High Idle...is this normal?
Thread Starter
Registered User
Joined: Dec 2005
Posts: 343
From: Orlando, FL
High Idle...is this normal?
At times my car (m6) will idle at 1500 rpms for pretty long periods of time.
On initial startup itll just sit there pegged at 1500 and then even when I drive it'll continue to be at 1500.
Sometimes it'll return to normal and idle at like 800-1000, other times it will continue to stay at 1500 even when the engine is warm.
Is this normal?
On initial startup itll just sit there pegged at 1500 and then even when I drive it'll continue to be at 1500.
Sometimes it'll return to normal and idle at like 800-1000, other times it will continue to stay at 1500 even when the engine is warm.
Is this normal?
Administrator
Joined: Nov 1998
Posts: 71,086
From: Hell was full so they sent me to NJ
Not normal. Idle speed is increased only when coolant temps are low. And it never sets the idle at 1,500rpm. The stock programming for an M6 is:
COOLANT
TEMP
deg F
-40*F: 1,200rpm
-19*F: 1,050rpm
+3*F: 1,050rpm
+24*F: 1,000rpm
+46*F: 900rpm
+68*F: 900
+89*F: 900
+111*F and above: 800rpm
Remember that the stock tach typically reads 100-200rpm higher than actual rpm. Better to read rpm off a scanner, direct from the PCM.
In any case, unless your coolant temp sensor is faulty (which would cause other problems, like preventing the PCM from entering closed loop), there is no reason for the engine to idle at 1,500rpm at any time.
You might also want to check the throttle position sensor (TPS). If its reading above 0.90V at closed throttle, it can cause the PCM to hold higher idle speed. But that should also set a code.
Have you verified that the throttle blades and cable are moving freely, and that the blades are closing fully at idle, all the time?
Have you checked for vacuum leaks? Again, a scanner can help you, because you can watch how the IAC counts respond to the higher than programmed idle speed. Possibly the counts are bottomed out at "0" and the IAC motor can't control the idle.
Hve you checked for a tear in the inlet elbow, or the bottom edge being folded under and not on the throttle body?
COOLANT
TEMP
deg F
-40*F: 1,200rpm
-19*F: 1,050rpm
+3*F: 1,050rpm
+24*F: 1,000rpm
+46*F: 900rpm
+68*F: 900
+89*F: 900
+111*F and above: 800rpm
Remember that the stock tach typically reads 100-200rpm higher than actual rpm. Better to read rpm off a scanner, direct from the PCM.
In any case, unless your coolant temp sensor is faulty (which would cause other problems, like preventing the PCM from entering closed loop), there is no reason for the engine to idle at 1,500rpm at any time.
You might also want to check the throttle position sensor (TPS). If its reading above 0.90V at closed throttle, it can cause the PCM to hold higher idle speed. But that should also set a code.
Have you verified that the throttle blades and cable are moving freely, and that the blades are closing fully at idle, all the time?
Have you checked for vacuum leaks? Again, a scanner can help you, because you can watch how the IAC counts respond to the higher than programmed idle speed. Possibly the counts are bottomed out at "0" and the IAC motor can't control the idle.
Hve you checked for a tear in the inlet elbow, or the bottom edge being folded under and not on the throttle body?
Thread Starter
Registered User
Joined: Dec 2005
Posts: 343
From: Orlando, FL
Not normal. Idle speed is increased only when coolant temps are low. And it never sets the idle at 1,500rpm. The stock programming for an M6 is:
COOLANT
TEMP
deg F
-40*F: 1,200rpm
-19*F: 1,050rpm
+3*F: 1,050rpm
+24*F: 1,000rpm
+46*F: 900rpm
+68*F: 900
+89*F: 900
+111*F and above: 800rpm
Remember that the stock tach typically reads 100-200rpm higher than actual rpm. Better to read rpm off a scanner, direct from the PCM.
In any case, unless your coolant temp sensor is faulty (which would cause other problems, like preventing the PCM from entering closed loop), there is no reason for the engine to idle at 1,500rpm at any time.
You might also want to check the throttle position sensor (TPS). If its reading above 0.90V at closed throttle, it can cause the PCM to hold higher idle speed. But that should also set a code.
Have you verified that the throttle blades and cable are moving freely, and that the blades are closing fully at idle, all the time?
Have you checked for vacuum leaks? Again, a scanner can help you, because you can watch how the IAC counts respond to the higher than programmed idle speed. Possibly the counts are bottomed out at "0" and the IAC motor can't control the idle.
Hve you checked for a tear in the inlet elbow, or the bottom edge being folded under and not on the throttle body?
COOLANT
TEMP
deg F
-40*F: 1,200rpm
-19*F: 1,050rpm
+3*F: 1,050rpm
+24*F: 1,000rpm
+46*F: 900rpm
+68*F: 900
+89*F: 900
+111*F and above: 800rpm
Remember that the stock tach typically reads 100-200rpm higher than actual rpm. Better to read rpm off a scanner, direct from the PCM.
In any case, unless your coolant temp sensor is faulty (which would cause other problems, like preventing the PCM from entering closed loop), there is no reason for the engine to idle at 1,500rpm at any time.
You might also want to check the throttle position sensor (TPS). If its reading above 0.90V at closed throttle, it can cause the PCM to hold higher idle speed. But that should also set a code.
Have you verified that the throttle blades and cable are moving freely, and that the blades are closing fully at idle, all the time?
Have you checked for vacuum leaks? Again, a scanner can help you, because you can watch how the IAC counts respond to the higher than programmed idle speed. Possibly the counts are bottomed out at "0" and the IAC motor can't control the idle.
Hve you checked for a tear in the inlet elbow, or the bottom edge being folded under and not on the throttle body?
And I haven't checked real recently, but I did have to fix that at one point as the elbow edge was folded back on the throttle body.
Administrator
Joined: Nov 1998
Posts: 71,086
From: Hell was full so they sent me to NJ
You can use a hardware scanner like the ones made by Auto-Xray or Actron (not the $30 shorts-the-pins code reader), or get software for a laptop from Freescan (free download and use), TTS DataMaster (free download and 20 uses), EFILive V4 (costs) or pcmcomm bundled with LT1_Edit. Get a cable from AKM Electronics.
The "problem" with your 95 is the fact that it has an OBD-I PCM and an OBD-II ALDL connector under the dash. AKM makes a cable specifially for the 95. Auto-Xray has an adapter plug for their OBD-I scanner. Or, if you have the full OBD-I cable, Shoebox has a photo showing how to jumper the 12-pin OBD-I cable pins to the 16-pin OD-II ALDL connector.
I have an online guide to reading scan data for the LT1:
http://members.aol.com/InjuneerZZ/ScanMast.htm
The "problem" with your 95 is the fact that it has an OBD-I PCM and an OBD-II ALDL connector under the dash. AKM makes a cable specifially for the 95. Auto-Xray has an adapter plug for their OBD-I scanner. Or, if you have the full OBD-I cable, Shoebox has a photo showing how to jumper the 12-pin OBD-I cable pins to the 16-pin OD-II ALDL connector.
I have an online guide to reading scan data for the LT1:
http://members.aol.com/InjuneerZZ/ScanMast.htm
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