Dying 1.8 90 Golf

Oxygen sensor or coolant temperture sensor is my guess. The coolant one is a cheap and easy replacement that you can do in your driveway on a stone-cold engine in 5 minutes w/o too much mess. You might lose a little bit of coolant but not much (the colder your engine the better for this. On the engine between the 3rd and 4th spark plug wires will be a coolant fitting with two sensors in it. The blue sensor is the one for the ECU. Get a new one along with an o-ring. They're cheap...should be under $20 USD out the door. Pull out the retaining clip, pull out old sensor and o-ring, out in new o-ring and sensor, install clip, done.

The oxygen sensor is usually screwed into the exhaust manifold or right before the cat. Since you have a Golf 1.8 and not a GTI you probably have the single downpipe "RV" engine, in which case it's in the underside of the manifold. It might be hard to remove (heat may have helped seat it very well). But it's theoretically as simple as unscrewing it, unclipping it from the wiring harness connector, and installing a new one. However they're usually over $100. Rumor has it that Ford has the same sensor on its cars for much less (I think I heard about $50) and you'll just have to splice over the VW connector from the old sensor to the new one. So you can go that route if you want to save some $$$.

As the first reply said "my guess is coolant sensor". I'll "bet" it's the coolant sensor. They are cheap and easy to replace. If you have the plastic water outlets, just pull the cli off then pull out the old sensor and put the new one in using a new "o" ring.

jo bo.

Classic Coolant sensor failure.

A quick fix is to switch the wiring at the flange...ie clip the blue connector onto the black sensor and vice versa.

- Pete

Get a Bentley and a multimeter. Then test components and wiring out at the ECU plug.

Then, like everyone said, probably replace the coolant sensor. lol

I have seen the ground wire for the FI break INSIDE of the harness, so that is why I said check the wiring at the ECU plug. happy new year! later, dave Reminder........ Before you criticize someone, you should walk a mile in their shoes. That way, when you criticize them, you are a mile away from them, and you have their shoes. Frieda Norris

Another idea... make sure you're running the right spark plugs. I once threw in a set that was labeled as correct, but they were too cold.

Bosch Silber ("silver") are OEM, and they run a long time.

Tim Wohlford '89 Golf

Shhh.. it's a secret! :-)

Could be a brown sensor.

Is there a way to test the coolant sensor, with say a test light or a meter?

I think there is...has something to do with at a certain temperature and measuring the resistance across two terminals or something like that. It kinda sounds like a pain for the DIY-er because you'd have to know the coolant temperature to do the test right. Given that the sensor and o-ring is under $20 and is a easy fix (and failures aren't uncommon either), I think it's easier to just replace it. Even if it isn't the cause of your immediate problem, when your problem is fixed the new sensor usually helps improve idle and smoothness a bit anyway.

Yes... resistance at a particular temperature has to be withing the required range.

It's documented in the Bentley manual. (Unsubtle hint)

Replace the blue coolant sensor and if that doesn't fix the problem, disconnect the O2 sensor. Running smoothly now? It's the O2 sensor. In fact, with the age of your car, all my money is on the O2 sensor (assuming ALL ground connections are good).

As for the Ford replacement sensor myth. It's not a myth. I have a Bosch sensor that cross-references with a bunch of Fords yet no VW products. Motor was tuned after installation and runs as clean as can be for an '89 Jetta:

HC 9ppm O2 0.92% CO 0.00% CO2 14.65%

If you're in Canada, Canadian Tire carries the sensor. Otherwise any UAP/NAPA store will be able to help. You'll need a 22mm open-end wrench to do the work.

Bosch 13913 CDN$80.93

You can cross-reference to Echlin and other O2 sensor manufacturers but stick with Bosch.

:-) I knew it was but it was in the other room and I didn't feel motivated to go look up the details at the time.

I figured as such. I just hadn't made the VW-to-Ford-Bosch-sensor change myself so wanted to make it a little disclaimer.

Understood! Should have seen the squint on my face when I first did the swap.