Running lean?

[Yellow 13]

Ok, We got my cousins HG replaced and now the car shudders pretty bad. It only seems to do it at cruising with my foot lightly on the gas. When I let off the gas or floor it everything is how it should be.

CEL is giving me code 25.(running lean; or bad O2 sensor maybe)

The engine free revs in park beutifully, no bog or hint of anything wrong. Its only when the cars in motion at like 25+MPH that the shuddering happens.

I figured I could trick the computer by advancing the TPS and making the engine think it was getting more air so it would give more fuel. Nothing changed so I put it back.

I got suspicious and started to think the driveshaft could be the cause of vibration. checked the driveshaft. Pushing on front shaft near the center bearing theres about 1/2 CM of play.


Anyways PLEASE HELP ME!!!

 

[mickyg]

I had a very similar problem on my wife's 626 and it turned out to be a fault in the O2 sensor wiring. Have a look at the wiring from the sensor to as close to the ECU as possible. In fact, if you can backprobe the sensor (involves piercing the O2 sensor insulation) and do a resistance check where it feeds into the ECU, that should tell you whether there's a wiring problem.

There are very low voltages that ride on this line so you need a good connection from the sensor back to the ECU or problems will occur. At a guess, I'd say you want a quarter of an ohm of resistance or less. If you've got a good meter, this won't be a problem to test.

 

[Yellow 13]

Thanks. The previous owner did a pretty bad splice job installing a bosch O2 sensor. Im gonna start by replacing the sensor since it was working before the rebuild.

 

[mickyg]

It's certainly a good place to start! Let us know how it goes.