I have a 1970 Pontiac 350 with 4bbl, that was originally a 2bbl from the factory. I do NOT have AC, should I still have an idle stop solenoid? Also, I understand there may be some electronic switch that connects to the transmission to aid in shifting over and above the vacuum, is this correct? I have a turbhydramatic trans. Thank you!

John Mader

Asked by Sep 01, 2014 at 08:47 AM about the 1971 Pontiac Le Mans

Question type: General

3 Answers


Yes, the solenoid that you're talking about is not and idle speed up device. It's an anti-dieseling solenoid. The solenoid is supposed to be energized whenever the ignition is on. The throttle lever on the carburetor is supposed to rest on the plunger, which will be extended. When you switch off the engine the solenoid is de- energized, the plunger drops back and closes the throttle plates to prevent dieseling (run on) after the ignition is turned off. The electronic switch on the transmission is the kick down switch. When the throttle is pushed down about 3/4 a solenoid in the transmission activates to downshift the transmission for faster passing and acceleration. Also, your car was originally equipped with an emission control device called transmission controlled spark (TCS). This system only allowed vacuum advance to the distributor when the transmission shifted into high gear, or the engine coolant temperature was below 80°F or above 220°F. This system consists of a switch on the transmission, a vacuum solenoid in the vacuum line to the distributor and a 3 way cooling system temperature sending unit (with warning light) or 2 separate cooling system sending units (with gauge package ). HTH. -Jim

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John Mader

Is it ok to not have the TCS system? The car runs ok, never kicks down from 3 to 1, will do 3 to 2 for passing. Also, has a hard time idling in gear. Any of these issues sound like they could be a result of not having the TCS? Thank you!

1 out of 1 people think this is helpful.

I doubt that not having the TCS hooked up would cause those problems. Quite honestly most TCS systems were disconnected years ago. Simply because not many people knew what it was. To properly adjust the idle speed that anti-dieseling solenoid needs to be energized. There should be an adjustment screw there to move the whole solenoid assembly to adjust the idle speed. In drive, with the vacuum advance hose at the distributor disconnected and plugged, the idle should be 600 RPMs. Once you put it in park you'll notice that it seems to idle too fast. My '70 Catalina was like that too. It's normal. That's why the anti- dieseling solenoid was put there. To close the throttle plates when the ignition is turned off and prevent run on. A 3 to 2 downshift is normal. I've never had a turbo- hydramatic 400 downshift from 3rd to 1st. I don't think it's supposed to. I could be wrong on that. But I've never experienced it. Thank you for the best answer click as well! HTH. -Jim

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