Recently my truck has started to shut off at stop lights when sitting at idle. It looks like it's only idling around 500rpm. I can catch it sometimes by just tapping the accelerator.
I just got new plugs installed at the dealer (just because it's a pain to get at the back ones), but I can't imagine they'd mess with the idle. What's it supposed to be set at?
What's our idle supposed to be set to?
Moderator: F9K9
What's our idle supposed to be set to?
[size=75]2001 Onyx Black Crew Cab[/size]
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HenryJ
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Idle speed is controlled by the computer.
Listen for a vacuum leak and fix it if you find one.
You need to clean your throttle blade ,bore, and IAC valve (Idle Air Control).
Make sure they didn't crack your distributor housing - Plastic Distributor
If those are all good here's the GM diagnostic flow chart:
Sensor Checks
* Check the heated oxygen sensor (HO2S). Check for silicon contamination from fuel or from an improperly-used sealant. The sensor will have a white powdery coating. The sensor will produce a high but false signal voltage, or indicate a rich exhaust. The control module will reduce the amount of fuel delivered to the engine, causing a severe driveability problem.
* Check the throttle position (TP) sensor. If a sticking throttle shaft or binding linkage causes a high TP sensor open throttle indication, the control module will not control the idle. Monitor the TP sensor voltage. A scan tool or voltmeter should read less than 0.85 volts with the throttle closed.
* Check the engine coolant temperature (ECT) sensor using the scan tool in order to compare the engine coolant temperature with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5 degrees more than or less than the ambient air temperature on a cold engine, check for a high resistance in the coolant sensor circuit or the sensor itself.
* Check the manifold absolute pressure (MAP) sensor response and accuracy.
Fuel System Checks
* Check the fuel pressure. Refer to Fuel System Diagnosis .
* Check to determine if a rich or lean system causes the condition. Drive the vehicle at the speed of the complaint. Monitoring the fuel trim will help to identify the problem.
o Lean--The long term fuel trim is more than 150.
o Rich--The long term fuel trim is less than 115.
* Perform the fuel injector balance test. Refer to Fuel Injector Balance Test with Tech 2 .
* Check the fuel injector driver circuit.
1. Disconnect the injector harness connector at the injectors.
2. Connect an injector test lamp between the terminals of each injector connector and note the lamp while cranking.
3. If the test lamp fails to blink at any connector, the test lamp has a faulty injector drive circuit harness, connector, or terminal.
* Perform the fuel injector coil test. Refer to Fuel Injector Coil Test .
* Check the evaporative emission (EVAP) control system.
Ignition System Checks
* Check the ignition output using the J 26792 Spark Tester or the equivalent. Refer to Distributor Ignition (DI) System Diagnosis .
* Check for the following conditions:
o Wet plugs
o Cracks
o Wear
o Improper gap
o Burned electrodes
o Blistered insulators
o Heavy deposits
* Check the spark plug wires by connecting a DMM to the ends of each wire in question. If the meter reads over 30,000 ohms, then replace the wires.
Additional Checks
* Check for vacuum leaks. Vacuum leaks can cause a higher than normal idle and low idle air control (IAC) counts.
* Check the IAC operation. Refer to Idle Air Control (IAC) System Diagnosis .
* Check the control module grounds for being clean, tight, and in their proper locations.
* Check the scan tool to determine if the control module is receiving an A/C signal. If a problem exists with the A/C ON, check the A/C system operation.
* Check for the exhaust gas recirculation (EGR) being ON while idling which will cause roughness, stalling, and hard starting.
* Check the battery cables and ground straps. The cables and straps should be clean and secure.
* Check the crankcase ventilation valve for proper operation by placing a finger over the inlet hole in the valve end several times. The valve should snap back. If the valve does not snap back, replace the valve.
Engine Mechanical Check
Check for the following conditions:
* Broken motor mounts
* Improper valve timing
* Low compression
* Bent pushrods
* Worn rocker arms
* Broken or weak valve springs
* Worn camshaft lobes
Listen for a vacuum leak and fix it if you find one.
You need to clean your throttle blade ,bore, and IAC valve (Idle Air Control).
Make sure they didn't crack your distributor housing - Plastic Distributor
If those are all good here's the GM diagnostic flow chart:
Sensor Checks
* Check the heated oxygen sensor (HO2S). Check for silicon contamination from fuel or from an improperly-used sealant. The sensor will have a white powdery coating. The sensor will produce a high but false signal voltage, or indicate a rich exhaust. The control module will reduce the amount of fuel delivered to the engine, causing a severe driveability problem.
* Check the throttle position (TP) sensor. If a sticking throttle shaft or binding linkage causes a high TP sensor open throttle indication, the control module will not control the idle. Monitor the TP sensor voltage. A scan tool or voltmeter should read less than 0.85 volts with the throttle closed.
* Check the engine coolant temperature (ECT) sensor using the scan tool in order to compare the engine coolant temperature with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5 degrees more than or less than the ambient air temperature on a cold engine, check for a high resistance in the coolant sensor circuit or the sensor itself.
* Check the manifold absolute pressure (MAP) sensor response and accuracy.
Fuel System Checks
* Check the fuel pressure. Refer to Fuel System Diagnosis .
* Check to determine if a rich or lean system causes the condition. Drive the vehicle at the speed of the complaint. Monitoring the fuel trim will help to identify the problem.
o Lean--The long term fuel trim is more than 150.
o Rich--The long term fuel trim is less than 115.
* Perform the fuel injector balance test. Refer to Fuel Injector Balance Test with Tech 2 .
* Check the fuel injector driver circuit.
1. Disconnect the injector harness connector at the injectors.
2. Connect an injector test lamp between the terminals of each injector connector and note the lamp while cranking.
3. If the test lamp fails to blink at any connector, the test lamp has a faulty injector drive circuit harness, connector, or terminal.
* Perform the fuel injector coil test. Refer to Fuel Injector Coil Test .
* Check the evaporative emission (EVAP) control system.
Ignition System Checks
* Check the ignition output using the J 26792 Spark Tester or the equivalent. Refer to Distributor Ignition (DI) System Diagnosis .
* Check for the following conditions:
o Wet plugs
o Cracks
o Wear
o Improper gap
o Burned electrodes
o Blistered insulators
o Heavy deposits
* Check the spark plug wires by connecting a DMM to the ends of each wire in question. If the meter reads over 30,000 ohms, then replace the wires.
Additional Checks
* Check for vacuum leaks. Vacuum leaks can cause a higher than normal idle and low idle air control (IAC) counts.
* Check the IAC operation. Refer to Idle Air Control (IAC) System Diagnosis .
* Check the control module grounds for being clean, tight, and in their proper locations.
* Check the scan tool to determine if the control module is receiving an A/C signal. If a problem exists with the A/C ON, check the A/C system operation.
* Check for the exhaust gas recirculation (EGR) being ON while idling which will cause roughness, stalling, and hard starting.
* Check the battery cables and ground straps. The cables and straps should be clean and secure.
* Check the crankcase ventilation valve for proper operation by placing a finger over the inlet hole in the valve end several times. The valve should snap back. If the valve does not snap back, replace the valve.
Engine Mechanical Check
Check for the following conditions:
* Broken motor mounts
* Improper valve timing
* Low compression
* Bent pushrods
* Worn rocker arms
* Broken or weak valve springs
* Worn camshaft lobes
"Speed doesn't kill, suddenly becoming stationary does." - Richard Hammond
"Speed is just a matter of Money - How fast do YOU want to go?"-Mechanic from Mad Max-
If at first you don't succeed - Don't take up Skydiving! - ThunderII KE7CSK
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