ISV command/control question - valve being commanded fully closed at idle
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ISV command/control question - valve being commanded fully closed at idle
Working on an '85 US auto.
First symptom was a giant sucking sound when warm - the hose from the ISV to the top of the manifold is being sucked flat at idle, as if there is no airflow through the ISV. Car will idle with idle screw turned fairly far open and runs strong off-idle.
Capped the idle stabilizer in/out hoses and with the ISV free to see, can see that when the car is idling the ISV is fully closed and is being told to do so - unit is pulsing itself fully closed. So, there's the problem. ISV is brand-new - old one was hanging up (verified on bench).
I've confirmed that the idle switch is contacting at both LH and EZF, WOT switch not active at idle, confirmed wiring to ISV with no cross-short or short-to-ground. Jumping the test connector at the front of the motor does not change the ISV response - stays fully closed.
Anyone know if this is a possible failure mode of the LH or if there's something else I'm missing?
Thanks very much - really stumped here.
First symptom was a giant sucking sound when warm - the hose from the ISV to the top of the manifold is being sucked flat at idle, as if there is no airflow through the ISV. Car will idle with idle screw turned fairly far open and runs strong off-idle.
Capped the idle stabilizer in/out hoses and with the ISV free to see, can see that when the car is idling the ISV is fully closed and is being told to do so - unit is pulsing itself fully closed. So, there's the problem. ISV is brand-new - old one was hanging up (verified on bench).
I've confirmed that the idle switch is contacting at both LH and EZF, WOT switch not active at idle, confirmed wiring to ISV with no cross-short or short-to-ground. Jumping the test connector at the front of the motor does not change the ISV response - stays fully closed.
Anyone know if this is a possible failure mode of the LH or if there's something else I'm missing?
Thanks very much - really stumped here.
Last edited by Incendier; May 7, 2009 at 09:05 AM.
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From: Not that far from the Jersey Shore
I suggest you test the new ISV to make sure it's capable of operating correctly.
The '85/'86 ISV has a 3 pin connector. The middle pin is the ground and the outer pins receive a signal from the LH to open and close the ISV. Get a hold of the wiring diagram and check the 3 pin connector to ground and back to the LH connector under the dash for continuity.
The '85/'86 ISV has a 3 pin connector. The middle pin is the ground and the outer pins receive a signal from the LH to open and close the ISV. Get a hold of the wiring diagram and check the 3 pin connector to ground and back to the LH connector under the dash for continuity.
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On the ISV/IAC/ICV connector, the center terminal is 12V+, the outer two are grounds to open or close. (LH/EZF pinouts)
The 12V+ is shared by the injectors, O2 sensor heater, and fuel pump, through the fuel pump relay, so normally, the engine has to be running to have power at the center terminal.
The 12V+ is shared by the injectors, O2 sensor heater, and fuel pump, through the fuel pump relay, so normally, the engine has to be running to have power at the center terminal.
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From: Davidsonville, MD
I would reinstall the ISV and then attach the jumper to the diagnostic plug to see if there is any change whatsoever in the idle speed. If there's no change, I'd put my money on a defective LH. Just curious, where are you located?
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Thanks, all.
Adam - have previously confirmed new ISV operation. Opens and closes correctly with voltage applied; compared to another currently operating unit I sourced today; operation is the same.
Ken and Adam - I was with Adam on this one; the car shows continuity to ground from the center connector, voltage at end pin when running. Either this is the only time in my life I'm going to disagree with Ken or we may be onto my problem.
Wally - Independent tach shows me approx. 550 rpm with the ISV lines plugged and the bypass screw opened slightly. Though I will take the polite inference of your comment and check again for vacuum leaks that may be driving my idle.
Further info, if it helps: only happens warm. ISV is open and functioning during cold starts. If I get on the gas at all, ISV opens proportionally with RPM up to about 4K. ISV opens slightly with A/C request, opens partially when I disconnect Temp II. Temp II wiring and resistance check out.
'Preciate you letting me pick your brains.
Adam - have previously confirmed new ISV operation. Opens and closes correctly with voltage applied; compared to another currently operating unit I sourced today; operation is the same.
Ken and Adam - I was with Adam on this one; the car shows continuity to ground from the center connector, voltage at end pin when running. Either this is the only time in my life I'm going to disagree with Ken or we may be onto my problem.
Wally - Independent tach shows me approx. 550 rpm with the ISV lines plugged and the bypass screw opened slightly. Though I will take the polite inference of your comment and check again for vacuum leaks that may be driving my idle.
Further info, if it helps: only happens warm. ISV is open and functioning during cold starts. If I get on the gas at all, ISV opens proportionally with RPM up to about 4K. ISV opens slightly with A/C request, opens partially when I disconnect Temp II. Temp II wiring and resistance check out.
'Preciate you letting me pick your brains.
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JHowell - we overlapped posting. Thank you. That is as I feared; I spoke with a PCNA rep who is a longtime tech who said the same.
I'm in Minnesota. I'll try to source an LH locally; could be tough.
I'm in Minnesota. I'll try to source an LH locally; could be tough.
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From: Not that far from the Jersey Shore
I stand corrected - Ken is right that the middle pin is 12V+.
I use a Power Probe to test small motors and should clearly label the test leads.
Sorry for the confusion.
I use a Power Probe to test small motors and should clearly label the test leads.
Sorry for the confusion.
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Many of the inputs and outputs of the LH/EZK have voltage on them until they are used for grounding.
For example, the WOT and idle inputs measure +5V until the throttle switch grounds them. (Large resistors limit the amount of current.)
Note: I only barely understand this e-lec-tronical stuff.
For example, the WOT and idle inputs measure +5V until the throttle switch grounds them. (Large resistors limit the amount of current.)
Note: I only barely understand this e-lec-tronical stuff.
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I've got a spare set of LH/EZF. You're welcome to borrow them for a few weeks for the cost of shipping both ways. I just need it back in time for SITM (dyno day the following week and I have some tests I'll need them for.
PM with address if you need it.
PM with address if you need it.
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Nice!
Thank you all...it'll be a day before I can get back to 'er.
I have sourced a good LH locally for testing - charitable owner - and will be trying it shortly after I review everything *I* could have done.
Will report back.
Thank you all...it'll be a day before I can get back to 'er.
I have sourced a good LH locally for testing - charitable owner - and will be trying it shortly after I review everything *I* could have done.
Will report back.
