O2 Sensor

[NC325i]

I have a '92 325i 4 door sedan automatic. Ive noticed the engine doing some funky stuff. In detail, the engine will rev up and down slightly when the gas pedal is held in a constant position. Ive noticed a decent power loss also. I was told by a buddy that I might need a new 02 sensor, but he is not a mechanic.

My question is: Is there only 1 sensor on these models? And where might it be located? Also, if anyone reads this and might have another idea of what is causing this to happen, then please chime in.

Thanks! [driving2]

 

[Kirby]

The O2 sensor can cause this, did you get a check engine light? The O2 sensor is located on top of the catalytic converter. It's a pain to replace due to the position, but you can do it yourself.

Also, old spark plugs can cause this symptom.

 

[NC325i]

No check engine light as of yet. I just replaced 2 ignition coil packs that corrected a horrible miss in the engine. Now that the miss has been fixed, I can feel the surging of the engine as I drive it. I pulled all the plugs before I fixed the coil packs, and all 6 plugs were new.

Thanks for the response. This will help me feel better about sinking the cash for the sensor.

 

[Kirby]

I had this surging issue on my 325. After replacing the sensor, it was improved, and after replacing the plugs, it was gone. You can get the sensor for about $65 online at several parts suppliers.

If you do it yourself, you need a fairly big wrench - somewhere around 18 - 19 mm if I remember correctly. The location on top of the cat, and the lack of clearance make it challenging to do with regular tools, but it is doable. There is also a special tool available to make it alot easier.

 

[f1racer77]

just curious if you checked the mass air sensor. Surging could be cause by the Mass air sensor trying to over compensate for a change in airflow that isnt there.

 

[f1racer77]

just curious if you checked the mass air sensor. Surging could be cause by the Mass air sensor trying to over compensate for a change in airflow that isnt there.

 

[NC325i]

Hmm.. Didnt check the mass air sensor. Where is this located, and how would one check for problems?

Thanks for the help.

 

[f1racer77]

located just after the airbox. its the round tube with wires coming out of it. One method of testing it to remove it (5min job), hold it up to a bright light, and look to see if any of the fine wires inside are broken. Another problem (bit of a guess) is carbon deposits on the heads and pistons. Lucas makes a product that works wonders. I've seen it do wonders on push rod V-8 heads.

 

[NC325i]

While looking at the mass air sensor as mentioned above, I noticed 2 tubes that were unplugged from the back of the air box. Both are supposed to be connected to the air box, but they were pulled out and closed off. The plastic valve peice that connects the box to both the tubes is missing. Im thinking the previous owner must have broken it and just didnt bother to try to locate a replacement. Not sure if this is what is causing the surging in the engine, but its as good a start as any to fixing it.

Im not sure exactly what those 2 tubes do. One runs past the air mass sensor, and the other runs to the engine. Ill look into finding the missing part tomorrow. Hope it works.

Thanks again.

 

[cja@uwalumni.com]

I had a mass airflow sensor go - but it was very difficult to keep the car moving unless at high RPM's. O2 sensor seems like a good guess. Either way, have a shop run the diagnostics - figure out the issue and do it yourself. I save about $300 replacing my mass airlfow sensor on my own - a screwdriver and 5 minutes (not including locating the part of course).

 

[f1racer77]

those tubes should run to near the throttle body. they carry coolant. the part removed is a thermostat.