Information on diagnostics

Intake manifold pressure error at idle

Troubleshooting in vehicles with MAP sensors

Fluctuating idle speed? Engine jerking on acceleration? Diagnostic trouble code P0105, P0106, P0107, P0108 or P0109 in the fault code memory? This suggests a problem with the intake manifold pressure, but the cause is not always to be found in the MAP sensor (intake manifold pressure sensor). Click here for a handy checklist to use when troubleshooting engine issues.

Potential complaints

  • Fluctuating idle speed
  • Loss of power
  • Jerking on acceleration
  • Malfunction indicator lamp lights up
  • Diagnostic trouble code P0105 – P0109

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

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