Erratic idle when first started
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Safety Car
Joined: Aug 2000
Posts: 3,507
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From: Easton CA
Erratic idle when first started
The last few weeks I have noticed that occasionally, when I first start my '92, it idles at about 300 RPMs. I was surprised it would idle so slow. After it warms up everything seems to straighten itself out. Any ideas? Most other times it starts idling slightly faster, like in a warm up cycle.
Thanks in advance.
Thanks in advance.
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It should be idling fast, say around 8 to 900 RPMs at initial start up. At 300 I am surprised it doesn't stall out
Sorry I can't help, but here's a bump and I am sure someone will be along in a minute with the answer
Merry Christmas and Happy New Year
Jack
Sorry I can't help, but here's a bump and I am sure someone will be along in a minute with the answer
Merry Christmas and Happy New Year
Jack
Thread Starter
Safety Car
Joined: Aug 2000
Posts: 3,507
Likes: 0
From: Easton CA
Originally Posted by jackdaroofer
It should be idling fast, say around 8 to 900 RPMs at initial start up. At 300 I am surprised it doesn't stall out
Sorry I can't help, but here's a bump and I am sure someone will be along in a minute with the answer
Merry Christmas and Happy New Year
Jack
Sorry I can't help, but here's a bump and I am sure someone will be along in a minute with the answer
Merry Christmas and Happy New Year
Jack
Yeah, I was amazed that it would run too. Tonight, got in it at work, no problems at all, was idling just fine just after startup. Had to stop on the way home, idling just fine after startup again. I am at a loss.
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Yep, I don't know how to check the IAC, but it's usually the culprit when it comes to idle problems, basically it needs to be cleaned.Check out this site http://www.dvcorvettes.com/clean_air_passage.htm
Great site with helpful pics.
Great site with helpful pics.
Thread Starter
Safety Car
Joined: Aug 2000
Posts: 3,507
Likes: 0
From: Easton CA
Originally Posted by rick lambert
Yep, I don't know how to check the IAC, but it's usually the culprit when it comes to idle problems, basically it needs to be cleaned.Check out this site http://www.dvcorvettes.com/clean_air_passage.htm
Great site with helpful pics.
Great site with helpful pics.
Merry Christmas and Happy New Year!
Race Director
Joined: Aug 2003
Posts: 13,421
Likes: 8
From: Lake Mary Florida
It would not be IAC it is not in control upon first start. The O2 sensors when they become operational (proper temp) begin feeding valid data to the computer. It then controls idle via IAC based on O2 sensor data.
The computer ECM has several modes: Start, Clear Flood, Run, Acceleration, Deceleration, Batt-Volt Correction, and Fuel Cutoff.
Start Mode
When the ignition switch is turned to the On position before engaging starter, the ECM energizes the fuel pump relay for two seconds to allow the fuel to pressurize. The ECM then checks the Engine Coolant Temperature ECT, Throttle Position TP and Manifold Absolute Pressure MAP to determine the proper air/fuel ratio for starting. This ranges from 1.5:1 at -36 C (-33F) to 14.7:1 at 94 C (201 F) running temperature. The ECM controls the amount of fuel delivered in the starting mdode by changing how long the iinjectors are energized. this done by pulsing the injectors for very short times.
RUN mode
The run mode has two conditions called Open Loop and Closed Loop.
When the engine is first started, the engine spped is above 400 rpm the system goes into Open Loop operation. THe ECM ignores the signal from the O2 sensor and calculates the air/fuel ratio based on inputs from the ECT and MAP.
The system stays in Open Loop until the following are met:
1 The oxygen sensors O2 have varying voltage output showing that they are hot enough to operate properly.
2 The ECT sensor is above a spec ified temperature about 40C or 104F.
3 A specific amount of time has elapsed after starting the engine.
Specific values for the above conditions exist for each different engine, and are stored in the Programmable Read Only Memory (PROM). When these values are reached, the system goes into Closed Loop operation.
In Closed Loop operation the ECM calculatese teh air/fuel ratio (injector on time) based primarily on the signal from the O2s. This allows the air/fuel ratio to stay very close to 14.7:1.
I think first you should check your vacuum for leaks. Then check ECM grounds for clean, tight and proper ground.
Next:
Look at cleaning the throttle body.
Injector balance.
Fuel pressure issues.
EVAP control systems.
O2 sensors checks.
Additionals:
MAP sensor
Throttle linkage for sticking or binding
then IAC
I don't recall if you said if it hard started, or just fired right up and then idled badly. This assumes your talking about a cold engine.
The computer ECM has several modes: Start, Clear Flood, Run, Acceleration, Deceleration, Batt-Volt Correction, and Fuel Cutoff.
Start Mode
When the ignition switch is turned to the On position before engaging starter, the ECM energizes the fuel pump relay for two seconds to allow the fuel to pressurize. The ECM then checks the Engine Coolant Temperature ECT, Throttle Position TP and Manifold Absolute Pressure MAP to determine the proper air/fuel ratio for starting. This ranges from 1.5:1 at -36 C (-33F) to 14.7:1 at 94 C (201 F) running temperature. The ECM controls the amount of fuel delivered in the starting mdode by changing how long the iinjectors are energized. this done by pulsing the injectors for very short times.
RUN mode
The run mode has two conditions called Open Loop and Closed Loop.
When the engine is first started, the engine spped is above 400 rpm the system goes into Open Loop operation. THe ECM ignores the signal from the O2 sensor and calculates the air/fuel ratio based on inputs from the ECT and MAP.
The system stays in Open Loop until the following are met:
1 The oxygen sensors O2 have varying voltage output showing that they are hot enough to operate properly.
2 The ECT sensor is above a spec ified temperature about 40C or 104F.
3 A specific amount of time has elapsed after starting the engine.
Specific values for the above conditions exist for each different engine, and are stored in the Programmable Read Only Memory (PROM). When these values are reached, the system goes into Closed Loop operation.
In Closed Loop operation the ECM calculatese teh air/fuel ratio (injector on time) based primarily on the signal from the O2s. This allows the air/fuel ratio to stay very close to 14.7:1.
I think first you should check your vacuum for leaks. Then check ECM grounds for clean, tight and proper ground.
Next:
Look at cleaning the throttle body.
Injector balance.
Fuel pressure issues.
EVAP control systems.
O2 sensors checks.
Additionals:
MAP sensor
Throttle linkage for sticking or binding
then IAC
I don't recall if you said if it hard started, or just fired right up and then idled badly. This assumes your talking about a cold engine.
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Thread Starter
Safety Car
Joined: Aug 2000
Posts: 3,507
Likes: 0
From: Easton CA
Originally Posted by 93JetJocky
It would not be IAC it is not in control upon first start. The O2 sensors when they become operational (proper temp) begin feeding valid data to the computer. It then controls idle via IAC based on O2 sensor data.
The computer ECM has several modes: Start, Clear Flood, Run, Acceleration, Deceleration, Batt-Volt Correction, and Fuel Cutoff.
Start Mode
When the ignition switch is turned to the On position before engaging starter, the ECM energizes the fuel pump relay for two seconds to allow the fuel to pressurize. The ECM then checks the Engine Coolant Temperature ECT, Throttle Position TP and Manifold Absolute Pressure MAP to determine the proper air/fuel ratio for starting. This ranges from 1.5:1 at -36 C (-33F) to 14.7:1 at 94 C (201 F) running temperature. The ECM controls the amount of fuel delivered in the starting mdode by changing how long the iinjectors are energized. this done by pulsing the injectors for very short times.
RUN mode
The run mode has two conditions called Open Loop and Closed Loop.
When the engine is first started, the engine spped is above 400 rpm the system goes into Open Loop operation. THe ECM ignores the signal from the O2 sensor and calculates the air/fuel ratio based on inputs from the ECT and MAP.
The system stays in Open Loop until the following are met:
1 The oxygen sensors O2 have varying voltage output showing that they are hot enough to operate properly.
2 The ECT sensor is above a spec ified temperature about 40C or 104F.
3 A specific amount of time has elapsed after starting the engine.
Specific values for the above conditions exist for each different engine, and are stored in the Programmable Read Only Memory (PROM). When these values are reached, the system goes into Closed Loop operation.
In Closed Loop operation the ECM calculatese teh air/fuel ratio (injector on time) based primarily on the signal from the O2s. This allows the air/fuel ratio to stay very close to 14.7:1.
I think first you should check your vacuum for leaks. Then check ECM grounds for clean, tight and proper ground.
Next:
Look at cleaning the throttle body.
Injector balance.
Fuel pressure issues.
EVAP control systems.
O2 sensors checks.
Additionals:
MAP sensor
Throttle linkage for sticking or binding
then IAC
I don't recall if you said if it hard started, or just fired right up and then idled badly. This assumes your talking about a cold engine.
The computer ECM has several modes: Start, Clear Flood, Run, Acceleration, Deceleration, Batt-Volt Correction, and Fuel Cutoff.
Start Mode
When the ignition switch is turned to the On position before engaging starter, the ECM energizes the fuel pump relay for two seconds to allow the fuel to pressurize. The ECM then checks the Engine Coolant Temperature ECT, Throttle Position TP and Manifold Absolute Pressure MAP to determine the proper air/fuel ratio for starting. This ranges from 1.5:1 at -36 C (-33F) to 14.7:1 at 94 C (201 F) running temperature. The ECM controls the amount of fuel delivered in the starting mdode by changing how long the iinjectors are energized. this done by pulsing the injectors for very short times.
RUN mode
The run mode has two conditions called Open Loop and Closed Loop.
When the engine is first started, the engine spped is above 400 rpm the system goes into Open Loop operation. THe ECM ignores the signal from the O2 sensor and calculates the air/fuel ratio based on inputs from the ECT and MAP.
The system stays in Open Loop until the following are met:
1 The oxygen sensors O2 have varying voltage output showing that they are hot enough to operate properly.
2 The ECT sensor is above a spec ified temperature about 40C or 104F.
3 A specific amount of time has elapsed after starting the engine.
Specific values for the above conditions exist for each different engine, and are stored in the Programmable Read Only Memory (PROM). When these values are reached, the system goes into Closed Loop operation.
In Closed Loop operation the ECM calculatese teh air/fuel ratio (injector on time) based primarily on the signal from the O2s. This allows the air/fuel ratio to stay very close to 14.7:1.
I think first you should check your vacuum for leaks. Then check ECM grounds for clean, tight and proper ground.
Next:
Look at cleaning the throttle body.
Injector balance.
Fuel pressure issues.
EVAP control systems.
O2 sensors checks.
Additionals:
MAP sensor
Throttle linkage for sticking or binding
then IAC
I don't recall if you said if it hard started, or just fired right up and then idled badly. This assumes your talking about a cold engine.
It always fires right up but occasionally idles very slowly. For instance, no problems at all today, the idle was where it is supposed to be. When this extremely slow idle condition happens, it's with a cold engine and it seems to clear itself up after reaching operating temperatures. BTW, I checked the throttle body tonight and it's really dirty on the backside of the butterflies, so it looks like I have that to take care of after checking the vacuum and ECM grounds.
Thank you for the information.
Last edited by Oly; Dec 24, 2004 at 01:51 AM.
Race Director
Joined: Aug 2003
Posts: 13,421
Likes: 8
From: Lake Mary Florida
Your welcome. Try this as its easy and a quick isolation. Disconnect the neg battery cable for about 5 minutes. Reconnect, torque to 15Nm restart the engine with all accessories off and let it re-learn the parameters. About a 3 minute idle then turn everything back on and take it for a short drive. Monitor to see if it occurs again.
Thread Starter
Safety Car
Joined: Aug 2000
Posts: 3,507
Likes: 0
From: Easton CA
Originally Posted by 93JetJocky
Your welcome. Try this as its easy and a quick isolation. Disconnect the neg battery cable for about 5 minutes. Reconnect, torque to 15Nm restart the engine with all accessories off and let it re-learn the parameters. About a 3 minute idle then turn everything back on and take it for a short drive. Monitor to see if it occurs again.
I'll let you know how it goes. Thanks again.... Merry Christmas and Happy New Years to you and your family.
