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ISCV no start?

2K views 1 reply 2 participants last post by  supraz 
#1 ·
My 85 L- Type had weird idle issues and eventually started to rev itself, then stalled out. It will not start now, could the ISCV cause a no start condition?
 
#2 ·
I suffered through hard starting issues that were ultimately caused by the ECU not stepping the ISCV. First, a really high idle speed can be caused by a manifold leak. The ECU controls the idle speed by setting the air flow into the motor. If there is a large leak, the idle speed will soar.
In my case, the ISCV was stuck so the motor ran at about 650rpm with the engine hot. When cold, the engine would idle low.
To see if your ISCV is stuck wide open, you can crimp the black hose that runs from the ISCV to the air intake on top of the manifold. This circuit bypasses the throttle blade.
If someone cranks your car while you partly crimp the tube shut will it start?
If the ISCV control is working properly, when you shut the key off you will actually hear a click-click-click sound as the ECU sets the ISCV wide open. The idea is that the next time you start the motor it has enough air to start and the ECU knows what position the ISCV is in (wide open). When you start, the ECU quickly steps the ISCV down to a position that causes the engine to idle at about 1250 rpm cold.

I found it interesting that while I was troubleshooting the ISCV that I could manually step the ISCV open and closed. When I had it wide open and tried to start the car the engine would rev to about 2,500 rpm then dip to 500 rpm and then cycle back and forth. I think the ECU was using the ignition timing to try to prevent the engine from running away.

Hope this helps.

Dale
 
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