i just got an 89 camaro with a 5.7 from a 89 blazer and when i looked under the hood the connector was off from the temp sensor so i reconnected it and the car doesn't idle right after driving for a minute or so because when i stop at a light or or just stopped in drive the idle goes up and down slightly and then wants to die but when i take the connector off it idles at about 900 to 1000 and is finebut check engine lights comes on when disconnected and turns off when reconnected my question is what could it be?

 

Assuming you are talking about the CTS (coolant temp sensor ) for the computer at front of intake then when it is disconnected , the computer puts engine into a "limp home" mode (why you have hi idle ) and lights the SES because it is not seeing the temp reading.

If engine runs cr*p with it connected ,then most likely it is faulty and giving the wrong temp reading to the computer.
$14 replacement
Same CTS for TBI/TPI/ LT1

 

Or, you have the 305 injectors sitting on top of the 350 engine; a guaranteed recipe for being WWWWWWAAAAAAYYYYYYY too lean at all times. Disconnecting the temp sensor will make the ECM fuel the motor as if it's -40° outside; basically as rich as it can possibly go; which is why it runs somewhat OK like that, but not when it's delivering the (much lesser) amount of fuel it's programmed to deliver when it's working right.

 

so how do i know if it is the wrong one and i changed the temp sensor but still the problem is there

 

Did you change the injectors or TBI unit?

 

I thought the tbi for a 5.0 is essentially the same as the 3.7 tbi.??

 

i have not changed the injectors i believe that tbi came out of the same blazer the 5.7 came out of

 

could it be the iac

 

you need to do some hunting around under the hood to verify the injectors and all the sensors and ECM chip are for the 350.

 

ive checked under the hood and almost all the connectors look newer and how do you know if the injectors belong to the 5.7 and when i got the car i found 2 other ecm in the trunk