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On my 72K 95 LT1, It won't start (just cranks) until I unplug the temp sensor at the water pump.
Then is starts and will run fine. Plug it back in and the motor hunts up and down and either races or stalls.

I replaced the temp sensor and cleaned up the connector. Also replaced Fuel pump. sending unit, egr valve (was bad), checked Opti vent harness.

It has to be some sort of sensor issue. Any ideas?
 

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Did you check all of the connector pins that run through the wiring to the computer. Check the ground for the computer. You may have a bad computer as well.
 

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Do the fans turn on when you pull the connector?
 

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Instead of throwing parts and time at the issue find a way to get some live data.


Fred has given you the best tests for a temperature sensor problem.


If the sensor wire was broken(not connected) your fans would be running even at a cold start, just like you unplugged the sensor. If you have some other engine issue, AND the temperature sensor and wire are good unplugging the temperature sensor forces the PCM to provide a very fuel rich start.and idle.When the PCM gets temperature information it will lean out the fuel even in open loop.


The temperature sensor may not be a problem at all. You may have a IAC problem or something else.
 

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I agree with others, live data would be your best bet to narrow down the problem without throwing parts at it.

However, to diagnose the IAC, press throttle about 10-20%, keep your foot steady and crank it. If it starts and runs fine with your foot still on the pedal a little, see if you can loosen your foot a little to maintain an idle-ish speed, like 700 RPM. If holding it around that speed keeps the engine steady, then it sounds like the IAC.

I laymen's terms, unplugging a sensor causes the computer to use static tables for fuel and air mixtures and ignore some sensor inputs, which may be rich enough to keep it running if your IAC is stuck.
 
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