Failed 3 E-Tests Volkswagen MK 2 Eratic Idling

I took my 1990 Volkswagen Golf Mk2 into get it E-tested today and this is the third 3rd time it failed. Have installed new oxygen sensor, new catalytic convertor, new plugs and changed the oil. The vehicle does have eratic idling at certain times and not all the time. One mechanic today suggested I change the Idle Stabilizer Valve. Would appreciate hearing from anyone who has experienced eratic idling and have them advise me what repair was necessary to fix it. Thanks Spar

Reply to
Spar
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Please post the results of the E-test (CO, HC, NOx, O2 etc.) as it is immensely useful in diagnosing an emissions problem. What type of fuel injection do you have? Digifant I, Digifant II? something else entirely?

A new ISV is expensive, don't change it unless you /know/ it is the problem. One common problem on A2 cars is that the idle switch on the throttle body fails (the one at the bottom that you can barely see, the one in plain view on top is the wide open throttle switch). This will cause erratic idle. Depending on what type of FI you have, you may or may not have an idle switch.

Reply to
Randolph

Why did it fail? Let's see the test results!

Reply to
Woodchuck

How? What doesn't measure up?

Oh yeah... there are lots of cheaper things to fix like the grommet between the head and the PCV valve; the probably-perished rubber vacuum tube joiners and lines around the throttle body.

Also check the dipstick tube; especially the plastic end where the dipstick is supposed to seat "air-tight".

And then making sure that the electrical connections to the cylinder head are good; both at the corner of the cam cover and at the side coolant flange.

Then there are other bits to check; like the coolant temperature sensor.

Mostly; a few drops of Stabilant 22A inside the air-flow meter; at the connector and on the carbon track.

You can also clean the ISV.

Reply to
Bernd Felsche

Judging from your email you're in Canada and probably have a Digifant II system.

The ISV can be cleaned out with carburetor cleaning solvent. Remove it from the car and spray the solvent into ever hole really good. This sometimes helps.

Also make sure that any and all vacuum lines are good and no leaks. Also check the PCV valve grommet on top of the valve cover and that the oil dipstick is seated properly. Any of those things, if leaking, will cause a vacuum leak and possible erratic idling. The coolant temperature sensor for the ECU also often goes bad (although usually the symptom of that is a rich high idle and not an erratic one) but it's a cheap thing to replace. As others have noted, the ISV is expensive and I've never heard of them going bad very often. There are other cheaper things to check first.

Reply to
Matt B.

As others have noted, it would help a lot if you posted what fuel injection your car is equipped with and what your emissions numbers are. They tell you all that stuff for a reason.

High NOx is usually an indication that the engine is running hot. This can be caused by a variety of things, including incorrect ignition timing, low octane fuel (lower than you need), faulty EGR valve (if equipped), or bad cat.

High CO is virtually always an indicator you are running rich.

High HC is an indicator you are burning something, either fuel or oil. If your CO levels are low, it probably means you are burning oil, if your CO levels are high its probably running rich.

A faulty catalytic converter can affect all three readings, however catalytic converters generally speaking are only effective if the car is running relatively cleanly to begin with, so if you have a high CO reading, the cat would be the last thing I'd check and the O2 sensor and the coolant temperature sensors would be the first. The coolant temperature sensor is just a thermistor and can be checked easily with a multimeter.

I hear a lot of people complaining of erratic idle and the first thing they want to do is replace the idle stabalizer valve. I personally have rarely seen one fail. They can be cleaned with carburetor or fuel injection cleaner as others have mentioned, but I'm not even convinced thats that much help. The first thing to do is to simply unplug the idle stabalizer valve and see what happens. One thing that most people don't realize is that a PROPERLY functioning idle stabalizer valve can turn what seems like a minor idle problem into a major one because of its nature as an active feedback system.

An erratic idle (and nothing else) is usually caused by an air leak. Common places are in anything rubber, around hose clamps (make sure they are tight), vacuum lines, particularly rubber ones or the rubber joints, and around the fuel injectors. If you have CIS based injection it might behoove you to pull out the injectors and injector inserts and replace the lower insert and all the seals (2 on the injector one on the lower insert). As someone else suggested, it's probably a good idea to check the WOT and idle switches. One generally good thing to try is to start the car, and then push/squeeze/twist/pump anything that is flexible. This should have virtually no impact on the idle quality. If it does you found a problem, look for rips, tears, or loose connections.

dan

Reply to
dan

Like others have said..............check the idle and WOT switches. I will assume that you have the Digifant II system, but I am not sure on this. If you do you might find a wiring problem at the intake manifold or cylinder head (ground wire breaks) Or maybe a defective Fuel Pressure Regulator.

IF CIS-x, it might be a wiring issue (again ground) at the cold start valve.

Just to give you more things to check. DON'T JUST THROW PARTS AT IT!!! Check it out with a digital Volt Ohm Meter and a good book (Bentley). ;-)

Reply to
dave AKA vwdoc1

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