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idlesurge [2012/07/17 15:51]
dmertz
idlesurge [2016/01/12 18:41]
nickracer [Throttle-body problems]
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 ===== Throttle-body problems ===== ===== Throttle-body problems =====
  
-The simplest path through the throttle body is the Basic Idle Speed Screw (BISS). ​ This screw controls an otherwise fixed air bleed that allows air to bypass the throttle plate. ​ Screwing the BISS in //reduces// the amount of air that reaches the intake manifold, screwing the BISS out //​increases//​ the flow.  If the only problem is that the BISS needs to be adjusted, simply adjust the BISS until the ISCPosition value logged in DSMLink/​ECMLink hovers around 30 at normal warm-engine idle in neutral. ​ This produces better results than following the service-manual procedure. 
  
-You may find that screwing ​the BISS all the way in doesn'​t bring the idle speed down to idle speed configured in DSMLink/​ECMLink That means that some other path is allowing too much air to pass First make sure that there is no leakage into the BISS hole by covering ​the hole with your finger If the engine speed drops when you cover the holereplace ​the BISS O-ring.+The simplest path through ​the throttle body is the Basic Idle Speed Screw (BISS)This screw controls an otherwise fixed air bleed that allows ​air to bypass the throttle plateScrewing the BISS in //reduces// the amount of air that reaches the intake manifold, screwing ​the BISS out //​increases// ​the flow. If the only problem is that the BISS needs to be adjustedsimply adjust ​the BISS until the ISCPosition value logged in DSMLink/​ECMLink hovers around 30 at normal warm-engine idle in neutral. This produces better results than following the service-manual procedure.
  
-Next, investigate possible problems with the Idle Speed Control (ISC) servo. ​ Open the ECU and [[Driver01|inspect for burned ISC driver chips]]. ​ If you find any, [[http://​www.ecmtuning.com/​product/​servicerequest|contact ECMTuning regarding repair of the ECU]]. ​ If there //are// burned drivers, it's quite possible that the damage was caused by ISC itself having a shorted coil.  Make sure you are using the correct O-ring to seal the ISC to the throttle body. An O-ring that's too thin might not seal, too think and it might not allow the ISC to fully close the airway. 
  
-[[http://​www.youtube.com/​watch?​v=KibYz21IMA0|Test ​the coils in the ISC.]] (Note that the newer, more reliable, all-black ISCs normally measure about 39 ohms.)  Inspect ​the tip of the ISC for any physical damage.+You may find that screwing the BISS all the way in doesn'​t bring the idle speed down to idle speed configured in DSMLink/​ECMLinkThat means that some other path is allowing too much air to pass. First make sure that there is no leakage into the BISS hole by covering the hole with your fingerIf the engine speed drops when you cover the hole, replace the BISS O-ring.
  
-Test for proper operation of the ISC:  Turn off the ignition and reset the ECU by removing battery backup power for at least 10 seconds, then restoring battery backup. ​ Then, with the ISC unbolted from the throttle body but plugged in to the wiring harness, turn on the ignition and observe the movement of the ISC.  The ISC should fully extend, then retract slightly. ​ If the ISC just quivers a bit but doesn'​t really move, suspect a problem with the ISC, the driver circuits in the ECU, or the wiring. ​ If the ISC fully retracts instead of fully extending, there is a wiring problem, perhaps a mismatch between '90 and '91+ engine harness and ISC.  Using a '90 harness with a '91+ ISC, or vice versa, will cause the ISC to operate backwards. 
  
-Strange behavior can result from a bad Fast-Idle Air Valve This is a coolant-temperature controlled air valve that provides some of the additional air needed ​for fast idle during engine warm-up This valve is integral ​to the throttle body, so test by substitution or by blocking ​the FIAV passage with a block-off plate.+Next, investigate possible problems with the Idle Speed Control (ISC) servoOpen the ECU and [[:​driver01|inspect ​for burned ISC driver chips]]If you find any, [[http://​www.ecmtuning.com/​product/​servicerequest|contact ECMTuning regarding repair of the ECU]]. If there //are// burned drivers, it's quite possible that the damage was caused by ISC itself having a shorted coil. Make sure you are using the correct O-ring to seal the ISC to the throttle body. An O-ring that's too thin might not sealtoo thick and it might not allow the ISC to fully close the airway.
  
-With all other possibilities eliminated, the remaining item to check is the throttle plate. ​ A too-tight throttle cable can pull the thottle open, more so as the throttle-cable housing heats up, so make sure that the throttle cable has sufficient slack to allow the throttle to close to the stop even when the engine is hot.  Check that the throttle is against the stop by manually rotating the throttle shaft closed. ​ Make sure that nothing is binding the throttle shaft such as bad bearings or a badly adjusted throttle-position sensor. 
  
 +[[http://​www.youtube.com/​watch?​v=KibYz21IMA0|Test the coils in the ISC.]] (Note that the newer, more reliable, all-black ISCs normally measure about 39 ohms.) Inspect the tip of the ISC for any physical damage.
  
  
 +Test for proper operation of the ISC: Turn off the ignition and reset the ECU by removing battery backup power for at least 10 seconds, then restoring battery backup. Then, with the ISC unbolted from the throttle body but plugged in to the wiring harness, turn on the ignition and observe the movement of the ISC. The ISC should fully extend, then retract slightly. If the ISC just quivers a bit but doesn'​t really move, suspect a problem with the ISC, the driver circuits in the ECU, or the wiring. If the ISC fully retracts instead of fully extending, there is a wiring problem, perhaps a mismatch between '90 and '91+ engine harness and ISC. Using a '90 harness with a '91+ ISC, or vice versa, will cause the ISC to operate backwards.
  
 +
 +Strange behavior can result from a bad Fast-Idle Air Valve. This is a coolant-temperature controlled air valve that provides some of the additional air needed for fast idle during engine warm-up. This valve is integral to the throttle body, so test by substitution or by blocking the FIAV passage with a block-off plate.
 +
 +
 +With all other possibilities eliminated, the remaining item to check is the throttle plate. A too-tight throttle cable can pull the thottle open, more so as the throttle-cable housing heats up, so make sure that the throttle cable has sufficient slack to allow the throttle to close to the stop even when the engine is hot. Check that the throttle is against the stop by manually rotating the throttle shaft closed. Make sure that nothing is binding the throttle shaft such as bad bearings or a badly adjusted throttle-position sensor.
  
 ===== Other considerations ===== ===== Other considerations =====
idlesurge.txt ยท Last modified: 2016/01/12 18:41 by nickracer