Table of contents: TO #7 ↓ Verification conditions ↓ Exhaust gas analysis ↓ The CO indicator differs from the… ↓
TO #7
6-cylinder engines are equipped with automatic regulation of the engine speed in idle mode. There is no adjustment bolt - so there is nothing to adjust. The speed in idle mode is simply checked. Under the correct testing conditions (more on that below) the following rotation speed indicator should be set: 680-820 rpm (2.6 liter engine) or 700-800 rpm (2.8 liter engine). Otherwise:
Check all elements of the intake system (pipeline, sealing gaskets) for leaks. Penetrating unaccounted air can change the idle speed so much that even the idle speed stabilization valve cannot compensate for it.
Interrogate the fault memory at the workshop. There may be another fault.
Verification conditions
The conditions for checking the idle speed are the engine temperature warmed up to operating temperature, as well as serviceable injection and ignition systems.
Next, you need to turn off all electrical consumers in the car.
The cooling fan should also not work.
Remove both crankcase ventilation pipes and plug the ends of the hoses.
Turn off the air conditioner.
Set the automatic transmission shift lever to the "N" or "P" position.
Warm up the engine to operating temperature (oil temperature at least 60°C).
The replacement air filter element must be in a perfectly clean condition.
For CO analysis, no exhaust device should be connected to the exhaust system.
Exhaust gas analysis
At home, CO content testing is usually not carried out, since this procedure is mandatory during the annual technical inspection. In addition, a special device is needed for this. The description of the work performed is checked only after the injection system is brought to the so-called basic position using the VAG 1551 fault memory reader. What does it mean to disable certain adjustment functions (for example, lambda regulation) to obtain reasonable comparable values.
Connect the exhaust gas toxicity measuring device to the right measuring tube at the front of the engine compartment. Ensure a tight fit.
Start the engine and let it idle.
The measuring device should show 0.15-1.0% CO (2.6 liter engine) or 0.3-1.2% CO (2.8 liter engine).
On models with a 2.8-liter engine, the CO content can be adjusted using the adjusting screw on the air flow meter.
With a 2.6-liter engine, there is no possibility of regulation. If the measurement showed a different CO content, it is necessary to look for the cause using the fault memory.
The CO indicator differs from the standard
If the CO values differ, it is necessary to look for leaks in the air supply and exhaust system (a faulty spark plug increases the CO content by 1.5%).
CO level too high:
- Check the injection nozzles
- Fuel pressure too high
- The temperature sensor is faulty
CO level too low:
- Unaccounted air enters the air supply system
Note: Everything you need to know about CO testing, catalytic converter operation testing, lambda probe testing, you will find in the chapter "Mono-Motronic injection system". When troubleshooting, the lambda probe is checked using the method, described here.
Disconnecting the battery erases the idle speed correction factor of the injection system. Therefore, the system must slowly re-adjust to the correct speed, a process that takes several minutes. So do not panic right away if the car suddenly does not run perfectly after replacing the battery, just drive a little until the adjustment is complete.