j.kenzie@sbcglobal.net

Hi guys,
In the course of fixing vacuum leaks and adjusting my idle position switch, I have developed a strange problem. When I start my cold engine, it goes to high idle of about 1800 RPM's then drops to 600-700, then does it again and again. If I move the throttle off the idle stop, it no longer pulsates. Once it warms up for 2 minutes and the RPM's drop to normal idle speed of 900 RPM, everything is fine. I guess there's a RPM cutoff when on the idle switch, but this is new, and wondered if anyone had any ideas to eliminate it.
Thanks,
Dave

Majestic Moose

Check for power getting to the aux air valve. Remove the air box for access to the connector. You should have 12v to one of the pins with engine running.

This was my symptom.

j.kenzie@sbcglobal.net

Thanks, Alex. That is exactly what I'm seeing. I tried disconnecting the AAV and no difference. That may either confirm or rule out your diagnosis, depending on how the AAV works.
I will check.
Dave

gazfish

My suggestion is your idle is set too high and it's going into overrun mode, this is good as it indicates your idle switch is adjusted correctly. Try turning the bypass screw clockwise to reduce the idle a bit.
The AAV closes slowly as the engine warms up it doesn't actively adjust the idle the way later years do.

j.kenzie@sbcglobal.net

Thanks, Gaz. I tried that, but it gets the idle a little too low, especially for my alternator output voltage.
Dave

AirtekHVAC

Huh, my 82 was doing the EXACT same thing....somehow I fixed it, and now it doesn't run at all.....

Something else to check, thanks....

Majestic Moose

Disconnecting it will not show an instant result.

How it works is that the valve is open without power or at cold temperatures, letting extra air into the intake. Power is applied through the fuel pump relay and it heats up a bi-metallic strip which closes the valve over a couple minute time period. If it is not getting power, it will still close through heat soaking via engine bay heat but will take 15-20 minutes, much more than the two minutes you indicate.

You need to check for voltage at the plug to diagnose. It may be easier to check with engine off. Pull the fuel pump relay and jumper 30 to 31b, ignition may need to be on, I do not remember, but that will energize the wire letting you test without dealing with the engine noise and heat.

Otherwise, 900rpm is a bit high of an idle, should be 750 +/- 50. You may have developed a small intake air leak?

j.kenzie@sbcglobal.net

Thanks, Alex. I think you are right on the money. I purposely set my idle a little high, but I can indeed set it down to 750.
Because of my SC, I have bypassed my Thermotime switch so I only get cold start injection while cranking. (The SC main intake elbow interferes with the TT switch connector.) I will need to come up with a work around for the AAV.
Thanks again,
Dave

j.kenzie@sbcglobal.net

OK. The AAV has nothing to do with the thermotime switch. It seems to have a direct connection to the fuel pump relay. I think Alex mentioned that, but it did not sink in. I will look for 12 volts at the AAV, which should be there as long as the fuel pump is running.
Thanks,
Dave

The Forgotten On

The thermotime switch directly controls the cold start injector. If it is disconnected it simply wont fire at all.