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The looping up and down in idle speed is most likely a problem with the idle air control valve (IAC). The idea that the coolant temperature sensor was an issue is not too far off. It tells the computer the coolant temperature, and from that, the computer determines how rich or lean to make the fuel mixture. With that in mind, I would suggest getting a live data scanner. Scan through to the coolant temperature sensor and see if the reading is correct. The temperature indicated should be very close to the ambient temperatures outside (if the car was cool and not used).
If that turns out to be good, the next thing I would check is fuel pump pressure. The idea that runs worse when under a load may indicate weak pressure from the pump. Here is a link that shows in general how to check pressure:
Here are the directions specific to your vehicle for checking the fuel pump. At the end, it indicates what the manufacturer's specifications are to be.
WARNING: Before disconnecting any fuel line, release fuel pressure. When replacing fuel system components, keep sparks, cigarettes and open flames away from fuel. Plug hoses while they are disconnected.
1. Disconnect negative battery cable.
2. Connect fuel pressure gauge between filter and main fuel hose.
3. Connect battery cable.
4. Start engine and run at idle.
5. Line pressure should be 30 - 38 psi (206 - 265 kPa).
6. Disconnect vacuum hose at pressure regulator. Line pressure should now be 37 - 46 psi (255 - 314 kPa).
For the idle issues, here is a general overview of the IAC and directions on replacement.
The IAC or idle speed control is located under the throttle body. Take a look at pic 1. Make sure it's connected and no damage was done to the wiring. Here are the directions to test the IAC / ISC. The remaining pic correlate with these directions.
COMPONENT TESTS AND GENERAL DIAGNOSTICS
1. Connect jumper wire between diagnosis connector TEN and GND terminals.
2. Connect a tachometer.
3. Start engine.
4. Idle speed should gradually decrease as engine warms up and air valve closes.
IDLE SPEED CONTROL (ISC) VALVE
Idle Speed Control (ISC) Valve Testing
1. Unplug ISC valve connector.
2. Measure resistance across terminals. It should be 10.7 - 12.3 ohms @ 68 F (20 C).
3. If not as specified, replace valve.
Let me know if this helps or if you have other questions.
Images (Click to enlarge)
Monday, August 27th, 2018 AT 6:18 PM