I have an 87 iroc with the 350 all stock. First problem is the service engine light is on. I am getting code 23 which refers to the manifold air temp sensor. I replaced the sensor and it has not solved the problem. any suggestions?

Second is this noise that occurs once the car warms up and is taken for a short drive. it goes away with increased throttle input. I want to say its the smog pump but not sure. heres a vid.

http://vid11.photobucket.com/albums/...ps516d9fb3.mp4

btw what should idle be when car is warmed up?

 

that sound is the air pump, quite normal for them to do that.they have a "muffler" that's probably going bad. and hot idle in drive should be 750 RPM

 

is it something that can be fixed or does the pump need to be replaced? what would happen if i just take to belt off and not completely remove it?

 

well, taking the belt off will confirm that its whats making that noise. and if your state allows, it wont hurt to just leave the belt off. sometimes when smog pumps are failing. they make that noise. good thing is , they aren't expensive to replace.

 

took belt off to confirm and solved that problem. anyone has any suggestions on the code 23 issue? guessing there's a short in the wire? is there any test i can run ont wire and or sensor?

 

FSM says,, check the MAT , if over 25,000 ohms,replace MAT. check the wiring going to the sensor.also a failing VSS can cause a code 23. also a failing ECM can cause a false 23.

 

ive read that it could be the TPS as well but checked that and seems to be working fine. i can start the car let it idle in the driveway and the light will eventually come on. i can also start the car and go for a drive and the light will not come on until i put it in park and let it sit. i dont know. ill see if i can figure it out. is there a link to download the fsm on here? btw thanks for your help.

 

I bought mine online at "helm inc". as I prefer to have the actual hard copy.and from your description ,yout MAT sensor is bad.the downside is you have to remove the plenum to replace it.

 

That was the first thing I did. see first post. unless the new one is bad thats not the problem.

 

Could be the connector/pigtail. I had a code for the coolant temp sensor, I replaced the sensor and still had the code, replacing the pigtail solved my problem