1500 rpm fast idle IAC drops to Zero, TPS is at .42 cannot lower idle?? HELP!!!

[robg8678]

Ok, car ran great, installed the intake plate and then the high idle problem occured, removed plate and the same problem, checked all gaskets and cannot find any vaccumm leak anywhere on the vehicle. When the engine warms up it will idle up to 1500rpm, and the iac drops to zero and I checked and it is fully closed. adjusted the air bleed srew all the way and the iac remains at zero. This would tell me that there is a vaccumm leak, but I have checked 5 times. Fuel trims seem to remain pretty close to 128, iac has been replaced. Any help would be great... Thanks

 

[Iceman]

It has to be sucking air some where around the top intake.Check all the lines and can you here it sucking air?

 

[robg8678]

There is no sucking noise that can be heard, I sprayed everything with starting fliud, no idle change. One other strange thing is when I jump the ALDL connector, I am assuning this fully closes the iac, I can set the base idle at 550-650 rpm... Thanks

 

[GN owner]

Does your scantool see the ECM in the ALDL mode or is it in normal mode? In the diagnostic mode the idle is turned up by the ECM. Maybe somehow your ECM might be in the diagnostic mode?

 

[robg8678]

Not sure what you mean? open/closed loop? It will go into closed loop normally, not running rich or lean?

 

[GN owner]

I use Turbo Link and sometimes the ECM somehow goes into ALDL mode instead of NORMAL. When this happens I notice the idle speed increases up to 1000+ RPMs. According to the T-Link manual it states, "The Assembly Line Diagnostic Link (ALDL) mode allows you to read different data from the ECM. This mode is sometimes referred to as the "Special State" or the "10K Ohm State" in some repair manuals. Fuel injected GM vehicles automatically raise the idle speed to 1000 RPM and add extra spark advance to the spark calculations when in the mode. The ALDL mode feature is primarily used to check the operation of the Electronic Spark Control (ESC)."

Just thought this might be your case as I have experienced this on my car.