proper idle speed
Thread Starter
Heel & Toe
Joined: Sep 2019
Posts: 18
Likes: 0
proper idle speed
have a 1990 C4 of course and have a high idle issue. was in the Chevy dealership and asked them to set idle at proper speed.. it does have a 52 mm BBK TB. has headers with Corsa exhaust. a decent air filter also. was told i could not slow the idle down without the stock TB on it . i have to think that s little larger throttle body would not make it impossible to set idle correct.
Safety Car
Joined: Sep 2001
Posts: 4,157
Likes: 554
From: Glenbeulah Wi
-Warm engine up
-Turn off
-Jump the A to b terminal in the diagonistic connector together
-Turn key on and get out and disconnect the idle air connector on the thottle body
-Turn key off
-Pull out jumper
-Start car and adjust the idle screw on the BBK throttle body until you have 550 RPM at warm idle
-Turn car off and plug connector back in
Good to go
-Turn off
-Jump the A to b terminal in the diagonistic connector together
-Turn key on and get out and disconnect the idle air connector on the thottle body
-Turn key off
-Pull out jumper
-Start car and adjust the idle screw on the BBK throttle body until you have 550 RPM at warm idle
-Turn car off and plug connector back in
Good to go
Team Owner
Joined: Jul 2004
Posts: 28,464
Likes: 3,288
From: Hartford WI
I much prefer to set it using the IAC counts since it also warns me of an air leak if I cannot adjust it. You can set the idle speed by going through the ECM. If the program is right, I would try find the problem in the system. At closed loop and idling with everything but the motor off, I scan the IAC counts. Target is 20-30. If it is more than 30, the ECM needs air. Turn the screw in and rev and recheck after it settles down. If it is less, turn the screw out, rev and recheck. This would bypass all the guesswork. The FSM method relies on a perfect system. No leaks, everything is functioning INCLUDING THE TACH which might not be accurate.
