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3D
Samba Member
Joined: October 19, 2007
Posts: 8
Location: San Francisco
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 Posted: Mon Dec 08, 2008 1:45 pm Post subject: Idle Control Valves? |
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| I need a new idle control valve for my 1987 Westie. Is there any chance this valve could be cleaned with a lubricant and reused so the valve wo't stick again and rev the engine? This is an expensive item... thanks |
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meyervw
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Joined: January 29, 2006
Posts: 470
Location: Chico, California
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| Posted: Mon Dec 08, 2008 2:22 pm Post subject: |
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I have successfully done this to one on a BMW. I used transmission fluid. poored in in and shook the hell out of it. Dump the fluid out and it is still working. I have the same problem as you and will try this out tomarrow with my Van. I will let you know if it works.
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Gustav 1987 Wolfsburg Edition |
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VanagOnly
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Joined: September 04, 2007
Posts: 81
Location: NYC,NY
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| Posted: Mon Dec 08, 2008 5:11 pm Post subject: |
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Try some carb cleaner ,then blow it out with compressed air.
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87 Wolfie
Past rides:72 Bus- RIP
72 Volvo 145 wagon-RIP
76 Jeep Wagoneer-RIP
67 Bug Dad's Daily-Project |
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24inchstance
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Joined: March 01, 2005
Posts: 133
Location: Santa Cruz, Ca
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| Posted: Mon Dec 08, 2008 5:17 pm Post subject: |
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I 2nd the carb cleaner. Ive used this method with success.
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1990 Westy MV
2.2L WBX w/ LSD
1986 Darth Moped
81 Centurion |
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tencentlife
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Joined: May 02, 2006
Posts: 10075
Location: Abiquiu, NM, USA
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| Posted: Mon Dec 08, 2008 7:24 pm Post subject: |
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Yes, liberal application of carb cleaner and a good blowout are often effective.
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240Gordy
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Joined: May 15, 2008
Posts: 2354
Location: Vancouver, BC
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| Posted: Wed Dec 10, 2008 4:35 pm Post subject: |
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I found my idle control unit on the left side of the engine comartment, next to the ECU, but where is the valve itself, I can't seem to find it?
The little unit costs $190.00 from Volkswagen. Van-Cafe is looking like a great deal.
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Tencentlife said,
"So, now that you know what you're doing, go to town."
2010 GOLF TRENDLINE 2.5
1985 GL now with more! a 2.1L
H&R SPORT(RED) Springs FRONT , SLAM SPECIALTIES RE6 AIRBAGS REAR |
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tencentlife
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Joined: May 02, 2006
Posts: 10075
Location: Abiquiu, NM, USA
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| Posted: Wed Dec 10, 2008 5:38 pm Post subject: |
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Your '85 doesn't have one.
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240Gordy
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Joined: May 15, 2008
Posts: 2354
Location: Vancouver, BC
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| Posted: Wed Dec 10, 2008 7:11 pm Post subject: |
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so how does it control the idle then?
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Tencentlife said,
"So, now that you know what you're doing, go to town."
2010 GOLF TRENDLINE 2.5
1985 GL now with more! a 2.1L
H&R SPORT(RED) Springs FRONT , SLAM SPECIALTIES RE6 AIRBAGS REAR |
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tencentlife
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Joined: May 02, 2006
Posts: 10075
Location: Abiquiu, NM, USA
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| Posted: Wed Dec 10, 2008 7:18 pm Post subject: |
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Search "DIS".
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240Gordy
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Joined: May 15, 2008
Posts: 2354
Location: Vancouver, BC
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| Posted: Thu Dec 11, 2008 3:34 pm Post subject: |
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doesn't work, the search only returns that post.
edit, never mind, I don't know how to search . . .
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Tencentlife said,
"So, now that you know what you're doing, go to town."
2010 GOLF TRENDLINE 2.5
1985 GL now with more! a 2.1L
H&R SPORT(RED) Springs FRONT , SLAM SPECIALTIES RE6 AIRBAGS REAR |
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floggingmolly
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Joined: April 06, 2007
Posts: 1106
Location: San Diego, CA
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| Posted: Thu Dec 11, 2008 4:21 pm Post subject: |
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| tencentlife wrote: |
No, sorry, there's no subtractive function in the Digijet ECU that "brings the idle down". But it could fluctuate idle if the TB switch is opening and closing, because then the ECU is going into and out of its idle injection mode. Or it could be getting an erratic signal from the Temp2 coolant sensor, so the ECU is in idle mode but it makes idle mixture rich, then lean, etc. Or the ignition could respond to fluctuating idle vacuum and cause the surging up and down. But the ignition and FI ECU are totally independent systems on Digijet, only sharing the rpm signal from the Hall gen in the diz via the Digital Idle Stabilizer.
The single item in nelinor's parts list that conceivably could have killed the motor is the Digital Idle Stabilizer box. The test to have done at the time would have been to simply unplug the two round connectors from the DIS and plug them together. If it was the DIS at fault, the engine would have started and run again, albeit with a possibly low or weak idle. You can bypass the DIS and run like that indefinitely if you like; everything downstream is blind to whether it is actually there or not.
The DIS is an additive device; it senses engine rpm because the Hall signal from the diz passes thru it. If it senses the engine is at idling speed but the speed dips too low, it phases the rpm signal waveform forward so the outgoing rpm signal is a little ahead of the base signal it is receiving from the diz, effectively advancing the idle timing a bit by making the ignition transistor control unit do what it's already doing, but a little bit earlier relative to the diz position. It varies the phasing dynamically to keep the engine idling within a programmed range, but it is only additive, meaning it can only advance and speed up, not retard and slow down the idle speed. That's why the base idle speed is set with the DIS bypassed, and it is lower than the ideal speed; the DIS can only add, not subtract, from idle speed. The ECU is, again, blind to what the DIS does to the rpm signal.
The Digijet ECU is pretty passive in all this. It's reading the rpm signal being passed on to it after the DIS, comparing it to the load and intake air temp signals from the AFM and engine temp signal from the Temp 2, and pulsing the injectors to give the appropriate amount of fuel. If the TB switch is properly closed at idle, the ECU is using it's idle quantity program, but it's incorporating those signals nonetheless and even if the TB switch is open, the ECU will still integrate those signals to determine the appropriate injector pulsewidth. The Digijet ECU gets no info about ignition, it only knows the present rpm.
The problem is that the rpm signal passes thru the DIS on its way to the ignition transistor control unit and on to the ECU. When the DIS starts to go, often the signal is degraded or interrupted by the DIS. This can make for wanky idle, eventually progressing to missed injection pulses and missed ignition events by both the ECU and ignition control module. Sometimes the signal can be interrupted completely, so the engine dies. In any of these instances, if you bypass the DIS and the engine runs normally again, that shows that the DIS is at fault. DIS's fail frequently by this age, so this isn't at all unusual. Luckily you can bypass and run without it with no problems, and new ones aren't very expensive.
So, for the surging idle, you should rule out vacuum leaks, but given the work you just did I would first pay attention to a few other things:
Make sure the Temp2 sensor is firmly seated in the water housing and it's connector is very clean and tight. Check continuity between the sensor body and chassis ground; there should be no measurable resistance.
Then make sure the TB switch is closed and staying closed at idle; try unplugging the two wires on either of the TB switches and patch them together. If it now idles smoothly without surging then the problem is that the switch isn't staying closed at idle. This can be due to wear in the throttle body shaft or just misadjustment of the switch itself.
The time delay after startup before the idle gets bad suggests trouble in the O2 sensor signal. This is very common when replacing the sensor because the signal wire gets manipulated which often shows up unseen damage in the signal coax wire where the signal-carrying center core gets shorted to ground. If it starts OK, runs fine for a short time after startup (from up to 10 minutes when cold to only about one minute when the engine is already warm), but then runs very rich, this could be the problem. Confirmation of it is when you restart the engine, it goes back to running fine, and gets bad aain after the same short time delay. If this is the case, the easy test is to let it idle when it is running badly, with everything connected as normal, and put a jumper between the o2 sensor connector and ground. If the idle degrades when you ground the signal wire, then you do not have a shorting problem there. If there is a change in idle to rich when you ground the connector, you want to test further: disconnect both the o2 sensor and the ECU, and test for continuity between the sensor signal connector at the free end of the green coax cable and ground. Wiggle the cable and make sure the signal core never shorts to ground.
I would rule out these things because the work you did could have induced problems in any of them. If all these things check out, then spend some time hunting down vacuum leaks. |
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