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My vanagon runs and idles smoothly in the morning, the problem…

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My vanagon runs and idles...
My vanagon runs and idles smoothly in the morning, the problem when the engine warmed up or after running for a while,it sometimes almost cut out at idle speed and the engine keeps idling up and down by itself.
Model 1986 Vanagon 2.1L manual.
Tune up done with new parts:
-new fuel pump and fuel filter,FP relays
-new alternator,terminal 30 connector replaced.
-ECU tested ok with another vanagon.
-MPG is 14.5 combined.
-Temperature is fine.
Is there a test on the Idle Stabilizer Control Module?
Submitted: 12 years ago.Category: VW
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Answered in 27 minutes by:
12/10/2009
VW Mechanic: Jeremiah Mahler, ASE Certified Technician replied 12 years ago
Jeremiah Mahler
Jeremiah Mahler, ASE Certified Technician
Category: VW
Satisfied Customers: 200
Experience: ASE Master Certified with advanced L1, California Smog Tech, Volkswagen Certified
Verified
The idle going up and down could be related to the idle stabilizer module. In some cases it may also cause a crank no start. A good way to see if it is the problem is to bypass it. The two connectors in to the module can be disconnected and then connected to each other (which will bypass the module).

The poor running problems when warm could be caused by a O2 sensor that is faulty or producing false readings. The O2 sensor could produce false readings if there are exhaust leaks. The exhaust can be visually inspected for leaks and by listening for noise while the engine is running. The O2 sensor can be tested (min range, max range, response time, etc) but this is best done by a shop that knows Vanagons and has a 5 gas analyzer.
Jeremiah Mahler
Jeremiah Mahler, ASE Certified Technician
Category: VW
Satisfied Customers: 200
Experience: ASE Master Certified with advanced L1, California Smog Tech, Volkswagen Certified
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Customer reply replied 12 years ago

The mileage is currenlty 150K miles and I replaced the O2 sensor right before it reached 100K miles, I should replace the Idle Stabilizer module next.

 

For now should I increase the idle speed to higher RPM? How to?

The hot idle speed is currently 800RPM.

 

Thank you.

VW Mechanic: Jeremiah Mahler, ASE Certified Technician replied 12 years ago
The idle speed is not normally adjusted and therefore there is no provision for doing so.

Another thing to check is the throttle switches. There is one switch the changes for idle to off idle and another at wide open throttle. With the engine off if you listen closely while moving the throttle you should hear a slight "click" when moved. If not you could have a defective switch.
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Customer reply replied 12 years ago
The vanagon is now idle smoothly at 900+-RPM. Thank you.IdleSpeedAdjustments
VW Mechanic: Jeremiah Mahler, ASE Certified Technician replied 12 years ago
nice work! Smile
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Customer reply replied 12 years ago
The problem of idle going up and down now resurfacing again. That means I adjusted idle speed to higher +900RPM still did not fix the problem.
VW Mechanic: Jeremiah Mahler, ASE Certified Technician replied 12 years ago
I would check the items as I described in previous posts (bypass idle stabilizer, check throttle switches).
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Customer reply replied 12 years ago
I am trying to get a hold of the Service Training manual below, so I can be more confident testing the Stabilizer module.
Hope I can find there is a procedure with details step by step.
Service Training
VW Mechanic: Jeremiah Mahler, ASE Certified Technician replied 12 years ago
The easiest way to test the idle stabilizer is to bypass it.
And this is easily done by unplugging its connectors and connecting them to each other. If the problem goes away it is probably a faulty idle stabilizer.
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Customer reply replied 12 years ago
I see there are 2 locations for the Idle Stabilization System:
-Idle Stabilizer Control unit
-Idle Stabilization bypass valve

Idle Stabilization systemIdle bypass valve
The Idle Stabilization System maintains the idle speed by
adjusting the volume air entering the engine at idle.

I will also clean the Idle stabilizer valve and its hoses
ducts to ensure proper mechanical operation of the idle bypass valve.
VW Mechanic: Jeremiah Mahler, ASE Certified Technician replied 12 years ago
The idle speed control unit changes idle speed by changing the ignition timing. It is the one that can be bypassed.

I would suspect the idle speed valve if the idle speed sporadically changes/drops or does not idle. Cleaning it can't hurt. Sometimes they get gummed up over the years.
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Customer reply replied 12 years ago
After I inspected the idle valve last week, the engine idled smoothly for about 5 days. Today when I sudden stop the van at a stoplight and then the engine began idle up/down again. The hard stop caused the symptom resurfaced again.
I tried to push that throttle arm (as pointing with red arrow), I felt the Throttle Shaft is sluggish and it seems to be the coil spring action is not smoothly released.
VW Mechanic: Jeremiah Mahler, ASE Certified Technician replied 12 years ago
So far you have adjusted the idle up and inspected the idle valve but the problem is still present.

Have you tried bypassing the idle stabilizer module?

Have you checked the throttle switches?
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Customer reply replied 12 years ago
I unplugged and inspected the Idle Stabilizer module as seen in the picture, it looks clean:
Idle control unit

I believe that the Throttle Switch is not clicking since VOM shows no continuity at idle:
Throttle switch continuity tests

This defective idle switch explained why the cold idle and hot idle are malfunctioning.

I don't know how often this Throttle Switch are being replaced, but it costs $93.00 new,
if this switch is easy to replace then I'll try to fix it.

Finally, a defective switch is found, cheers!

Thanks for your help.

Bryant.
VW Mechanic: Jeremiah Mahler, ASE Certified Technician replied 12 years ago
Your idle stabilizer module is a different style that cannot be easily bypassed. Not sure how to test it other than replacing with a known good unit.

There are 2 throttle switches. One signals idle and the other signals wide open throttle (WOT). Try to actuate the switch by moving the throttle or moving the switch manually to see if they work. If the switches work but they are not being actuated by the throttle correctly they may just need to be adjusted.
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Customer reply replied 12 years ago
HAPPY NEW YEAR!
I turned the throttle shaft to actuate the switch and seeing that there is only one signal
at WOT where I hear the VOM beeps continously, meaning continuity for WOT.

I connected a voltmeter to the switch at the point shown in the picture and the measured voltage is correctly at 5.0V.
Throttle Switch checks

The throttle switch has no idle signal, thus it is not working when closed throttle, but it is working when WOT.
Following your advice, I should do the manual switch adjustment along with Throttle valve overhauling.
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