Car runs perfect with the O2 sensor unplugged. Plug it in and the car runs rich at times and will not excellerate and then "click" it goes...and back again. At a steady cruise you can also feel it change, bog down a little, and then back to normal.

O2 sensor is new, but the wire was melted after my rebuild and they spiced it back together, claim it ohmed out correctly. If the DME is bad what are the chances that just the part that talks to the O2 sensor is not working properly?

 

Also does not idle as well with the O2 sensor connected.

 

You cannot splice these back together. Get a new sensor dude.

Ask them how they tested it - the correct answer is with butane (between you and me)

 

Get a new O2 sensor. You can use a generic 3-wire O2 sensor just replace the connector with the stock one. (wires must be cut as close to the connector as possible)..

 

Thanks you two. If you can splice in the generic one. Why could the original one not be spliced back together? The current one it spliced at the plug and where it melted on the down pipe.

Bad to drive the car with the O2 sensor unplugged? Not my daily driver.

 

I had the same problem but more seviere. It took a bit of hunting to find the problem. I replaced the O2 sensor and it runs perfect.

 

When you unplug the O2 sensor the DME reverts back to its internal fuel and ignition mapping and doesn't try to adjust fuel at idle or cruise to achieve the afr numbers Porsche or the after market chip maker programmed in for economy or emission requirements. The fixed maps from my experience tend to run a bit on the rich side. Probably not bad but it is better in most cases to have the O2 in and have the whole system working correctly. At wide open throttle there is no difference as the DME isn't looking at the O2 signal IIRC.

 

How and where the splice was made could be the source of the problem.

For starters, the O2 sensor needs to sample the ambient atmosphere (outside air) to get a reference. This sampling is done through spaces between the insulation and the conductor strands in the signal wire. If the signal wire is solder spliced, or if the insulation was melted by an external heat source, then the O2 sensor cannot get a reference sample. There for, if the repair shop did not remove ALL melted insulation, and/or made a solder splice, the sensor will not work properly. This is why ALL sensor manufacturers recommed using crimp style butt splices.

I would start by "back probing" the O2 sensor signal wire with a DVM (Digital Volt Meter) and read the sensor out put. At idle with the sensor connected to the DME you should get a varying output. With the sensor disconnected from the DME you should see between 0.60 and 0.90 volts DC.

 

Sure sound to me like the shop that did the rebuild owes me a new O2 sensor and should have know better than to splice it back together.

Wonder if they will repay me the $275 I just spent with another shop to get the idle straightened out. Cold day in hell.