What is this thing? It's mounted on the thermo housing. What will happen if it's removed?

 

With wires or with hoses attached to it?

 

Pic?

 

Well, Acually both, but mainly the one with wires.

 

here is the engine with the thermo housing plugged.

 

That provides engine temperature information to the computer. Without it, the computer will make incorrect decisions.

 

What kind of decissions?

 

Going closed loop instead of staying in open loop for one. In open loop, you aren't getting proper mixture and timing control, or torque converter clutch lock-up.

 

When mine was unplugged before it ran like crap and barely stayed running.

 

OK, that would explain the idle being at 500 rpm. Runs much stronger though. I just replaced 10 year old spark plugs, wires, cap and rotor. I also stripped all the emmissions junk and switched to a serpentine setup.

 

Ok, I put the sensor back on and it still idles low.

 

500 RPMs in drive is the factory spec for idle speed for LG4 3rd gens. However, the computer doesn't control idle speed. It can affect idle speed, but doesn't control it.

 

What all did you remove?

 

I removed the whole smog system, Heater core hoses, the charcoal filter canister and all hoses associated with it, that plastic ball thing that was near the charcoal thing. Plugged holes in exhaust manifold, intake manifold, and carb. I also changed from V-belts to serpentine.
500 rpm is in neutral.

 

coolant temp sensor. Did you replace it with a new one? They only run about fifteen bucks. Do you have any codes? Check your IAC valve. It may be dirty or need to be reset. Google on how to set the IAC valve/thirdgen