About to throw the car off a cliff
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Tiger03447 (10-24-2023)
10-15-2023, 10:00 AM
#47
Burning Brakes
Thread Starter
I did notice something new, when I turn the AC on the rpm drops to 950 rpm.
not sure of normal or not.
Last edited by Last Lemming; 10-15-2023 at 12:09 PM.
10-17-2023, 11:48 AM
#48
Drifting
Either the ISV is not compensating (you're getting normal load drop) or it's working opposite like. Is it possible to wire it so it works in reverse? I've changed mine ages ago & forget the plug
10-17-2023, 09:49 PM
#49
Still waiting on test results.
10-18-2023, 08:47 PM
#50
Burning Brakes
Thread Starter
I disconnect the ISV plug and then connected a 12v power source and confirmed the unit is working - in both directions. I then set the unit to be closed and started the car - with it still unplugged. It held at about 500 rpm until it warmed up then it rose to factory settings at about 925 rpm solid!
I then reconnected the ISV and started the car and the rpm went to 1100 rpm immediately.
I’m surmising something is causing the ISV to stay open after it has warmed up.
what should I check next?
I also pulled the TB and checked the plate tolerances and it was tight and solid. No gaps or loose TB plate. Throttle cable is good too.
Thoughts?
10-19-2023, 09:25 AM
#53
Burning Brakes
Thread Starter
How does the ISV get it's signal to work?
Meaning, what sensors are involved on the car (temperature, O2, etc) that tells the DME whether to open or close the ISV?
The reason I ask is currently while my ISV is new and has been tested to verify it's working correctly, when the car starts the ISV is open and does not close once warmed up. Assuming there isn't a wiring problem (such as shorted wires or broken connections) what set of sensors would tell it to stay open? That will be my next line of investigation once I finish verifying the wiring is ok.
Meaning, what sensors are involved on the car (temperature, O2, etc) that tells the DME whether to open or close the ISV?
The reason I ask is currently while my ISV is new and has been tested to verify it's working correctly, when the car starts the ISV is open and does not close once warmed up. Assuming there isn't a wiring problem (such as shorted wires or broken connections) what set of sensors would tell it to stay open? That will be my next line of investigation once I finish verifying the wiring is ok.
10-19-2023, 12:21 PM
#56
Burning Brakes
Thread Starter
is does click and I have verified it’s is a functional unit
it’s got to be more than the TPS, right? Because once the car is warmed up and the throttle is closed, the ISV should also be closed because the engine warmed up. When the car is cold, the ISV should be open, even when the throttle closed at idle, and both cases the TPS is in the same position at the ISP is operating in two different ways , so I’m not sure how the TPS is the only thing involved to controlling this
10-19-2023, 12:24 PM
#57
Burning Brakes
Thread Starter
10-19-2023, 01:01 PM
#58
Burning Brakes
Join Date: Oct 2021
Location: Southern WI - 89S2 Megasquirt PNP
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is does click and I have verified it’s is a functional unit
it’s got to be more than the TPS, right? Because once the car is warmed up and the throttle is closed, the ISV should also be closed because the engine warmed up. When the car is cold, the ISV should be open, even when the throttle closed at idle, and both cases the TPS is in the same position at the ISP is operating in two different ways , so I’m not sure how the TPS is the only thing involved to controlling this
it’s got to be more than the TPS, right? Because once the car is warmed up and the throttle is closed, the ISV should also be closed because the engine warmed up. When the car is cold, the ISV should be open, even when the throttle closed at idle, and both cases the TPS is in the same position at the ISP is operating in two different ways , so I’m not sure how the TPS is the only thing involved to controlling this
From
https://rennlist.com/forums/924-931-...dle-speed.html
Start with the screw and locknut on the throttle linkage, that is not an adjustment, it's a setting. Loosen the locknut and back off the screw, turn in the screw until it just touches the linkage, turn it in an additional 1/4 turn, lock it down with the nut. At this point check that the idle switch clicks as soon as you open the throttle, and that when you release the throttle that it clicks again. If it does not then you will need to adjust the switch until it operates correctly, or replace it if it can't be made to work. The second screw on the throttle body is the idle speed adjustment screw, in an early car, simply turn it until the car runs at approx 800 rpm. In a second gen. 944 you first need to bypass the idle stabilizer by bridging the contacts in the test connector in the left rear corner of the engine compartment, then set speed to 800 rpm or set it so that it does not change when you plug and unplug the bridge. The allen on the air flow meter effects air fuel mixture, it has the greatest effect at idle, you can get it in the neighborhood by ear, but to do it right you need an emissions analyzer. Disconnect the o2 sensor and adjust the screw until the engine runs smoothest. If you u have an analyzer measure the exhaust ahead of the cat. converter and set mixture to about .8% CO. You might try pulling the boot off the throttle body and cleaning the area around the throttle plate. Use some carb cleaner and an old toothbrush to make it as clean as possible, clean the bore and the throttle plate itself. Over time deposits build up around the plate and restrict airflow to the engine, idle stabilizer values are set based on the supposition that the engine is getting a certain amount of air through the throttle body, if you cut that off then the engine will not be getting enough to run correctly, especially when it is cold and requires more airflow than when warm.
The idle adjustment is on the throttle body. Look for a slotted "screw." The only other adjustment on the throttle body is for the throttle plate mechanical stop. This is adjusted with a screw and lock nut.
To set the mechanical stop you need to remove the throttle body, loosen the screws for the throttle position switch, back out the mechanical stop, turn the stop screw until it just touches the stop arm, turn the stop screw in an additional 1/2 turn, and then tighten the lock nut.
To set the mechanical stop you need to remove the throttle body, loosen the screws for the throttle position switch, back out the mechanical stop, turn the stop screw until it just touches the stop arm, turn the stop screw in an additional 1/2 turn, and then tighten the lock nut.
On the early cars idle is "set" mechanically. The only "automatic" idle compensation is a solenoid valve (mounted at the rear of the air box) that opens when the A/C is running.
Last edited by walfreyydo; 10-19-2023 at 01:32 PM.