MK3 VW -- injection problem, help!

So I've got a 1995 VW Jetta. It's the OBD-I, ABA motor (2l, 4 cyl.) Runs like E36M3, and I don't mean that in the good way.

Runs rich, especially at startup and low-speed running; almost feels like it's fouling the plugs. Get low-20s MPG in town, high-20s on the highway. So, yeah -- something is dumping waaaay too much fuel in there.

Have done a tuneup -- didn't improve anything, but at least I know that coil, wires, plugs, AF are all good; throttle body and AFM are cleaner than they used to be.

I did the code-blink thing, and got a ton of different codes -- most of which, it looks like, VWs throw just for fun. The one that looks like a real data point also appears to be a catch-all code:

2231 Idle-speed stabilizer adjustment limits exceeded; too-fast idle. Adjust throttle for full closing, check for vacuum leak, check ignition timing. Or Air Mass Sensor - Check sensor and wiring.

I've checked for a vac. leak, and the wiring for the MAF seems to be all right -- tested with a volt meter. MAF signal seems, based on my half-assed testing, to change very slowly. Seems to match the book value at idle, though.

So -- does it sound like the MAF is bad? Can it be cleaned up & made better, or is it dead?

Any suggestions for other things to test/check?

TIA. Matt

o2 sensor perhaps... Check with a meter, see it it swings between .1 and .9 volts back and forth constanly.

later, matt

xFactor wrote: o2 sensor perhaps... Check with a meter, see it it swings between .1 and .9 volts back and forth constanly. later, matt

Uhh...

would that be a good thing, or a bad thing?

You know how they say "there are no dumb questions"? Well, when I start messing with fuel injection, we get close.

Matt

That's a good thing if things are fine.

Let's say you really have a vacuum leak and a good o2. The o2 should be pegged out at 1volt all the time, showing the ecu it's rich, which can't compensate if it's a big leak, and eventually throw codes.

If the o2 is borked it usually reads low, less than .3volts constantly, sending a lean reading to the ecu, which tries to adjust by fattening up the mixture, to no avail, and eventually throw codes too.

When things are good, the o2 and the ecu keep swerving back and forth between rich and lean, keeping things at a happy medium.

How many miles? Later, Matt

Most likely suspects are MAF, O2, and coolant temp sensor.

Coolant temp sensor, MAF then O2. I would attack in that order.

I had a few spare minutes yesterday, so I opened the hood to look for the connector where I could read the O2 sensor voltage -- it's down at the bottom of the firewall, mostly hidden by the manifolds.

While I was in there poking around, I noticed that the bottom bolt on the MAF was oily... and there was oil on the rubber intake hose.

So I took the MAF off, and there was of course a bunch of oil inside it. Cleaned it, and put it back on -- because I was out of time at that point. Car drove a lot nicer. It had been maybe 15,000 miles since I cleaned the MAF. FWIW, looks like the idle compensator is full of oil, too.

Today, back to the same old. Now, I didn't clean all the oil out of the intake tract, didn't wash the air filter, which I'm sure is full of oil, too. This wasn't a fix, so much as a proof of concept.

So I'm pretty sure that the problem is related to the MAF getting covered in oil. Now, the reason for that... not so sure.

Apparently some later ABA motors had a more complicated PCV setup, with a heater and a vacuum shutoff, to keep from putting so much liquid oil into the intake. Mine doesn't have this, just a plain-Jane PCV dumping into the intake.

I can see three basic options: 1. replace PCV (on the theory that the problem is just a bad PCV) 2. replace PCV with fancy later setup (problem=bad PCV design?) 3. replace PCV with catch-can (problem=blowby?)

The car uses about a quart in 3,000 miles, and has 140,000 on it. Thoughts? And thanks for getting me this far. Matt

I gave the intake tract a thorough cleaning a few days ago -- TB, MAF, rubber boot (lots of oil in here), idle valve (lots of dirt, a little oil), AF (lots of oil), air box (lots of oil).

In the couple of days since, it has run fine. I'll check the gas mileage next week -- it should be virtually the same mix of city and highway as the previous week; one long day on the highway plus a week of city traffic. Here's hoping next week's numbers are better. I'll probably replace the PCV soon just to be on the safe side, but I didn't have one at hand when I had the free afternoon.