The cold start time switch and the cold start injector are active only when the key is in the start position. If the engine is cold enough, it squirts extra gas into the intake manifold.
I suggest that you check the engine coolant temp sensor. It should have:
10-20 k ohms at -4' f
4-7 k ohms at 32' f
2-3 k ohms at 68' f
It should have 5 volts on one pin, and about a volt or less on the other pin with the key on and the engine at operating temperature.
Let me know what readings you get.
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Lets check the air flow meter next. The coolant temp sensor is working.
From the yellow-green wire to the brown-black wire on the air flow meter, the specs are:
10k-20k ohms at 4'f
4k -7k ohms at 32'f
2k-3k ohms at 68'f
There are two vacuum switching valves on the engine. Have you done any testing on them?
When you say wire color yellow green where is that wire at? Is it coming from the temp. sensor to the black brown wire on the air meter? You also said there are two vacuum swithing valves on the engine? On this engine the only other one I see is the one valve for making the engine idle faster when the AC is on.
There is a green- yellow and a yellow green on the mass air sensor.
Green yellow means the wire is mostly green with a yellow stripe. Y G is mostly yellow.
It should be the last pin on the air flow meter. It's the yellow-green wire. The one on the other end of the connector is green-yellow. Very easy to confuse. There is a yellow-blue wire next to the yellow green.
My book shows the fuel pressure up solenoid on the back of the engine, passenger side. It has a green wire and a white-red wire. Have you tried powering up the idle up solenoid to see if it works and picks up the engine speed?
Either the problem is:
Not getting power from the engine control unit to the idle-up solenoid because the computer thinks that it's not needed.
Getting power to the solenoid but no ground
Getting power and ground but not activating the idle-up solenoid
Activating but not letting air pass through.
Both the air temperature sensor in the air flow meter and the coolant temperature sensor tell the computer what the temperature is and if idle-up is needed.
It's a process of elimination. I always start with sensors because they fail more than anything else. But next check the solenoid by first, checking for power and ground when it's supposed to be activated.
The air temp sensor is an integral part of the mass air sensor.
That reading would tell the computer that the temperature is about 68 degrees. Is that correct?
I went through the entire wiring diagram for the truck and white - red is a 12 volt wire with then key on that goes all over the engine compartment. Yellow is used on a couple of different circuits, the throttle position sensor, the alternator (sends the signal to the dash warning light), from the cruise control computer to the relay, and from the little square check connector under the hood to the computer.
I couldn't find anything with both the yellow wire and a white - red wire.
So now we know that the solenoid works and the ECU works. So it still comes down to inputs or to the ECU or a faulty ECU.
The thing to check now is to back probe the ECU and see if you are getting the same readings at the ECU as at the sensor. If not, there is a broken wire between the sensor and the ECU, or a bad connection at the ECU. Using the same color code of the wires, check resistance at the back of the ECU.
The most common cause of a problem is with the connectors at the back of the ECU. If you have to rock the connector to get it disconnected from the ECU, it's common to stretch the connectors out and cause an open circuit. I use a piece of piano wire to test the tension on the connectors. Be gentle, it's really easy to stretch out a connector with too big of a piece of wire.
All of them. Since they all go to the ECU, it won't take too long. But it's looking like the signal from one of the temp sensors (air or coolant) may not be getting to the ECU, so the ECU doesn't turn on the idle-up solenoid.