fast idle understanding

[Stephen B.]

Good morning. In the process of getting my 72 coupe on the road after 16 years, and yes a lot of working doing so, I ask this question. The TCS system is inop, the fast idle solenoid is inop. I jumped this too see if it work and does. How does this work, and where would be a good place to wire in? Thanks.

[Mike E.]

Re: fast idle uinderstanding

I am not sure I understand your question. The proper place to wire it in is to use the original wiring. If that is no longer present, you want to duplicate the original. If you are trying to bypass it, that is another story.

[Duke W.]

Re: fast idle understanding

Good morning. In the process of getting my 72 coupe on the road after 16 years, and yes a lot of working doing so, I ask this question. The TCS system is inop, the fast idle solenoid is inop. I jumped this too see if it work and does. How does this work, and where would be a good place to wire in? Thanks.

The solenoid has nothing to do with the fast idle. Its better referred to as an "idle stop" solenoid. It retracts when you turn off the ignition to prevent engine run-on that can occur due to the higher idle speed and retarded total idle spark advance of emission controlled engines of that era.

You need to spend some time reading the CSM to understand the emission control systems and carburetor adjustments. The fast idle system is built into the Q-jet. The specified fast idle speed is set with the engine fully warmed up, and on an initial cold start it will be 2-300 revs lower.

Duke

[Patrick H.]

Re: fast idle understanding

The solenoid has nothing to do with the fast idle.
Duke

Correct, but it is used to set your idle speed - which is done when warm.

As Duke notes, take a look at the CSM to see how it's set up.

[Edward J.]

Re: fast idle understanding

Good morning. In the process of getting my 72 coupe on the road after 16 years, and yes a lot of working doing so, I ask this question. The TCS system is inop, the fast idle solenoid is inop. I jumped this too see if it work and does. How does this work, and where would be a good place to wire in? Thanks.

Stephen, The 72 TCS system works a little differntly depending on if you have a automatic transmisson or a 4speed.

[Duke W.]

Re: fast idle understanding

Correct, but it is used to set your idle speed - which is done when warm.

Yes, you turn the hex head to set normal hot idle speed. My '72 Vega GT has a similar setup. The recommended hot idle speed set with the solenoid was 1200! Then when you shut off the ignition the solenoid retracted to close the throttle so it wouldn't run on. It wasn't long before I disconnected it and just set the hot idle with the carb throttle adjustment screw to 700.

Duke

[Stephen B.]

Re: fast idle understanding

Stephen, The 72 TCS system works a little differntly depending on if you have a automatic transmisson or a 4speed.

ED, the car is an auto. The question I am asking is what powers the fast idle solenoid? According to wire manual this runs thru the TCS, which mine had been taken out, so will just a hot 12 volt from the tcs wire work?

[Mark E.]

Re: fast idle understanding

As Duke stated earlier, it's an idle stop solenoid, not a fast idle solenoid. For 72, 73 and maybe a couple of more years it was energized by a single lead (tan?) that's part of the engine wiring harness. Look for it; someone may have tucked it away.

TCS uses a separate "jumper" harness that plugs into the engine harness. Note that 71 has a unique CEC system which combines the TCS and idle stop solenoids.

The idle stop solenoid is energized when the ignition is on.

[Edward J.]

Re: fast idle understanding

ED, the car is an auto. The question I am asking is what powers the fast idle solenoid? According to wire manual this runs thru the TCS, which mine had been taken out, so will just a hot 12 volt from the tcs wire work?

Steve , the TCS system works on a 72 auto car is, with a temp. sender mounted in the pass. side cylinder head (between rear two plugs) On the auto cars on a cold start when reverse gear is selected- there is a delay relay that comes on after about 15/20 seconds and then energizers the vacuum solenoid turns on and the solenoid on carb. if you listen closely you will hear the ilde speed increase slightly(this is the vacuum solenoid applying vacuum to the advance on distributor. also note it seems that the solenoid on carb does not seem to over power the carb. return spring so if you just touch the accelerator pedal the solenoid will extend.