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Cold Bus Requires Revving to Warm
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keithferraro
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PostPosted: Tue May 22, 2018 7:07 pm    Post subject: Cold Bus Requires Revving to Warm Reply with quote

The Bus- 79 Fuel Injected
Assumptions, Mechanically sound ignition, FI, Timing, etc.

Before mentioning that I should have found this topic in an old thread, I honestly tried hard and couldn't find it anywhere. A little CSV talk,etc. but not this specifically....

Bus starts very well (indicating working cold start valve), then tries to stall around the 5-8 second mark, you rev to revive, 5-8 seconds, repeat. At the 1-2 minute mark (right after you finish rolling your cigarette, per Muir) the bus idle will drop but not quite stall and it will idle fine permanently from there. The bus runs fine once warm. It's trivial, I don't mind revving but I'd like for it run as it were mechanically intended. I don't believe that it's the cold start valve, nor the thermo-time switch as it fires up well when cranking.
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Tcash
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PostPosted: Tue May 22, 2018 7:26 pm    Post subject: Re: Cold Bus Requires Revving to Warm Reply with quote

Auxiliary Air Regulator (AAR)
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keithferraro
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PostPosted: Tue May 22, 2018 8:12 pm    Post subject: Re: Cold Bus Requires Revving to Warm Reply with quote

Thanks Tcash. Not sure how I missed that. subsequent reading has me agreeing with you. I've got some testing to do, and probably some searching at the junkyard. Thanks!
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Tcash
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PostPosted: Tue May 22, 2018 8:33 pm    Post subject: Re: Cold Bus Requires Revving to Warm Reply with quote

https://www.busdepot.com/049133453-42
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aeromech
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PostPosted: Tue May 22, 2018 8:39 pm    Post subject: Re: Cold Bus Requires Revving to Warm Reply with quote

Pull the AAR and place on the bench. Look down the throat. You should see an open window. Apply 12 volts to the two pins and watch the window close down. Let it cool and watch the window open back up. Pretty simple to test
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PostPosted: Tue May 22, 2018 10:46 pm    Post subject: Re: Cold Bus Requires Revving to Warm Reply with quote

The AAR is VERY similar to cracking the throttle open, so good advice there. A multimeter test of the TS2 cold and warm would be wise too. You should have 250-400 ohms fully warmed up, 2000-3000 ohms on a summer morning before your first start, and above 5000 ohms when below freezing. It should be snug in the mount, but not corroded, and the wire connection should be clean and free of broken wire strands.

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jtauxe Premium Member
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PostPosted: Wed May 23, 2018 6:18 am    Post subject: Re: Cold Bus Requires Revving to Warm Reply with quote

keithferraro wrote:
Bus starts very well (indicating working cold start valve), then tries to stall around the 5-8 second mark, you rev to revive, 5-8 seconds, repeat. At the 1-2 minute mark (right after you finish rolling your cigarette, per Muir) the bus idle will drop but not quite stall and it will idle fine permanently from there.

This is one notable piece of advice that has been debunked. If you look in your VW owner's manual, it says that you should not rev it to warm up (as this is when the engine is cold and experiences the most wear), but rather that you should get it started and drive off right away. That will warm it even faster, reducing the time of running in a cold state.
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SGKent Premium Member
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PostPosted: Wed May 23, 2018 7:17 am    Post subject: Re: Cold Bus Requires Revving to Warm Reply with quote

the bus was designed to get in and drive away (as John said see owner's manual). If it fails to do that then do a full tune up and check for vacuum leaks. Don't believe everything Muir wrote. It is dated and more toward the days of the split or early bug.
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Tcash
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PostPosted: Wed May 23, 2018 7:42 am    Post subject: Re: Cold Bus Requires Revving to Warm Reply with quote

Sometimes u can clean them. Do a search there is a good thread.
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