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AndyC13
Samba Member
Joined: December 30, 2014
Posts: 56
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 Posted: Tue Sep 11, 2018 7:01 am Post subject: High idle revs when "cold" |
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For the last few months, ever since changing a heat exchanger, fitting a Vintage Speed exhaust, and setting valves/timing, my idle revs when the engine is "cold" have been high.
The engine is a 1979 2000cc CA FI Type 4 engine.
I have been told to look at the following things.
1) Check the one way valve on the brake servo hose is functioning
2) Check the decel valve is working
3) Check the FI system using a multimeter
Any other advice? |
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Randy in Maine
Samba Member
Joined: August 03, 2003
Posts: 34890
Location: The Beach
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| Posted: Tue Sep 11, 2018 7:05 am Post subject: Re: High idle revs when "cold" |
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I would have a good look at the aux air regulator. That vacuum hose to the S boot likes to split at the little 90º bend at the bottom.
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airschooled
Air-Schooled
Joined: April 04, 2012
Posts: 12721
Location: on a bike ride somewhere
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| Posted: Tue Sep 11, 2018 7:07 am Post subject: Re: High idle revs when "cold" |
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Got an actual RPM number for us?
A high mileage engine with a functioning AAR can go as high as 1,500 RPM on first start before calming down as it warms up.
Robbie
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AndyC13
Samba Member
Joined: December 30, 2014
Posts: 56
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| Posted: Tue Sep 11, 2018 7:12 am Post subject: Re: High idle revs when "cold" |
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| asiab3 wrote: |
Got an actual RPM number for us?
A high mileage engine with a functioning AAR can go as high as 1,500 RPM on first start before calming down as it warms up.
Robbie |
I don't I'm afraid.
All I can describe it as is feeling awkward at traffic lights with the engine revving away! |
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AndyC13
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Joined: December 30, 2014
Posts: 56
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| Posted: Tue Sep 11, 2018 7:13 am Post subject: Re: High idle revs when "cold" |
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| Randy in Maine wrote: |
I would have a good look at the aux air regulator. That vacuum hose to the S boot likes to split at the little 90º bend at the bottom.
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Cheers
Gives me something else to check out. |
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airschooled
Air-Schooled
Joined: April 04, 2012
Posts: 12721
Location: on a bike ride somewhere
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| Posted: Tue Sep 11, 2018 7:19 am Post subject: Re: High idle revs when "cold" |
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Make sure the distributor gets oiled down the shaft beneath the rotor every oil change. Normally a few drops is enough, but if it’s been ignored for a while, I make sure to get a tablespoon or so of oil down the hole. No spilling!!
The advance mechanism in the distributor can stick and cause timing to hang up too advanced.
Robbie
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calo1956
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Joined: April 18, 2011
Posts: 699
Location: long Island new york
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| Posted: Tue Sep 11, 2018 7:40 am Post subject: Re: High idle revs when "cold" |
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Just to add to Randys comment, I had that AAR boot out, and didn't even see the split in it till i looked really carefully. Not having access to a new one and wanting to eliminate two very hard to reach hose clamps, i just eliminated it, and ran a hose directly to the S boot, it was a little funky, but it worked.
Funny, iI have the opposite problem of low idle till it warms up.
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AndyC13
Samba Member
Joined: December 30, 2014
Posts: 56
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| Posted: Tue Sep 11, 2018 7:40 am Post subject: Re: High idle revs when "cold" |
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| asiab3 wrote: |
Make sure the distributor gets oiled down the shaft beneath the rotor every oil change. Normally a few drops is enough, but if it’s been ignored for a while, I make sure to get a tablespoon or so of oil down the hole. No spilling!!
The advance mechanism in the distributor can stick and cause timing to hang up too advanced.
Robbie |
In the 4 and 1/2 years I've had the bus, I've never done this and this is the first I've heard of it!
I'll be sure to give this a go too. |
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Abscate
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Joined: October 05, 2014
Posts: 22639
Location: NYC/Upstate/ROW
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| Posted: Tue Sep 11, 2018 7:57 am Post subject: Re: High idle revs when "cold" |
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| AndyC13 wrote: |
| asiab3 wrote: |
Make sure the distributor gets oiled down the shaft beneath the rotor every oil change. Normally a few drops is enough, but if it’s been ignored for a while, I make sure to get a tablespoon or so of oil down the hole. No spilling!!
The advance mechanism in the distributor can stick and cause timing to hang up too advanced.
Robbie |
In the 4 and 1/2 years I've had the bus, I've never done this and this is the first I've heard of it!
I'll be sure to give this a go too. |
I wonder if lubricating the distributor fell off the service map after they went to Hall Effect Ignition systems?
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airschooled
Air-Schooled
Joined: April 04, 2012
Posts: 12721
Location: on a bike ride somewhere
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| Posted: Tue Sep 11, 2018 7:59 am Post subject: Re: High idle revs when "cold" |
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| Abscate wrote: |
I wonder if lubricating the distributor fell off the service map after they went to Hall Effect Ignition systems? |
Negative, the distributor still has advance weights and springs that need it. VW wouldn’t have deleted it, but other shops might have “forgotten.”
Robbie
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Randy in Maine
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Joined: August 03, 2003
Posts: 34890
Location: The Beach
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AndyC13
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Joined: December 30, 2014
Posts: 56
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| Posted: Tue Sep 11, 2018 9:19 am Post subject: Re: High idle revs when "cold" |
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I found that page earlier, but all the photos have dropped off! |
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AndyC13
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Joined: December 30, 2014
Posts: 56
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| Posted: Thu Sep 13, 2018 8:33 am Post subject: Re: High idle revs when "cold" |
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1) From what I can see, all hoses are connected.
2) The decel valve is definitely functioning. Tested an alternative way and still shows as working.
3) AAR elbow hose is not split. Cracking, but not split enough to matter.
4) One-way brake servo hose valve is working. Checked that.
The timing appeared slightly out (by one degree) and I have altered the idle speed as it has always been a bit high.
Interestingly, and I don't know if it matters, but when the bus is started from cold, the idle speed is fine. It's only after the accelerator has been touched for the first time that the high idle speed starts.
My next step is to test the ECU wiring with a multimeter. |
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airschooled
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| Posted: Thu Sep 13, 2018 8:37 am Post subject: Re: High idle revs when "cold" |
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Does the engine eventually calm down when warmed up? If so, test and adjust your AAR.
Have you tried adjusting the idle speed screw on a fully warmed up engine to 900-1000 RPM and seeing where the cold idle falls next morning?
Robbie
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AndyC13
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Joined: December 30, 2014
Posts: 56
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| Posted: Thu Sep 13, 2018 8:42 am Post subject: Re: High idle revs when "cold" |
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| asiab3 wrote: |
Does the engine eventually calm down when warmed up? If so, test and adjust your AAR.
Have you tried adjusting the idle speed screw on a fully warmed up engine to 900-1000 RPM and seeing where the cold idle falls next morning?
Robbie |
After 10-15 minutes of driving the idle is perfect! Literally only for the part where it's "cold".
I need to get a tachometer and do it properly, as doing it by ear isn't ideal! |
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airschooled
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Joined: April 04, 2012
Posts: 12721
Location: on a bike ride somewhere
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| Posted: Thu Sep 13, 2018 8:47 am Post subject: Re: High idle revs when "cold" |
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| AndyC13 wrote: |
| asiab3 wrote: |
Does the engine eventually calm down when warmed up? If so, test and adjust your AAR.
Have you tried adjusting the idle speed screw on a fully warmed up engine to 900-1000 RPM and seeing where the cold idle falls next morning?
Robbie |
After 10-15 minutes of driving the idle is perfect! Literally only for the part where it's "cold".
I need to get a tachometer and do it properly, as doing it by ear isn't ideal! |
Your ear will suffice nicely!
Run this test next time your engine is cold-idling too fast:
Pinch off the hose to the AAR (with vise grip jaws wrapped in electrical tape as not to damage the hose) and make sure the idle drops. Drop? Good! Adjust AAR. No drop? Interesting we can discuss it more later.
Robbie
EDIT: check the AAR for approximately 30 ohms across the terminals too. The more resistance, the longer it takes to close down and give you a normal hot idle. Performance engine folks take note, that a 20-ohm resistor in-line will slow your AAR closing speeds to accommodate your engine deviance.
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AndyC13
Samba Member
Joined: December 30, 2014
Posts: 56
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| Posted: Thu Sep 13, 2018 8:57 am Post subject: Re: High idle revs when "cold" |
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| asiab3 wrote: |
| AndyC13 wrote: |
| asiab3 wrote: |
Does the engine eventually calm down when warmed up? If so, test and adjust your AAR.
Have you tried adjusting the idle speed screw on a fully warmed up engine to 900-1000 RPM and seeing where the cold idle falls next morning?
Robbie |
After 10-15 minutes of driving the idle is perfect! Literally only for the part where it's "cold".
I need to get a tachometer and do it properly, as doing it by ear isn't ideal! |
Your ear will suffice nicely!
Run this test next time your engine is cold-idling too fast:
Pinch off the hose to the AAR (with vise grip jaws wrapped in electrical tape as not to damage the hose) and make sure the idle drops. Drop? Good! Adjust AAR. No drop? Interesting we can discuss it more later.
Robbie
EDIT: check the AAR for approximately 30 ohms across the terminals too. The more resistance, the longer it takes to close down and give you a normal hot idle. Performance engine folks take note, that a 20-ohm resistor in-line will slow your AAR closing speeds to accommodate your engine deviance. |
Will do. Cheers  |
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Abscate
Samba Member
Joined: October 05, 2014
Posts: 22639
Location: NYC/Upstate/ROW
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| Posted: Thu Sep 13, 2018 9:08 am Post subject: Re: High idle revs when "cold" |
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| asiab3 wrote: |
| Abscate wrote: |
I wonder if lubricating the distributor fell off the service map after they went to Hall Effect Ignition systems? |
Negative, the distributor still has advance weights and springs that need it. VW wouldn’t have deleted it, but other shops might have “forgotten.”
Robbie |
Im wondering if when
Adjust points
fell off the owner manual due to Hall effect
was
Lube Hall effect distributor
added?
Any VW mechanic adjusting/replacing points would lube the distributor of course.
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SGKent 
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Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
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| Posted: Thu Sep 13, 2018 9:24 am Post subject: Re: High idle revs when "cold" |
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put a tach on it and watch it for 5 minutes after starting the bus. Tell us where it is when it starts and at each appx minute. Please don't tell us you don't have a tach because you said idle was perfect and you would need a tach to know that. You don't need a tach up front, just the one that you use to tune it. Let it idle for 5 minutes from cold and report back.
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AndyC13
Samba Member
Joined: December 30, 2014
Posts: 56
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| Posted: Thu Sep 13, 2018 9:26 am Post subject: Re: High idle revs when "cold" |
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| SGKent wrote: |
| put a tach on it and watch it for 5 minutes after starting the bus. Tell us where it is when it starts and at each appx minute. Please don't tell us you don't have a tach because you said idle was perfect and you would need a tach to know that. You don't need a tach up front, just the one that you use to tune it. Let it idle for 5 minutes from cold and report back. |
OK, when I said perfect I meant it is as expected. Haha.
I will get myself a tacho so I can provide figures and set the idle properly. |
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