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Engine idle question......


Tbarnes93

Tbarnes93

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Ever since I changed my head gasket my temp sensor has slowly stopped working. This morning it was around 25 degrees and my idle is all messed up when cold. It will go from little over 1k to 750. Would this be because my engine temp sensor isn't reading normal when truck is at operating temperature? We broke the sensor changing the head gasket. The electric connector was stuck. I'm also getting the 4.0 ohv tick on start up and it's very loud for about 5 seconds then quiets down. Any input or ideas how to fix these problems will be greatly appreciated. I'm off for the next 3 days so I'll be messing with it.
 


Tbarnes93

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It's a 1994 Ford ranger 4.0 4x4 btw
 

RonD

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There are 2 engine temp sensors, well 1 sensor and 1 sender.

The ECT(engine coolant temp) sensor has 2 wires, it is only used by the computer.
The ECT sender has 1 wire, it is only used by the dash board gauge.


At engine startup idle should go above 1,400 RPMs, then drop down to 900-1,000 RPMs if ECT reports cold, or drop down to 750 RPMs if ECT reports warm.
The high idle at start up is the computer testing the IAC(idle air control) valve, then waiting for data from ECT, idle should drop within 2 or 3 seconds to cold or warm levels.

I assume you mean idle goes from 1,000 to 750 RPMs too fast??
So IAC/computer are working but ECT is reporting warm temp, not cold, so warm idle is set when it should be cold idle.

ECT sensor is easy to test with OHM or Volt meter
Read here:
http://oldfuelinjection.com/?p=28



You make have a sticky lifter that is causing the tap, or a broken spring in the lifter.
Hydraulic lifter loses pressure when it sits, then takes a few seconds to "pump up" after start up.
You should try some Lucas or similar oil treatment.
Or if you are going to change the oil soon, add a 1/2 quart of ATF(high detergent oil) and run engine a few hundred miles with that, then change oil.
 
Tbarnes93

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its the engine coolant temp sensor that is broke.
 
Tbarnes93

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and i mean the idle will idle high like its cold then down like its warm until it is actually warm. about 3-4 miles of driving.
 
Tbarnes93

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I put some engine flush in and changed the oil and out a qt of Lucas in it working great now
 
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