1972 - LT1 --idle

[Jerome E Pederson]

The idle on my car after running the car for 15 to 20 minutes or at least until the engine coolant reaches 180 degrees, drops to 300/400 RPM's and really struggles to stay running without working the throttle The carb has been rebuilt by Holley and is the correct carb for the car. The car is equipped with A/C. However, with or without the A/C running this idle problem happens.

Once the engine cools, from not running, The engine will idle properly both the initial fast idle and then the normal idle at 800RPM's. Then after driving it for 10/15 minutes the engine will struggle to idle without working the throttle.

Any help or thoughts.

Jerry

[Patrick H.]

Re: 1972 - LT1 --idle

Does your car have the idle solenoid installed? See photo below - different carb and bracket but the solenoid is the same.

To me it sounds like either a) the solenoid is misadjusted, or b) the solenoid is not present but your idle is set as if the solenoid is still there.

Correct idle setting is done via the idle solenoid for 1972, and the carb is SUPPOSED to go down to 400rpm or so if the solenoid is off. Essentially this allows for closing of the throttle blades and was GM's trick at "anti-dieseling" for 1972.

Patrick

[Patrick H.]

Re: 1972 - LT1 --idle

Does your car have the idle solenoid installed? See photo below - different carb and bracket but the solenoid is the same.

To me it sounds like either a) the solenoid is misadjusted, or b) the solenoid is not present but your idle is set as if the solenoid is still there.

Correct idle setting is done via the idle solenoid for 1972, and the carb is SUPPOSED to go down to 400rpm or so if the solenoid is off. Essentially this allows for closing of the throttle blades and was GM's trick at "anti-dieseling" for 1972.

Patrick

[Jerome E Pederson]

Re: 1972 - LT1 --idle

Yes, I do have the the idle solenoid installed and there is electrical power at the unit. What condition would warrant this solenoid to be off (not turned on)?

Jerry

[Jerome E Pederson]

Re: 1972 - LT1 --idle

Yes, I do have the the idle solenoid installed and there is electrical power at the unit. What condition would warrant this solenoid to be off (not turned on)?

Jerry

[Terry M.]

Re: 1972 - LT1 --idle

Does the solenoid shaft extend when power is present? You may have to "help it along" by moving the throttle linkage slightly. There is always the chance that the solenoid has failed.

[Terry M.]

Re: 1972 - LT1 --idle

Does the solenoid shaft extend when power is present? You may have to "help it along" by moving the throttle linkage slightly. There is always the chance that the solenoid has failed.

[Dick W.]

Re: 1972 - LT1 --idle

First step would be to see if you have a 12V power source to the solenoid when the ignition is on. It is possible that the solenoid is defective. It shoud engage when 12V is put to the terminal. I have seen a couple over the years that did not have the ability to kick the throttle up. Be sure when you start the car to open the accelerator slightly when it starts. This allows the solenoid to travel to the proper position.

[Dick W.]

Re: 1972 - LT1 --idle

First step would be to see if you have a 12V power source to the solenoid when the ignition is on. It is possible that the solenoid is defective. It shoud engage when 12V is put to the terminal. I have seen a couple over the years that did not have the ability to kick the throttle up. Be sure when you start the car to open the accelerator slightly when it starts. This allows the solenoid to travel to the proper position.

[Patrick H.]

Re: 1972 - LT1 --idle

As Terry and Dick noted, if you have power it "should" turn on whenever you turn the key to the ON position. You may have to play with it to see what's happening. In addition, you may have to turn it (extend it - there's a reason it's shaped with a hex head) to raise your idle when the car is warm, and go from there.

Your would not be the first to need some "Viagra" to "get it up" and working.

PH

[Patrick H.]

Re: 1972 - LT1 --idle

As Terry and Dick noted, if you have power it "should" turn on whenever you turn the key to the ON position. You may have to play with it to see what's happening. In addition, you may have to turn it (extend it - there's a reason it's shaped with a hex head) to raise your idle when the car is warm, and go from there.

Your would not be the first to need some "Viagra" to "get it up" and working.

PH

[Jack H.]

Follow the book...

Your copy of the 1972 Chassis Service Manual (CSM) should give you a theory of operation thumbnail regarding the TCS emission system as well as correct setup for the car's curb idle speed.

Basically, you disconnect the idle stop solenoid and set the warm engine, idle RPM on the carb according to the table in the CSM (or on your emission label under the hood). Then, you reconnect the idle stop solenoid and FORCE the TCS system to fire (solenoid engages with the carb's linkage) and adjust the solenoid's shaft length to achieve the 'Delta RPM' spec'd in the table in the CSM.

Last, with the engine warm and the TCS solenoid inactive, force the carb's choke linkage onto the cam step specified in the CSM and adjust the cold idle RPM according to the table. Now, you should have all three curb idle settings properly tweaked...

[Jack H.]

Follow the book...

Your copy of the 1972 Chassis Service Manual (CSM) should give you a theory of operation thumbnail regarding the TCS emission system as well as correct setup for the car's curb idle speed.

Basically, you disconnect the idle stop solenoid and set the warm engine, idle RPM on the carb according to the table in the CSM (or on your emission label under the hood). Then, you reconnect the idle stop solenoid and FORCE the TCS system to fire (solenoid engages with the carb's linkage) and adjust the solenoid's shaft length to achieve the 'Delta RPM' spec'd in the table in the CSM.

Last, with the engine warm and the TCS solenoid inactive, force the carb's choke linkage onto the cam step specified in the CSM and adjust the cold idle RPM according to the table. Now, you should have all three curb idle settings properly tweaked...

[Gary Schisler]

Agreed and...

Iirc, the 1972 GM Service Manual has a good desription of the emissions controls on the 72. It gives emissions information as well as some troubleshooting guides for emissions and the TCS system.

Gary

[Gary Schisler]

Agreed and...

Iirc, the 1972 GM Service Manual has a good desription of the emissions controls on the 72. It gives emissions information as well as some troubleshooting guides for emissions and the TCS system.

Gary