91 Jetta Rough start

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Let me start by saying I am fairly novice at auto repair and I won't pretend to know more than I do.

With that out of the way here's my issue I have a 1991 VW Jetta, 1.8 L automatic with 125k miles. All the recommended maintenance is completed at the recommended intervals. For the past few days, when I start my car (after sitting for more than four hours), the engine revs itself four or five times usually from idle to 1500-2000 RPM then smooths out. If the car hasn't been sitting long, this doesn't happen.
Being a novice, I checked the rotor and distributor cap. I noticed some build-up so I changed them (my level of know-how ) ) even though they only have under 10k on them. No difference was made. I am wondering whether changing the plugs and the cables will do anything or I'm barking up the wrong tree.
Please advise other diagnostics I might run. Thanks!

posted by  vwfreak

Paper, CD, the info is all the same. I personally prefer book in hand but this is the 21st century and have gotten used to going to the computer. I'd have to put up new buildings to hold the books I would need to take the place of my AllData. Progress marches on. 8)

posted by  vwhobo

Not likely an ignition problem. Sounds suspiciously like a vacuum leak that goes away. First try looking at the auxilary air regulator. It is essentially a device that gives you a controlled vacuum leak to raise idle speed during warm-up (very rough description). Also look at the intake duct between the airflow sensor and the throttle body. Check specifically for cracks on the underside. Any leak here can cause this to occur also.

If you don't have a manual get one now, it'll show you where the aux regulator is and how to test it. Robert Bentley is the best for VW's, they made the factory service manuals. At least pop for a Haynes manual. For your car you need #884, probably around $15 at your friendly local parts house.

Good luck and let me know what you find.

posted by  vwhobo

Thank you sir! I have the Haynes book - I'll check to see how it addresses your instructions. If it doesn't, I've heard great things about Bentley's. Maybe now's the time to upgrade. BTW, do you know if the Bentely's CD-ROM is preferred? It's all they have for my 2002 Eurovan. Take care.

posted by  vwfreak

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