dying at idle after 58mm throttle body?

i put a 58mm professional products tb on my 97 ss after a nitrous backfire that bent the throttle blades on my stock one...i also replaced the maf sensor and the intake air temp sensor..... i adjusted the idle screw and slotted the tps and set the voltage.... it wont idle still ... it dies...and when you start it back up the iac count is maxed out... i'm about to put a stock tb back on it because i dunno if the 58 is just too big or what? ...maybe bad iac? btw its a 10.5:1 383 with stock ported heads 238 242 @.050 58X 59X lift with 1.6s every bolt on available...tuned with lt1 edit... is the tb too big? does it need to be tuned for the tb?

What do you mean you adjusted the IAC? Are you talking adjusting the throttle blade screw to open the blades a bit more then stock, cause thats what the 383 would need. Then readjust the TPS. Usually the blades being closed too much would cause it to die at idle. When the blades are adjusted open more and the TPS readjusted to .67v (i think thats about right), your IAC counts should be low, so its weird that there maxed. Could the IAC have been damaged also during the backfire?

Ken R.

What do you mean you adjusted the IAC? Are you talking adjusting the throttle blade screw to open the blades a bit more then stock, cause thats what the 383 would need. Then readjust the TPS. Usually the blades being closed too much would cause it to die at idle. When the blades are adjusted open more and the TPS readjusted to .67v (i think thats about right), your IAC counts should be low, so its weird that there maxed. Could the IAC have been damaged also during the backfire?

Ken R.

i adjusted the idle screw and the iac count was good... then when the car starts back up it is maxed out again... checked it with a tech 2... did it several times... the tps voltage is like .68 so thats good... i dunno whats wrong with it ... didn't do this till the bigger throttle body was put on ... and the iac isnt the one that was on when it backfired... it was off another throttle body that came off a running car..

Did you check all the parts that were exposed to the backfire for damage, like the MAF sensor, MAP sensor, inlet bellows, etc?

Are you sure the IAC motor is working? The PCM only tells you what "counts" it wants the IAC motor to open to. It has no way of knowing whether the motor is moving or not.

i adjusted the idle screw and the iac count was good... then when the car starts back up it is maxed out again... ..

Not sure I understand. The engine has to be running for throttle screw adjustments to affect IAC counts. You might also try an IAC reset (http://shbox.com/1/4th_gen_tech2.html#iac_reset).

Did you check all the parts that were exposed to the backfire for damage, like the MAF sensor, MAP sensor, inlet bellows, etc?

Are you sure the IAC motor is working? The PCM only tells you what "counts" it wants the IAC motor to open to. It has no way of knowing whether the motor is moving or not.
the maf iat and everything is all new i havent checked the maf sensor ... the intake elbow is aluminum and i checked it for cracks... no vacum leaks its got plenty of vacum no broken valvetrain parts...

Not sure I understand. The engine has to be running for throttle screw adjustments to affect IAC counts. You might also try an IAC reset (http://shbox.com/1/4th_gen_tech2.html#iac_reset). i adjusted the screw while it was running.. i've reset the iac several times and the car won't learn idle ... if i take off in first gear and turn the key off and back on (with the clutch engaged) the car idles but when i'm drivin and i push the clutch or put it in nuetral the rpms only come down to 1500 and slowly creep down ... i've just been doing that so it doesnt die every time i stop

Have you checked the throttle body IAC passage for casting flash?

Have you checked the throttle body IAC passage for casting flash?

no i haven't ... whats that

It's material left over from the casting process. May be some the IAC ports that could be disrupting air flow and messing with the IAC. Since thats a Professional Products part (made in china), i'd probably double check that also since there probably just cranking them out the door on the cheap.

Ken R.

k i took the tb off and looked at it cleaned it and put it back on ... still the same crap going on... could the map sensor cause it to do this?

did this one get resolved? I am having the exact same problem. tps is at .63 volts and iac is maxxed! and i have to hold pedal to keep it idling