Fast Idle Circuit

[afgunn]

Please inform/correct as needed.
On the '93 below my fast idle does not work and best I can tell it is the switch in the rear of the RH head - it is open at ~75*F. From previous posts I gather that the switch should be closed below 120*F or certainly below 100*F. Is there any source for this switch other than the dealer? PNs?

Also, contrary to what I have read here (and read in my Haynes Manual) my HPCA does not operate off of this same switch above. This has been confirmed by checking the circuit wiring - there is no connection between the switch and the HPCA connector. And my HPCA IS working while the fast idle is NOT (the fast idle solenoid IS good). Does anyone know how the HPCA works on my '93?

[afgunn]

A PN or at least the proper name for this switch is a must now. I have been to the dealer and we could not identify it. And neither could 2 major parts stores. Thanks in advance for any help!

[JohnC]

IIRC, my '93 (6.5) had a single (green?) wire that fed both the fast idle and the HPCA solenoids. Didn't need a meter to see that they both ran off the same circuit...

[afgunn]

Thanks for the reply.

On mine there is a pale green wire going to the HPCA and a dark green wire going to the fast idle. The HPCA has 12v and the fast idle does not all while the switch is open (bad). There are only 2 wires on the temp switch: 12v and the dark green going to the fast idle. No continuity between the wires on the HPCA and fast idle.

[JohnC]

Hmmm... I'm pretty sure mine were daisy-chained together.

[afgunn]

Well, it took 2 days and some searching on the internet but I got the nomeclature and then I was able to get the PN from GM. It makes sense now that I have the info. Is that not the way it usually goes!?

Diesel Cold Advance Switch:
GM: 10154649
KEM Parts: TW147

[rhsub]

On a lLight duty engine the HPCA is controlled by the glow plug inhibitor relay which also controls the glow plug relay, check if it operates when the glow plugs are on
On a heavy duty engine it operates off the same wire as the fast idle solenoid which is powered from the temp switch at the rear of the right head, switching temp is 80F
I would be tempeted to jump a wire from the fi solenoid to the hpca terminal and use it that way
I think the glow plug inhibitor relay is on the passenger side firewall
Ron
j