spoon2000

Very easy fix. Removed engine covers, removed a couple sections of air intake tube, pulled the old sensor, replaced with new sensor, new gasket, and new clip, then replaced air intake hose sections. Would have taken 15 minutes at most under ideal conditions. Flathead screwdriver was the only tool required to loosen hose clamps on air intake tube, slide out C clip, and fish the old o ring out of the fitting.

A couple notes:

1) The car was cool when I did the job and I'd removed the cap from the coolant bottle, but I still lost all the coolant that was in the overflow bottle when I removed the old sensor. I don't know how this could have been avoided given the laws of gravity.

2) I was able to shine a light down on the new sensor and confirm that the C clip was going into place correctly when I was sliding it in.

3) In the process of removing the old sensor, I managed to snap off the small retaining clip from the harness. To avoid replacing the harness, I plugged in the new sensor then simply secured it with a piece of copper wire (from the inside of a piece of cable TV coax) that I looped through one leg of the C clip and then twisted with foreceps to make it tight.

4) I put on safety glasses and wore a heavy rubber glove when pulling the old sensor -- wanted to be protected in the event that coolant sprayed or got flung somehow.

I'm including a few pics in case others are interested. They show the engine bay with hose removed, the old sensor still in place, the before and after parts side by side, and the new sensor installed and secured with wire.

spoon2000

Answered my own question (I think) -- best access is from the top after removing the coolant bottle.

charles 200TQ

So were your cold-start issues solved?

spoon2000

I would say the cold start surging is better, but not yet completely resolved. Moreover, it's in the low 60s this morning, which is not quite cold enough for the car to really misbehave. So I'll do the O2 sensor next and see what difference that makes (and hopefully that will affect low gas mileage, too!).

Edd W

Cannot really help as I have no experience on the 4.2, I have a 2.7t.

spoon2000

For a savings of $60 and to avoid having to order and wait for an OEM sensor, I decided to go with the generic O2 sensor over the OEM version. The markings, wire colors, etc. of the old sensor were nearly identical to those on the new one so I'm assuming the old one was also a Bosch like the new one.

It was surprisingly easy to get the old sensor off -- drained and removed coolant bottle, applied some liquid wrench to the old sensor threads, then just reached down with a short O2 sensor socket (on loan from Advance Auto Parts) -- here is the kit from Amazon: http://www.amazon.com/dp/B0028QGTNG/...SIN=B0028QGTNG -- and used a 3/8" socket wrench to unscrew the old sensor. Very easy to cut and splice the wires of the new sensor to those on the existing connector. Reversed process to install the new sensor.

Erased codes via VAG-COM and will see if they return. Gas mileage appears to have improved 1-2 MPG, although I won't know for sure on that without further driving. Surging still exists some but is better.

If the O2 sensor and CTS were the cause of the cold start surging, would replacing them solve the problem immediately, or would it take a short while for the car's computer to adjust to them?

Edd W

It should be immediate. The CTS and O2 are real time and adjust fueling continuously. Re-scan codes after a day or two of driving to see if all is well.

Redneck Truck

Hopefully you'll change the right combination of parts for it to run perfectly again.

Edd W

The idea is that after releasing any residual pressure in the system, you re-tighten the reserviour cap, that causes a hydralic lock which prevents any great loss of coolant.

The only thing I would add is to sqeeze a coolant hose to raise the level of thye coolant just as the sensor is pushed back in to make sure you do not add any air locks.