Situation
Error messages relating to the intake manifold pressure often appear in petrol engines that have intake manifold pressure measurement via a MAP sensor (MAP = Manifold Air Pressure).
Deviation from the set-point values does not, however, lead to the diagnostic trouble code being stored in all operating states.
Determining the source
A scan tool can be used to compare the actual values with the set point values. If the intake manifold pressure measured by the system deviates from the set-point value, the actual value must be checked using a separate vacuum manometer.
- If the measured intake manifold pressure is within the set-point values, the MAP sensor and the electrical lines must be checked.
- If the measured intake manifold pressure is outside of the set-point values, the reason for the loss of pressure in the engine must be established (see test instruction that follows).
Potential complaints
- Fluctuating idle speed
- Loss of power
- Jerking on acceleration
- Malfunction indicator lamp lights up
- Diagnostic trouble code P0105 – P0109
Possible fault sources in the engine periphery
- Leaking intake manifolds downstream of the throttle valve (e.g. due to defective intake manifold gaskets, hoses, etc.)
- Defective engine exhaust valves/hoses
- Leaking brake boosters
- Leakages in the vacuum system (e.g. vacuum-operated actuators, brake boosters, lines, etc.)
- Defective EGR valves (permanently open)
- Defective idling actuators
- Idling status of the engine is not recognised by the control unit (defective throttle potentiometer, throttle switch)
- Defective or dirty throttle valves
- Incorrect or faulty air fi lter inserts
- Carbon deposits or other blockages in the intake manifold
If the problem is not found in the engine periphery, it must be assumed that there is a mechanical problem with the engine.
Possible fault sources in the engine mechanics
- Piston ring wear or piston damage (piston seizure, fusion and and similar damage) – a further sign of this is high blow-by gas emission during idling with the oil fi ller cap open.
- Leaking intake and exhaust valves
- Insuffi cient valve clearance
- Worn valve seat inserts (especially in engines with gas conversion)
- Incorrect function of the hydraulic valve clearance compensating elements (hydraulic tappet)
- Incorrectly set valve timing or skipped toothed belt
- Leaking cylinder head gaskets
- Incorrect or worn camshafts
Inspections to be carried out
- Valve clearance
- Valve timing check
- Compression test
- Cylinder compression test