Troubleshooting / common fixes

This topic comes up again and again on forums… Posts typically are called “cutting out”, “no tick over” or the most useful type “car problems, HELP”.

So here are my basic steps to troubleshoot a Golf MK3. I’ve not worked on the VR6 or the diesel’s, so these steps are about the 1.8 GL and 2l GTI mostly – but applicable to the 1.4 and the 1.6. These basic steps are the first things to check, and the most likely things to be wrong before delving into expensive parts changes, or diagnostics. No harm is done by doing the basic steps, nor are they particularly expensive.

These basic steps are suitable for the reasonably competant car DIY’er. If you’re not comfortable doing them – then DONT! I’d always suggest a Haynes or Bentley’s workshop manual for reference!

Disclaimer: I am not a mechanic!! This is the result of my knowledge from a few courses, a lot of reading and some trial and error!

The Basics….;

1) Is an error light on the dash lit? Oil pressure light? If so resolve these problems first. Get the codes read – VAG (VCDS) com for the VW’s – might indicate an area to start looking at. More often than not on the older cars (aka mk3′s) – no codes stored!

2) Sparkplugs. Look on NGK’s websites for your model – order from the web, or Halfords…
Symptoms: Misfiring (engine sounds like a tractor), misfire at low rev’s, bad engine pickup, bad fuel consumption, etc. Change them with the engine COLD (or you can strip out the plug seats from a hot head), and fit the new ones by hand first before tighting so you don’t cross thread them! NGK parts finder

3) HT leads.
Symptoms: as above. VW’s are silly expensive (£20 per lead… 5 required!) – best non OE (Original Manufacturer) parts are sold from GSF Car Parts. Part number is “92631F” desc “IGNITION LEAD SET-BQ G3 1.6/1.8/2.0 GTI 8V”.

4) Distributor cap & arm.
Symptoms: as above again – all related. Go to VW and get the parts, not expensive. When you change them be careful to put the leads back in the same order(do it one at a time), and be extremely careful to put the arm and cap back in exactly the same place. Consult a workshop manual for detailed references here!

5) Air filter. Check and change if required.
Symptoms: slugglish engine, and poor MPG

6) Oil Breather pipes. Check that the pipes from the engine block to the air intake are clear. You can just take them off and check them. Check them for splits and cracks too.
Symptoms: Can cause stalling and rough running.

7) Throttle body clean. The throttle body’s can get gunked up – enough to stop the car idle’ing due to lack of air flow when the throttle butterfly is closed. Get some carb cleaner and a toothbrush….
Quoting RubJonny here who explains it well – The later AGG/ADY doesnt have one [ISV], instead the idle is regulated by a stepper motor in the throttle body. this is why on the later cars a dirty throttle body causes issues, the stepper motor puts the car into ‘idle’ position, but its all blocked up with crud so the expected amount of air cant get past, so stall.
Symtoms: Bad idle, stalling at idle

8 ) “Vacuum” Hoses… The later model Golfs use an air-flow-meter, also called MAF or AMM (air-mass-meter), to measure the incoming air volume. If there are air leaks after the sensor, the engine will not be happy. Disconnect the pipes carefully and check for holes/splits/wear etc.
Symptoms: stalling, misfiring, general poor running and poor MPG

9) Battery, connections… Check all the connectors are connected, no visable damage. Check the battery voltage (> 12.5v engine off) and terminals are tight.
Symptoms: Hard starting, cutting out, general gremlins.

10) Oil & filter change. No direct benefit, but keeps the engine in good working order, cool, etc.

Intermediate steps…

OK so you’ve done the basics… And it still doesn’t work…

11) Relays… The ECU and Fuel pump relay are known issues with the mk3′s. Both can cause running issues / cutting out issues. ECU is relay no. 30 and the Fuel pump is no. 167. Check the parts page on this site for the VW part numbers.

12) Coolant temp sensor… Easy to change and cause of engine running rich problems. Symptoms are engine that doesn’t idle happily, runs lumply but when driven hard performs well. Couple of different places they are located: on the 8v’s – in the top hose at the front of the engine going to the radiator, for the 16v’s to the right in the coolant hoses there.

13) Grounds. Start the car and turn everything on – lights, heaters, fans etc. Measure the voltage between the engine block and the battery negative terminal. Should be below 0.5v. Switch the engine off before changing anything. Check the three grounds on the front of the engine block – should be clean and tidy. Check the main ground cable from the negative post to the engine block and chassis.

14) Thermostat. Can be related to (12) in that a stuck thermostat can show as an engine that doesn’t come up to temperature. For reference the Golf should warmup to 90 degrees (C) within 10mins of reasonable driving – summer or winter… Should never stay below 90 for long. Worth doing both temp sensor and t’stat whilst your there – as underheating or overheating could be either.

15) Ignition Coil. These don’t often die, but obviously they can.
Symptoms; the engine will cut out and/or start misfiring badly, or lack power at low RPM. A failing coil can show up as an ignition issues – see steps 2-4 above. Before changing check the primary and secondary resistances, and the supply coil voltage and grounds.

16) Airflow meter – if you have one – i’ll be on the airbox pipe between the airbox and the intake manifold. Typically Bosch, Siemens or Hitachi if memory serves. An interesting test is to remove it and spray the two sensor wires inside liberally with electrical contact cleaner. Let it dry then refit. If problem improves, then replace the sensor. VW calls these Air Mass Meter (AMM’s) and they are an exchange part. Other name for the part is a MAF (Mass Air Flow meter). Can be tested with a o’scope too – but I found it difficult to see subtle problems. Try this too.

Symptoms: Rough running, can cause loss of power at idle or lumpness at low revs and loss of power at high RPM depending on fault.

Advanced steps….

Final stuff – best in conjuction with a reputable garage, as these steps can cause issues not performed correctly. Also, if there are major engine faults then you’ll probably need a garage to resolve it for you anyway. As always consult a workshop manual first!

17) Crank/Cam sensors. These tell the ECU where the engine is – and give it the timing for injection and ignition. The wires get brittle over time and with the crank sensor the wires can get burn’t away with oil & engine temp. (see Here. To check the cam – check the wiring from the dizzy. For the Crank get a torch and look behind the oil filter and see if you can see the sensor and the wiring. Issues: Cutting out, lumpy power at low rev’s, poor MPG etc.

18) Ignition timing. On the mk3′s this is checked with the engine off – i.e. static timing. Essentially you are checking that with the engine in TDC that the distributor is pointing at the correct place. This allows the engine to vary the timing as it warms up and is under load. You don’t need a timing light!!! See steps 17 and 18 from this. But don’t take your car apart – as he’s changing his water pump and timing belt! All you need to do is: Lift the drivers side front wheel off, take the top cambelt cover off and turn the wheel with the engine off but in gear until it lines up as shown. Check the green plug hole in the gearbox for the crank maker and then check the dizzy possition as shown. Re-assmbly is reverse of taking it apart!

19) Lamda sensor. Ditto above, but testable on a multimeter. Worth checking the heater element is working too. Common issues as above. A set of crows-feet is very useful for changing the sensor!

20) Compression test. Easy to do and will show any serious mechanical problems within the engine – i.e. piston rings, valve damage, head gasket, bad (mechanical as apposed to ignition) timing.

21) Oil pressure test. Won’t fix anything unless you have the low oil pressure light on – which could also be the sensor. But if your in this stage, worth checking you have oil pressure!

Thanks for reading…

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