More analysis on Low RPM Hesitation
09-26-2008, 12:46 PM
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More analysis on Low RPM Hesitation
I finally read the instructions!
In the repair manual under trouble shooting, ther is a expalanation on how to use the CEL for diagnosis.
1) Turn the key on but don't start the car. Push and hold the accelorator for three seconds and slowly let up.
2) If there is a fault code you will get a series of flashing CELs. These flashes translate to the error codes in the manual.
3) My error code is the O2 Sensor is faulty. The manual further states that if the 02 sensor is bad, the car goes into "No sensor" mode and shuts it out of the system. Interestingly, I changed my 02 sensor first in my quest and it did not change anything. I'm wondering if the system has kept the fault code in or that I may have gotten a bad 02 sensor.
There is also a test process for the 02 sensor. I will test it when i get home with the voltmeter as they recommend.
In the repair manual under trouble shooting, ther is a expalanation on how to use the CEL for diagnosis.
1) Turn the key on but don't start the car. Push and hold the accelorator for three seconds and slowly let up.
2) If there is a fault code you will get a series of flashing CELs. These flashes translate to the error codes in the manual.
3) My error code is the O2 Sensor is faulty. The manual further states that if the 02 sensor is bad, the car goes into "No sensor" mode and shuts it out of the system. Interestingly, I changed my 02 sensor first in my quest and it did not change anything. I'm wondering if the system has kept the fault code in or that I may have gotten a bad 02 sensor.
There is also a test process for the 02 sensor. I will test it when i get home with the voltmeter as they recommend.
09-27-2008, 11:49 AM
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If your CEL stays on all of the time and you get an O2 code then the O2 sensor or circuit failed. If you are in "limp home" the CEL will stay on.
If the CEL is not on all of the time you have a stored code which may mean nothing. Clear the codes and check it again.
A weak or bad O2 will not cause a hesitation. However, if the CEL is always on all bets are off.
My post in the "Idle control valve" thread:
--------------------------------------------------------------------------------
Just suggestions here, as I can't diagnose from my keyboard.
If your car doesn't lose power under heavy acceleration then your fuel pressure should be fine. I've never seen a fuel pump cause an off idle hesitatiion. Could be a first though.
Your plugs are white or light gray in color because of the additives that you have used.
Never clean a MAF.
Causes that are most likely, but not limited to:
Bad MAF- try tapping on it lightly as the car idles to see of there is a dip in RPM.
- Bosch makes a very good MAF though. You can also diagnose it by disconnecting it and driving the car. Some cars will run this way in a "limp home" mode. Others won't run at all. But you can try.
Cracked/loose air tube between MAF and throttle body. When the engine torques it can open up a split in the tube or pull any additional additonal hoses loose. Then when the engine smooths it's fine again. Also be sure that the clamps are centered and tight. A skewed clamp is a problem.
Dirty throttle plate. Check top, bottom and the back of the plate. Clean only with air intake cleaner. Using other stuff such as CRC, brake or carb cleaner will kill your O2 sensor. Don't spray a whole can in there either. Small sprays and a clean lint free cloth. Be sure there is no play in the throttle shaft. Just wiggle the linkage. While your there have someone hold the gas to the floor to see if the plate opens 100%. I've had three 951s and they all would only open about 85 to 90 percent.
Vacuum leaks. How much vacuum are you pulling at idle?
Misadjusted idle speed.
I don't know if the TPS on these cars are adjustable... If it is and it's misadjusted the computer won't know when to increase the injector pulse width when the throttle is off idle. This is also why you should never screw with your idle speed unless you use the proper method.....
Fun stuff.
, Bill
If the CEL is not on all of the time you have a stored code which may mean nothing. Clear the codes and check it again.
A weak or bad O2 will not cause a hesitation. However, if the CEL is always on all bets are off.
My post in the "Idle control valve" thread:
--------------------------------------------------------------------------------
Just suggestions here, as I can't diagnose from my keyboard.
If your car doesn't lose power under heavy acceleration then your fuel pressure should be fine. I've never seen a fuel pump cause an off idle hesitatiion. Could be a first though.
Your plugs are white or light gray in color because of the additives that you have used.
Never clean a MAF.
Causes that are most likely, but not limited to:
Bad MAF- try tapping on it lightly as the car idles to see of there is a dip in RPM.
- Bosch makes a very good MAF though. You can also diagnose it by disconnecting it and driving the car. Some cars will run this way in a "limp home" mode. Others won't run at all. But you can try.
Cracked/loose air tube between MAF and throttle body. When the engine torques it can open up a split in the tube or pull any additional additonal hoses loose. Then when the engine smooths it's fine again. Also be sure that the clamps are centered and tight. A skewed clamp is a problem.
Dirty throttle plate. Check top, bottom and the back of the plate. Clean only with air intake cleaner. Using other stuff such as CRC, brake or carb cleaner will kill your O2 sensor. Don't spray a whole can in there either. Small sprays and a clean lint free cloth. Be sure there is no play in the throttle shaft. Just wiggle the linkage. While your there have someone hold the gas to the floor to see if the plate opens 100%. I've had three 951s and they all would only open about 85 to 90 percent.
Vacuum leaks. How much vacuum are you pulling at idle?
Misadjusted idle speed.
I don't know if the TPS on these cars are adjustable... If it is and it's misadjusted the computer won't know when to increase the injector pulse width when the throttle is off idle. This is also why you should never screw with your idle speed unless you use the proper method.....
Fun stuff.
, Bill
