Engine (Audi 100 C3)

Engine does not turn over when starting

• The battery terminals are loose or corroded ("Weekly checks").
• Discharged or defective battery (Section 4A).
• The wiring in the starter circuit is broken or disconnected (Section 4A).
• Defective starter traction relay or switch (Section 4A).
• Defective starter (Section 4A).
• The starter gear or flywheel ring gear teeth are defective (Section 1).
• The engine ground strap is broken or disconnected (Section 4A).

The engine turns over but does not start

• The fuel tank is empty.
• The battery is discharged (the engine is turning slowly) (Section 4A).
• The battery terminals are loose or corroded.
• Defective pre-heating system - diesel models (Section 4B).
• Fuel shut-off valve not working - diesel models (Section FOR).
• Air in the Fuel System - Diesel Models (Section 3A).
• Serious mechanical failure (for example, camshaft drive)

Difficulty starting a cold engine

• Discharged battery (Section 4A).
• Battery terminals are loose or corroded
• Defective pre-heating system - diesel models
• High idle speed valve not adjusted correctly - diesel models.
• Low compression in engine cylinders (Section 1).

Excessive noise in the starter when turned on

• The starter gears or flywheel ring teeth are damaged (Sections 1 and 4A).
• Starter mounting bolts are loose or missing (Section 4A).
• The internal components of the starter are worn or damaged (Section 4A).

Unstable engine idle speed

• The air filter element is clogged.
• Uneven or low compression in engine cylinders (Section 1).
• The camshaft cams are worn out (Section 1).
• Incorrect tension of the timing belt.
• Defective injector - diesel models (Section FOR).

Misfires at idle speed

• Defective injector - diesel models (Section FOR).
• Different or low compression in engine cylinders (Section 1).
• Disconnected, leaking or kinked crankcase ventilation hoses (Section ZV).

Misfires at all engine speeds

• The fuel filter is clogged.
• Defective injector - diesel models (Section FOR).
• Uneven or low compression in engine cylinders (Section 1).
• Fuel system damage (Section FOR).

Engine shakes when accelerating

• Defective injector - diesel models (Section FOR).

The engine stalls

• The fuel filter is clogged.
• Defective injector - diesel models (Section FOR).

The engine does not develop power

• Incorrect tension of the timing belt (Section 1).
• The fuel filter is clogged.
• Uneven or low compression in engine cylinders (Section 1).
• Fuel system damage (Section FOR).
• Defective injector - diesel models (Section FOR).
• Fuel pump faulty - diesel models (Section FOR).
• Brakes sticking (Section 9).
• Clutch slippage (Section 5).

The oil pressure warning light is on

• Low oil level or wrong type of oil ("Weekly checks").
• Defective oil pressure sensor (Section 4A).
• The engine bearings and/or oil pump are worn out (Section 1).
• High engine operating temperature (Section 2).
• The oil pump bypass valve is faulty (Section 1).
• The mesh filter of the oil intake tube is clogged (Section 1).

The engine continues to run after being turned off

• Excessive increase in carbon content in the engine (Section 1).
• High engine operating temperature (Section 2).
• The fuel shut-off valve on the pump is faulty - diesel models (Section FOR).

Whistling or wheezing noises from the engine

• Leaking exhaust manifold gasket or downpipe coupling
• The cylinder head gasket is broken (Section 1).

Fluid leaking and rattling noises

• The valve mechanism or camshaft is worn out (Section 1).
• Damage to auxiliary components (water pump, generator, etc.)

Detonation or dull noises

• The lower connecting rod head bearings are worn out (regular heavy detonation, possibly less under load) (Section 1).
• The main bearings are worn out (rumble and detonation, worsening under load)
• Piston wear (especially noticeable on a cold engine) (Section 1).