1995 Base Idle Setting
11-15-2011, 05:14 PM
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1995 Base Idle Setting
Every search on how to do this yields non LT1 results. Given my car has mods and previous owner bored throrttle body and messed with throttle plate stop screw I need to put it back right. I have it running fine now but with my IAC counts at 0 I know I am not set right and idle is probably a bit too high.
Of course the FSM does not mention as they never intended that screw to be monkeyed with.
I have a new IAC on the way and want to put it all back together correctly. I know the procedure for resetting the IAC and that the TPS is not adjustable, but the plate stop screw not sure on. Or is it simply at this point since it is not stock adjusting that screw until I get a RPM I like.
Any directions or link out there? Do these insturctions still apply to a 1995, found them in an early LT1 car thread
Turn on the ignition, but DON'T start the engine. This will force the ECM into its diagnostic mode. Wait 30 seconds to allow the IAC pintle to fully extend. With the ignition still on, go under the hood, remove the electrical connector from the IAC, then turn off the ignition and remove the paper clip jumper from the ALDL. With the IAC pintle fully extended (closed) all idle air will be controlled by the position of the throttle plates. Some manuals indicate that the EST bypass connector should be disconnected for this procedure, while some make no mention of it. While timing is a factor in idle speed, the EST should only operate as a function of engine RPM, temperature, and detonation sensor inputs. To remove all doubt, disconnect the EST bypass connector is your car is so equipped. Some TBI and V-6 engines do not have this bypass connector, and therefore must be set with no regard to the EST system. The EST can be bypassed on some cars by grounding the diagnostic terminal at the ALDL and continuing with the procedure, but the fuel mixture will be skewed to the rich side, affecting idle speed as well. In any event, the minimum air position idle speed range is wide enough to allow for some variations. As always, it is best to consult your service manual for the exact procedure for your system.
Locate the Torx screw on the left side of the throttle body. It may be equipped with a protective metal cap from the factory. This was intended to discourage adjustment. If the cap is present, use a small punch to knock it out. Once the screw is accessible, start the engine and place the transmission in DRIVE. Adjust the throttle stop to obtain 400-450 RPM with the transmission in "DRIVE" on an automatic transmission car, 450-550 in neutral on a manual transmission car, rotating the Torx screw clockwise to raise speed and counter-clockwise to lower speed. Once the idle RPM is set, place the transmission in PARK and turn off the engine.
Re-connect the electrical connector onto the IAC. Start engine. Idle speed should be governed by the ECM at approximately 600-650 rpm in "DRIVE" (for unmodified cars). Idle speed in NEUTRAL or PARK is less significant, and will be higher.
And then just use the IAC reset method as normal for 1995?
Of course the FSM does not mention as they never intended that screw to be monkeyed with.
I have a new IAC on the way and want to put it all back together correctly. I know the procedure for resetting the IAC and that the TPS is not adjustable, but the plate stop screw not sure on. Or is it simply at this point since it is not stock adjusting that screw until I get a RPM I like.
Any directions or link out there? Do these insturctions still apply to a 1995, found them in an early LT1 car thread
Turn on the ignition, but DON'T start the engine. This will force the ECM into its diagnostic mode. Wait 30 seconds to allow the IAC pintle to fully extend. With the ignition still on, go under the hood, remove the electrical connector from the IAC, then turn off the ignition and remove the paper clip jumper from the ALDL. With the IAC pintle fully extended (closed) all idle air will be controlled by the position of the throttle plates. Some manuals indicate that the EST bypass connector should be disconnected for this procedure, while some make no mention of it. While timing is a factor in idle speed, the EST should only operate as a function of engine RPM, temperature, and detonation sensor inputs. To remove all doubt, disconnect the EST bypass connector is your car is so equipped. Some TBI and V-6 engines do not have this bypass connector, and therefore must be set with no regard to the EST system. The EST can be bypassed on some cars by grounding the diagnostic terminal at the ALDL and continuing with the procedure, but the fuel mixture will be skewed to the rich side, affecting idle speed as well. In any event, the minimum air position idle speed range is wide enough to allow for some variations. As always, it is best to consult your service manual for the exact procedure for your system.
Locate the Torx screw on the left side of the throttle body. It may be equipped with a protective metal cap from the factory. This was intended to discourage adjustment. If the cap is present, use a small punch to knock it out. Once the screw is accessible, start the engine and place the transmission in DRIVE. Adjust the throttle stop to obtain 400-450 RPM with the transmission in "DRIVE" on an automatic transmission car, 450-550 in neutral on a manual transmission car, rotating the Torx screw clockwise to raise speed and counter-clockwise to lower speed. Once the idle RPM is set, place the transmission in PARK and turn off the engine.
Re-connect the electrical connector onto the IAC. Start engine. Idle speed should be governed by the ECM at approximately 600-650 rpm in "DRIVE" (for unmodified cars). Idle speed in NEUTRAL or PARK is less significant, and will be higher.
And then just use the IAC reset method as normal for 1995?
Last edited by C4GUY; 11-15-2011 at 05:43 PM.
11-15-2011, 06:14 PM
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Or summarize like this?
1) Ground the diagnostic connector for 30 sec (which pins on 95, don't have a&b, the same ones I would use for pulling codes on the digital dash? - this will force IAC pintle all the way out, then disconnect IAC
2) Start engine, turn adjustment screw such that I am at the (625RPM in Neutral or 550RPm in drive (what my tune is set at). I have read mixed reports if it makes a difference if you do this in park, neutral or drive?
3) Shut off, plug IAC back in
4) Reset IAC using gas pedal method
1) Ground the diagnostic connector for 30 sec (which pins on 95, don't have a&b, the same ones I would use for pulling codes on the digital dash? - this will force IAC pintle all the way out, then disconnect IAC
2) Start engine, turn adjustment screw such that I am at the (625RPM in Neutral or 550RPm in drive (what my tune is set at). I have read mixed reports if it makes a difference if you do this in park, neutral or drive?
3) Shut off, plug IAC back in
4) Reset IAC using gas pedal method
Last edited by C4GUY; 11-15-2011 at 06:16 PM.
07-03-2014, 01:52 AM
#3
Melting Slicks
did you ever figure everything out? I'm assuming so since it's been years. I was doing a search for setting the lt1 idle and saw this thread. I also was having trouble finding info on the later cars (mines a 92).
05-20-2017, 04:46 AM
#4
Race Director
You shouldn't have to do a minimum idle adjustment on an LT1/LT4. The ECM notes the TPS voltage at startup and calls that "idle". It then uses that as a basis for running at other throttle openings.
