What would cause a N/A 86 to not fast idle (do the 3k for 20 sec.s) when its cold, but it will do it when it's warmer outside. It still goes up to 1.5k rpms, just never goes up to 3.

 

Bad temp switch on the bottom driver side of the rad.

The system is widely regarded as stupid. It puts immediate unnecessary strain on a cold engine. Mostly it's there to light off the cats. Instead of replacing the switch, jumper the two wires together.

 

Where in MO are you?

 

The water temp switch does not *make* til 62*. So forget about it happening prior to the water temp getting up to that figure. See FSM.

EDIT: Actually, the above is NOT the answer at all. Sorry 'bout that. What casues the 17 second event is the Air Bypass Relay pulling in and opening the Air Bypass Solenoid valve for 17 seconds.

You can confirm this by looking at the FSM (THE 86/87 FSM, NOT the 88 FSM) and the Bypass Air Control System (BAC), where they pull the plug on the water thermo SENSOR and install a 2K ohm resistor in the plug (2K represents approx 65*) and after doing so confirm that the Air Bypass Solenoid pulls in for 17 seconds. Note that the BAC itself also opens up during that period. It's a combination of BAC and Air Bypass Solenoid opening for 17 sec that causes the high idle for......17s.

Water temp switch on the radiators bottom controls the Relief solenoid not getting energized til the water temp gets up to ? 65* or so.

 

If your water temp is lower than 59* or above 98*, then that seventeen second event should not happen. I suspect the water temp in your area has been under 59* overnight and that's why the event has not been happening. See attached jpg.

 

Hour south of Kansas City, MO.

So if its too cold, then it won't do the fast idle? And yes, it's most certainly colder than 59 degrees.

 

if it's idling at 1.5k you have plenty of fast idle.

 

Anything under the 59* or over 98*F should not result in the seventeen second rev b/t 2000-3000 rpm.

But you should have a idle of around 1300rpm when you start a cold engine because the water thermowax should be holding the throttle plates open a bit, til the engine water warms up sufficiently.