amount of air reaching the O2 sensor will vary depending on RPM, the shift in idle causes the condition to change and dropping the idle back down.
By disconnecting the O2 sensor you force the system into open loop mode and no fuel mix adjustment is made.
That test is only valid on a fully warmed car, though, so make sure she's at temp before you try it.

The other likely suspect is a vacuum leak of some sort.

Thomas

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