Kingttr

O2 sensors are toast. He said he has had 3 oxygen sensors replaced in the last 3 years or so. He is going to find the service records so I can look and see what they actually did. Is there something that would be trashing the O2 sensors? He said the car feels like it shutters a bit too when he is slowing down (car is 5 speed manual). Any insight is appreciated. I am giving him number for indy mechanic I go to, but he plans on going to the shop he has been using first as he has already paid them to fix this problem. I know little about the place, but he said they charge 120 dollars to diagnose MIL.

Here are the codes:
16518 (P0134) - O2 Sensor Circ.,Bank1-Sensor1 No Activity Detected

17536 (P1128) - Long Term Fuel Trim mult.,Bank1 System too Lean

16523 (P0139) - O2 Sensor Circ.,Bank1-Sensor2 Slow Response

16555 (P0171) - Fuel Trim,Bank1 System too Lean

77'911

Check for silicone sealant. You might see if the intake gasket has any, or anywhere before the O2 sensors. Its needs to be R&Red to change out the speark plugs(2.0 eng.). A less then intelligent dealer tech pulled this one on my sister's old jetta(01). If its the orginal sensors, then replacement would not surprise me. VW's maintenance schedule leads to this, after about 60-70k. You might have him change out the head/coolant temp sensor while you're in there.
For the shutter, check state of tune(plugs, filters, TB) and motor mounts. I upgraded some of the mounts on my sister's car to urethane, huge improvement. Sorry if this is broken up, typing too fast, hope this helps.

Kingttr

Just to make sure I understand, you are suggesting that silicone sealant (if present) is problematic?!

He said he has had them replaced before (a total 0f 3 trips/sensors). This doesnt really make sense though (2 would be understandable). I'll check out mounts, but I think he is suggesting that it is more like the engine stuttering, as opposed to driveline movement.

77'911

If it gets into the intake stream at all, it eats O2 sensors. This is why you'll see many sealants that are sensor safe being used near or on the intake and combustion pathway. After you've installed a fresh coolant sensor, clean out the TB and run an adapt with the VAG-Com. You'll find it will make a marked improvement. If you want better then that, address the previous tune-up parts I mentioned. I re-tensioned the timing belt on hers, but could have gotten away with out it. When I was done with my sister's car, you could balance a champagne glass on the intake manifold at idle. Those transverse set-ups are not exactly the smoothest running and need a bit of attention. The driveline mount system is a weak point and tranmits a far bit of vibrations through the chassis unless addressed. Having said that, I found in a number of MK4 chassis I ve worked on, 60k seemed to be a break point for many of the bonded rubber components. Happy Holidays to you and your family, hope this helps.

starting ...

i have changed the plugs on a 2.0 cabrio without taking the manifold off

Kingttr

work myself. Not that he doesnt trust me, but he would want to take it to a mechanic. Additionally, I don't have the time. The info you have given me will help though as I now know what to ask mechanics about. They have just replaced the sensors each time, not addressing the root problem.

77'911

You might ask him if the techs changed them out because they saw a code come up on the VAG computer or the O2 Sensors ohm-ed out to be bad. Depending on the service history, poor detination quality can throw O2 sensor CEL's.

77'911

Yea, you can get away with it but the chance of cross threading is much greater. I like to vaccuum out the spark plug galley before removing them so debris does not fall down into the chamber. Its surprising how much stuff gathers in there.
With the intake out, I like to change out the valve cover gasket, pcv, and clean out the tb before buttoning up the engine. Those 3mm vaccuum hoses are an easy r&r while in there as well. This way I know its fairly bullit proof for the next 20-30k or so.

Audi Junkie

I can't do it. Need to use that special tool.