3,2 -1986 Idle problems
05-05-2011, 03:02 PM
#1
Track Day
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3,2 -1986 Idle problems
Hi guys.
Have a problem with idle that will not stabilize at all. It goes from around 1000 rpm and up to 2000 rpm and down again and continues like a robot. Not sure I explaine it right but it does it with a exactly pattern without a mistake. The ICV is new and checked the wires from DME. Checked idle switch (microswitch), vacuumleaks. Have not checked the CO at idle , checking that tomorrow.
If you blocking the hose that goes to ICV the engine stabilize around 800 rpm and stays there so can`t really understand that.
Car is a 3,2 1986 without catalyst.
Any suggestions ? Thanks
Have a problem with idle that will not stabilize at all. It goes from around 1000 rpm and up to 2000 rpm and down again and continues like a robot. Not sure I explaine it right but it does it with a exactly pattern without a mistake. The ICV is new and checked the wires from DME. Checked idle switch (microswitch), vacuumleaks. Have not checked the CO at idle , checking that tomorrow.
If you blocking the hose that goes to ICV the engine stabilize around 800 rpm and stays there so can`t really understand that.
Car is a 3,2 1986 without catalyst.
Any suggestions ? Thanks
05-05-2011, 09:44 PM
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I had the same issues last year and ultimately it was a vacuum leak. If it is a leak it can take a lot of patience to find it. There are a bunch of other threads you can search for this same problem that may offer some other suggestions.
05-05-2011, 11:53 PM
#3
I haddah Google dat
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The most likely cause is a vacuum leak, which causes the mixture to be too lean (false air). I would not do something like unplug the O2 sensor. You can adjust the CO% as others have, but I feel that is simply a band aid, and the problem may re-appear later. To me, it makes sense to check ALL vacuum leak sources first, check the operation of the ICV servo after the engine is hot (remove it, then plug in the harness, and observe the valve opening half way with the engine off), and then re-set idle speed, and last mess with CO% with an afr gauge attached.
05-06-2011, 12:55 AM
#4
"If you blocking the hose that goes to ICV the engine stabilize around 800 rpm and stays there so can`t really understand that."
That's key to understanding the problem!
Most likely the DME ECM idle valve circuitry was damaged by the valve
having shorted windings. A simple test is to disconnect the valve and remove
it. Then rotate the vane inside so the valve is fully closed and replace the
the valve without connecting the electrical connector.
Start the engine and monitor the RPM which should be around 600 - 700.
If it's not, then you have a large air leak around the throttle body. Next,
connect the electrical connector and if the idle surges above a 1000,
then the DME ECM has a bad idle circuitry. It's also possible that the
valve is sticking open or the wiring to the DME ECM is bad.
Other Comments:
"The most likely cause is a vacuum leak, which causes the mixture to be too lean (false air)."
Not really. A lean mixture which bypasses the throttle body & AFM will cause
the engine to have a rough/poor/low idle. When the air leak bypasses the
throttle body but not the AFM (this situation), the engine will surge because
the mixture is proper as the air flows thru the AFM and NOT around it.
Thus causing the engine to rev until the DME ECM shuts the injectors off
and subsequently until the RPM drops below the shutoff point causing it
to rev again.
That's key to understanding the problem!
Most likely the DME ECM idle valve circuitry was damaged by the valve
having shorted windings. A simple test is to disconnect the valve and remove
it. Then rotate the vane inside so the valve is fully closed and replace the
the valve without connecting the electrical connector.
Start the engine and monitor the RPM which should be around 600 - 700.
If it's not, then you have a large air leak around the throttle body. Next,
connect the electrical connector and if the idle surges above a 1000,
then the DME ECM has a bad idle circuitry. It's also possible that the
valve is sticking open or the wiring to the DME ECM is bad.
Other Comments:
"The most likely cause is a vacuum leak, which causes the mixture to be too lean (false air)."
Not really. A lean mixture which bypasses the throttle body & AFM will cause
the engine to have a rough/poor/low idle. When the air leak bypasses the
throttle body but not the AFM (this situation), the engine will surge because
the mixture is proper as the air flows thru the AFM and NOT around it.
Thus causing the engine to rev until the DME ECM shuts the injectors off
and subsequently until the RPM drops below the shutoff point causing it
to rev again.
