REGAL How to fix fast idle, 3.8 NA 2-bbl?

CaliWagon83

CaliWagon83

Royal Smart Person
Supporting Member
Nov 12, 2017
1,847
113
Orange County, CA
So, as you know, I got "Miss Piggy" up and running again, and successfully passed smog. However, a little more fine-tuning is still needed. The smog technician said there was a tube that I needed to connect. But since English wasn't his first language, it was a little hard to understand him. On the air intake snorkel, there is a little module that has what appears to be a small vacuum nipple, and when my father-in-law and I were replacing some of the vacuum lines under the hood last weekend, we did notice a small-diameter metal line that did not have anything attached to it. We followed the hose diagram as closely as we could, but may have mis-routed some of the lines, there are a few that are capped off as well. One of them appears to be an actuator for the cruise control. I'm just wondering if any of this might have something to do with the fast idle the car has right now. Even when warm, it seems like it idles at about 1,100 RPM (although that's a guess, since there's no tach). Even in gear, it idles on the fast side. If I had to guess, I'd say about 900 rpm. Doesn't matter if its fully warmed-up, it still idles fast. Will add photos later today.
 
Scoot-71

Scoot-71

Not-quite-so-new-guy
Nov 13, 2018
17
13
Rio WI
I think from what you described is the vacuum motor that runs a butterfly so it draws hot air off the exhaust manifold, helps the carb from frosting up.
 
airboatgreg

airboatgreg

Royal Smart Person
Oct 2, 2016
1,588
113
The module on the snorkel is the hot air intake for cold operation to prevent the carburetor base plate from icing and creating a stall condition in cool humid conditions. The vacuum hose connects to a sensor mounted in the bottom of the air cleaner housing. Probably not the reason for the fast idle. If it passed smog that tells me that the carbon monoxide and hydrocarbons are probably in check so that eliminates a vacuum leak, lean, rich condition so I would first look for a mechanical issue such as the fast idle cam sticking, throttle plate worn out, improper torque on the carb mounting bolts, improper idle setting or a wore out engine.
 
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CaliWagon83

CaliWagon83

Royal Smart Person
Supporting Member
Nov 12, 2017
1,847
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Orange County, CA
Well, it's more of an annoyance than anything. Car drives and runs fine otherwise.
 
jiho

jiho

G-Body Guru
Jul 26, 2013
576
43
When starting cold, I've always had to first stomp the accelerator to engage the choke, then start, then let the thing warm up until I can kick it down to slow curb idle with my foot. If I don't do this before starting out (and it can take a few in cold weather), then mine will behave as you describe.

If yours won't kick down to slow curb idle, then most likely either the idle stop screw is turned in too far, or the ISC nose switch is dead. The nose switch can be tested with the ohms setting on a multi-meter (see shop manual). If that checks out, try backing out the idle stop screw with the throttle resting on it.
 
CaliWagon83

CaliWagon83

Royal Smart Person
Supporting Member
Nov 12, 2017
1,847
113
Orange County, CA
Think I solved my own problem. When we put the carburetor back on, we forgot to reconnect the auto-choke wire. I went through some old photos I took when I removed the carb for the rebuild, and saw how it connected. Wasn’t able to take it out for a full shakedown run, but did the customary “two pump” cold start, and tapped the gas to take it out of cold start mode, and it seemed to settle into a lower idle.


 
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