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Volkswagen Jetta, Golf, GTI: 1985-1992 (A2) poor driveability when cold- 1985 vw gti


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Last Post: Jun 29, 2014 7:44 PM Last Post By: tcovenant2000
stark14

Posts: 1
Registered: 06/29/14
poor driveability when cold- 1985 vw gti
Posted: Jun 29, 2014 2:08 PM
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Guys:

Have been all over this CIS-E system and I have a poor after start driveability, hesistation, poor idle, then it smooths out when warm. Here's what I have done:
Static fuel pressure: 79 psi
Differential pressure (static) 76 psi
O2 module wiring check: all circuits with specs per bentley manual
Idle speed control (new): set at 24 degrees dwell
Diff current set at 10 milliamps at idle
New transfer pump and fuel filter
Rebuilt fuel distributor
New injectors
Secondary tune-up with base timing set
All grounds cleaned
New coolant temp sensor
New O2 sensor

With engine running, I am monitoring fuel pressure from the test port and I have discovered that the system pressure is low, 68 psi, then will come up to 76 psi, during the time of the sluggishness and virtually no fast idle. Just for grins, I applied a vacuum pump to the fuel pressure regulator vacuum port and I found gasoline in the vacuum port! From my experience with american built vehicles, this a big "no-no!" Could this be a contributing factor to the "lack of a fast idle and poor performance" when cold? Open to all suggestions at this time!
Thanks,
Jeff
tcovenant2000

Posts: 1,761
Registered: 12/09/03
Re: poor driveability when cold- 1985 vw gti
Posted: Jun 29, 2014 7:44 PM   in response to: stark14 in response to: stark14
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Yes. Means you've got a broken diaphragm. This prevents the vacuum regulator from doing its job, causing rough idle. In addition it means you're getting unmetered fuel during idle. Maybe or maybe not related to your initial complaint.
Have you tried disconnecting the O2 sensor, then let it sit overnight and see if the cold idle/run problem goes away? I don't remember if CIS-E has a CTS or (more likely) a Lambda Temp sensor. If it's the latter, that's likely what's wrong. It's not telling the ECU that the engine is cold, so the ECU is monitoring the O2 sensor. It's also preventing the system from engaging the cold enrichment. If that's true then disconnecting the O2 will make the cold run problem go away. Then you'll know you need to replace the sensor.

Thomas

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