My 91 318is failed WA state emissions recently, and I'm trying to figure out why.
I failed on one count only - my HC emissions were too high at idle. CO emissions were well within spec.
Recent history that may be relevant: we recently took the engine apart to replace a burned exhaust valve. After putting things back together, the engine idles rough. Idle speed fluctuates between 8 and 900 RPM, and engine occasionally "shakes".
As part of the repair and subsequent troubleshooting, we checked or replaced the following:
- Air filter looks fine
- Air flow sensor, TPS work
- ICV buzzing
- New plugs
- New ignition wires
- Engine compression is good
Other potentially useful info:
MPG seems normal. I'm running 20/50 conventional oil. I don't know how many miles are on my motor since it's a used one that we picked up a few months back. Idle speed fluctuates between 8-900 RPM.
I compared my results to last year's - and found that my HC's were higher at both idle and cruise. My CO emissions were exactly the same for idle, but twice as high at cruise (though both were well under the required limits). My CO+CO2 emissions were the same as last year. My O2 emissions were half what they were last year at cruise, and 13 times higher at idle.
I think the O2 results are telling me that my engine runs rich at cruise (too little 02), and lean at idle (too much O2). Not yet sure where the problem could be, but thinking potentially O2 sensor, exhaust leak upstream of sensor, vacuum leak, injectors, potentially leaky exhaust valve (though I hope not, since we've just done the repair...). Again, I'm also giving a higher consideration to things that would have changed since we've done the repair, since I didn't have the rough idle prior to that.
So....if you'e gotten to here, thanks for reading. Any further suggestions for things to check & how to check them? Planning to dig in more next weekend. Thanks for the help!
I failed on one count only - my HC emissions were too high at idle. CO emissions were well within spec.
Recent history that may be relevant: we recently took the engine apart to replace a burned exhaust valve. After putting things back together, the engine idles rough. Idle speed fluctuates between 8 and 900 RPM, and engine occasionally "shakes".
As part of the repair and subsequent troubleshooting, we checked or replaced the following:
- Air filter looks fine
- Air flow sensor, TPS work
- ICV buzzing
- New plugs
- New ignition wires
- Engine compression is good
Other potentially useful info:
MPG seems normal. I'm running 20/50 conventional oil. I don't know how many miles are on my motor since it's a used one that we picked up a few months back. Idle speed fluctuates between 8-900 RPM.
I compared my results to last year's - and found that my HC's were higher at both idle and cruise. My CO emissions were exactly the same for idle, but twice as high at cruise (though both were well under the required limits). My CO+CO2 emissions were the same as last year. My O2 emissions were half what they were last year at cruise, and 13 times higher at idle.
I think the O2 results are telling me that my engine runs rich at cruise (too little 02), and lean at idle (too much O2). Not yet sure where the problem could be, but thinking potentially O2 sensor, exhaust leak upstream of sensor, vacuum leak, injectors, potentially leaky exhaust valve (though I hope not, since we've just done the repair...). Again, I'm also giving a higher consideration to things that would have changed since we've done the repair, since I didn't have the rough idle prior to that.
So....if you'e gotten to here, thanks for reading. Any further suggestions for things to check & how to check them? Planning to dig in more next weekend. Thanks for the help!
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