TheSamba.com :: View topic - Troubleshooting Idle Control Valve (high idle)

Fri Jan 25, 2013 9:27 pm

I have this high idle issue that I'm having a hard time isolating.

I've gone thru the usual suspects:
Replaced the Temp II.
Checked ALL vacum lines.
Isolated the system from the charcoal canister.
Cleaned EVERY ground in the van front and back.
Checked the brake booster line and power steering switch.
Adjusted my TPS with a voltmeter.
Adjusted timing via Tencentlife method.
Made sure the contacts were snug and clean at the ISCU.
And I sprayed the ICV until it sparkled and "snapped" smartly when hooked up to a battery.

If I disconnect the ICV it idles very nicely at 800 rpm.. but when its connected it idles at 2000 rpm so I'm confident this is my source. I can squeeze shut the line and the idle drops back to 800 again so I think the ISCU is sending an erroneous signal to the ICV to stay open.. but I don't know why.

What info is the ISCU using to make this call?
I know they're prone to fail but do they typicaly fail like this?
Any tests I can perform?

Thanks!

Sat Jan 26, 2013 8:31 am

Reference page 10 in the digifant protraining manual.

Good schematic there with all the possible inputs to the unit that controls that valve.

Sat Jan 26, 2013 9:19 am

Your idle control unit is bad. This unit has a "push pull" transistor setup, that causes the buzzing. One pushes and one pulls the valve harder
or easier making the idle raise or fall. When one transistor goes bad it holds the valve open two one side, and the idle goes up. Unfortunately
lots if of "professional" mechanics think this is how is is suppose to
work and start screwing with a ton of other setting, and just make things worst!....
Eric

Mathew Zelezen wrote: I have this high idle issue that I'm having a hard time isolating.

I've gone thru the usual suspects:
Replaced the Temp II.
Checked ALL vacum lines.
Isolated the system from the charcoal canister.
Cleaned EVERY ground in the van front and back.
Checked the brake booster line and power steering switch.
Adjusted my TPS with a voltmeter.
Adjusted timing via Tencentlife method.
Made sure the contacts were snug and clean at the ISCU.
And I sprayed the ICV until it sparkled and "snapped" smartly when hooked up to a battery.

If I disconnect the ICV it idles very nicely at 800 rpm.. but when its connected it idles at 2000 rpm so I'm confident this is my source. I can squeeze shut the line and the idle drops back to 800 again so I think the ISCU is sending an erroneous signal to the ICV to stay open.. but I don't know why.

What info is the ISCU using to make this call?
I know they're prone to fail but do they typicaly fail like this?
Any tests I can perform?

Thanks!

Sat Jan 26, 2013 11:26 am

1vw4x4 wrote: Your idle control unit is bad.
I sort of recall Van-Cafe.com has "rebuilt" (refurbished) units and may require an exchange.

If you look, there maybe some thing out on the web for fixing them too.

Fun, eh?

Sat Jan 26, 2013 11:39 am

1vw4x4 wrote: Your idle control unit is bad. This unit has a "push pull" transistor setup, that causes the buzzing. One pushes and one pulls the valve harder
or easier making the idle raise or fall. When one transistor goes bad it holds the valve open two one side, and the idle goes up. Unfortunately
lots if of "professional" mechanics think this is how is is suppose to
work and start screwing with a ton of other setting, and just make things worst!....
Eric

Sorry to disagree. The valve is held shut by a spring. The ICU supplies a pulse width modulated voltage to the ICV. When the voltage is high, the coil of the ICV is energized and try to pull the valve open. But the duration of this voltage is short, before the valve is fully opened, the voltage is removed and the valve will move back to its original position - closed. But before it is fully closed, the next voltage came and try to open the valve again. So by varying the width ( duration ) of the "on" voltage and the " off " voltage, the valve can be controlled to open at any desired width. Because the valve is constantly opening and closing, you will feel the vibration on the valve body.
The measurement I've got is at idle, the on time for the ISV coil is 2.2 millisecond ( 1 mS = 1/1000 second ) and the off time is 4.1mS. When the power steering switch is closed, the on time is 2.6 mS and the off time is 3.8 mS. This is to increase the idle speed when the load on the engine is increased at idle.

Sat Jan 26, 2013 2:29 pm

Mathew Zelezen wrote: I have this high idle issue that I'm having a hard time isolating.

I've gone thru the usual suspects:

Checked the brake booster line and power steering switch.

Thanks!

How/where did you check these two items?

Thank you.

Sat Jan 26, 2013 2:35 pm

East test of the module. Open up the engine compartment, leave the lift gate up. Turn the ignition 'on' but do not start the engine. Walk back to the engine bay and listen for the ICV to buzz, and put your hand on it - it will be vibrating if the module is operating correctly. If it is not - the module behind the passenger tail light is bad. This happend to me - idle shot up to 2000+ until I replaced the module.

Sat Jan 26, 2013 7:45 pm

I also have been wondering about a high idle that seemed to develop over the last 6 months , so this thread caught my attention.

As I considered the possibility that the ICU is good but getting bad signals, I came across on page 24.54 Bentley the diagram showing rpm signal input connector to the ICU (left side engine compartment for our '86).

I refreshed this connection today, and the idle is now much better. Preliminary results to be sure, as I need to test this some more, and read up in the ProTraining, it shows all the ICU inputs, and rule out other possibilities.

Would a resistive connection here cause the ICU to increase idle? Dunno, but thought I'd throw it out there.

Sat Jan 26, 2013 8:37 pm

So will the ICV valve always vibrate when powered up in the vehicle? It clicks on and off on the bench . But does not vibrate when the key is on with the vehicle not running .
I have been fighting this for a while . I found a few problems today . A bad temp II sensor and an almost broken Distributor supply wire at the connector .
I was blaming the high idle to the bad Temp II sensor ,but it sounds like it could be the ICV . When running if I unplug it the idle drops from 1800 to about 950 and stays until I hit the throttle again . I am going to dig through my stuff ,I am sure I have another ICV and replace it .
I know my idle control relay is good ,it is a rebuilt unit from VC .

Stacy .

Sat Jan 26, 2013 9:13 pm

You've done a lot of checking but you didn't mention the the two basic checks. 1) Does the valve buzz when the key is switched ON ?
2) What is the milliamp current going thru the valve at hot idle speed ? The spec is in the bentley, I think it's 1032 mA.
Also I think it's possible to swap the wires to the ICV. If so the system would work in reverse !!! When rhe idle stab CU wanted to slow the idle speed, the ICV would open.......

John

Sat Jan 26, 2013 9:34 pm

The specified value is 430 mA and slowly fluctuating.

Sounds like the OP's valve is slamming wide open and staying there.....

Refer to pages 30-33 in the digifant Protraining Manual for a detailed, specific troubleshooting of the Idle stabilization system.

The valve doesn't vibrate continuously on post 1987 Vans, the wiring to it is different.......

Sat Jan 26, 2013 10:12 pm

Quote:
The valve doesn't vibrate continuously on post 1987 Vans, the wiring to it is different.......

I don't think so. The connection is the same.

Sat Jan 26, 2013 10:45 pm

Vwcrewman wrote: So will the ICV valve always vibrate when powered up in the vehicle? It clicks on and off on the bench . But does not vibrate when the key is on with the vehicle not running .
I have been fighting this for a while . I found a few problems today . A bad temp II sensor and an almost broken Distributor supply wire at the connector .
I was blaming the high idle to the bad Temp II sensor ,but it sounds like it could be the ICV . When running if I unplug it the idle drops from 1800 to about 950 and stays until I hit the throttle again . I am going to dig through my stuff ,I am sure I have another ICV and replace it .
I know my idle control relay is good ,it is a rebuilt unit from VC .

Stacy .
I believe in 88+ vans the ICV only vibrates when the fuel pump is running - so for a few seconds when key goes on initially, or when the engine is running.

Obviously it's much easier to determine if it's vibrating when the engine isn't running, so I recommend you get someone to pop the ignition on while you see if the ICV is buzzing during FP priming.

(the Bentley is in error on this, I believe)

Sat Jan 26, 2013 11:33 pm

I am curious what the year would have to do with it . Only because ,I do not know what year my harness is . Mine is an 89 that had a Digijet 112 HP harness in it . It has had different ECU and Idle control relays in it . There are different versions of the ECU and mine is a "D" and my Relay is a "D" as well . So my guess is that it would follow the ECU and relay and not the model year .
This is a "WAG" and I am going to swap it out tomorrow . It is also sluggish on accelerating and you can feel it when it gets up to temp ,it just flattens out .

Sat Jan 26, 2013 11:41 pm

Vwcrewman wrote: I am curious what the year would have to do with it . Only because ,I do not know what year my harness is . Mine is an 89 that had a Digijet 112 HP harness in it . It has had different ECU and Idle control relays in it . There are different versions of the ECU and mine is a "D" and my Relay is a "D" as well . So my guess is that it would follow the ECU and relay and not the model year .
This is a "WAG" and I am going to swap it out tomorrow . It is also sluggish on accelerating and you can feel it when it gets up to temp ,it just flattens out .
In either situation, the ICV should buzz/vibrate when the FP is priming - so get a friend to help out regardless. :)

Sun Jan 27, 2013 1:00 am

Thanks for the input all.

Since I have an 86 I'll make sure the valve is buzzing with the key on, and if it is use the Pro Training Manual to see what the ISCU is being told and what mA's its sending..

Those rebuilt units from VC are 189 bucks.. bleh. Maybe I'll take up electrical repair.

I'll let you know what I find.

Sun Jan 27, 2013 9:35 am

Thank you ,that answers my question .

Sun Jan 27, 2013 10:15 am

jptech wrote: You've done a lot of checking but you didn't mention the the two basic checks.
1) Does the valve buzz when the key is switched ON ?
2) What is the milliamp current going thru the valve at hot idle speed ?

3. Does the idle control KNOW that it should be controlling idle? Is the throttle position switch switching correctly?

That was the total cause of our very high idle speed (~1600rpm hot). With the switch adjusted, the idle's ~800ish.

Sun Jan 27, 2013 11:40 am

I fixed my idle problem! Thank you Samba! Here was the deal with my '86 Westy: My TPS was out of adjustment, and once I got that set correctly my idle problem returned after a only few weeks, dang. I checked the ICV and it vibrated when I turned the key on, and also when the engine was running, so I thought this was not the problem. Wrong! I unplugged it and idle came down to 900 and stayed there, prefect. I cleaned it out with carb cleaner like others have done, plugged it back in, and it worked! Idle is now perfect and steady. The lesson learned is that if your ICV vibrates it still may not be operating correctly. It may need a good cleaning. This actually makes sense because the mechanical parts of the valve get dirty and it is either not opening all the way or closing all the way or even both. Clean your ICV! It could save you a lot of money.

Sun Jan 27, 2013 1:44 pm

Mathew Zelezen wrote: Thanks for the input all.

Since I have an 86 I'll make sure the valve is buzzing with the key on, and if it is use the Pro Training Manual to see what the ISCU is being told and what mA's its sending..

Those rebuilt units from VC are 189 bucks.. bleh. Maybe I'll take up electrical repair.

I'll let you know what I find.

Check with Ben - he may have a module or two for sale in the classifieds. Not rebuilt - used - but he guarantees them to be in operable condition, and less cost than the rebuilts.