Possible causes of the malfunction:
- decrease in fuel pressure in the power system (see «Checking the pressure in the power system»);
- air filter resistance increase (see «Replacing the air filter element»);
- nozzle contamination (see «Removing, checking and installing injectors»);
- soot on spark plugs (see «Diagnostics of the engine condition by the appearance of spark plugs»);
- coking of the exhaust system or damage to the exhaust gas converter.
Often, a decrease in engine power and its unstable idling are due to a failure of the throttle position sensor installed in the throttle assembly cover...
... by contamination of the damper itself (places of deposition of pollution are shown by arrows) or suction of foreign air through loose hose connections attached to the intake pipe. If cleaning the throttle body or tightening the hose clamps fails to restore idling, contact a specialist to check the throttle position sensor or replace the throttle assembly. «Removal and installation of the throttle assembly»).
NOTE: In addition to the main causes listed above, the engine may start poorly and run erratically if the canister purge valve is malfunctioning or if air is sucked through the evaporative emission system hose connections.
If checking all of the listed elements did not work, check the compression in each of the cylinders (see «Cylinder compression check»). Normal compression is more than 1.0 MPa, a difference of more than 0.1 MPa in one cylinder indicates the need for engine repair.