New 318is failed idle smog test

[agealy]

A few weeks ago, I picked up sumyungguy's 318is, which has been great so far. Initially he thought that it had been smogged recenty enough that I wouldn't have to do anything, but it turned out the purchase was just a few days after the 90 day smog cutoff. I registered the car at the DMV, but they insisted that I get a new smog certificate.

I finally got around to getting it smogged again today and the car failed the idle test, but passed the 2500rpm test at only 11ppm (the max allowed is 140). The car has an intermittently surging idle that apparently has been an elusive problem to solve. About half the time, it idles smoothly at 800-900rpm just like it should. The other half, it'll surge up to about 1200 or 1300, then immediately drop back down to maybe 700 or so - just enough to feel rough for a moment - then immediately surged back up 1200 or 1300.

Would you think that the smog failure was due to the idle issue or could it be something else? And what could be the underlying cuase of the idle problem?

[KenC]

Idle control valve?

[sennasixty8]

did you get it nice and HOT before rolling into the smog dyno? change oil, oil filter, air filter (if dirty) and make sure you've got fresh gasoline.

don't shut the car off waiting for the tech, and talk to him before you re-run the car. That way he can set things up and you make a bee-line right onto the smog machine after heating up the car/cat.

[agealy]

Idle control valve?

The P.O. said he cleaned the ICV and the AFM, which seemed to fix the problem but it soom came back. Maybe that's still a possibility - I don't know

did you get it nice and HOT before rolling into the smog dyno? change oil, oil filter, air filter (if dirty) and make sure you've got fresh gasoline.

don't shut the car off waiting for the tech, and talk to him before you re-run the car. That way he can set things up and you make a bee-line right onto the smog machine after heating up the car/cat.

I wouldn't think that a hot cat would help much since the car did fine on the 2500 test. I'll try to do that when I get it inspected next though.

Right now the P.O. suspects a leaking vacuum hose. Does this sound like a reasonable possibility?

[agealy]

Alright, so we did some investigating and found a couple loose hoses connected to what appears to be the fuel tank breather valve. Please correct me if I'm wrong on this. Anyway, we bought a couple hose clamps for the fitted piece between the valve and the throttle body. We also replaced the 1-inch hose coming out of the other end of the valve and put on some spring clamps we had laying around. After we did this, the connections were much firmer.

I drove it around last night and it idled just fine. Today it bounced on probably two occasions, but less than usual and for a shorter time. Could this have anything to do with my problem, or was it just a coincidence?

[sumyungguy]

Looks like your getting to the bottom of it, I'd still recomend getting rid of the "birds nest". I gave you the gaskets, just get the lines and a couple of hours and I think you'll be set. I'm positive it failed smog cause of the idle, it didn't have that problem when I smogged it 91 days before you bought it.

Its good practice to reset the ECU after working on it to let it relearn.

[scabzzzz]

Alright, so we did some investigating and found a couple loose hoses connected to what appears to be the fuel tank breather valve. Please correct me if I'm wrong on this. Anyway, we bought a couple hose clamps for the fitted piece between the valve and the throttle body. We also replaced the 1-inch hose coming out of the other end of the valve and put on some spring clamps we had laying around. After we did this, the connections were much firmer.

I drove it around last night and it idled just fine. Today it bounced on probably two occasions, but less than usual and for a shorter time. Could this have anything to do with my problem, or was it just a coincidence?

I would say no that is not your problem. The fuel tank breather valve is used strictly for ventilation of the fuel tank. No affect.

For a lumpy surging idle, you'd want to look for replacing the idle control valve. I'd also check the specs of the throttle body as well and make sure its opening and closing properly and has enough clearance. Check bentley for the clearance.

[devonjordan]

Looks like your getting to the bottom of it, I'd still recomend getting rid of the "birds nest". I gave you the gaskets, just get the lines and a couple of hours and I think you'll be set. I'm positive it failed smog cause of the idle, it didn't have that problem when I smogged it 91 days before you bought it.

Its good practice to reset the ECU after working on it to let it relearn.

That medusa's head thing isn't that hard to do. I did it in 2 hours, and it helped with my idle a bit...

Also, when put everything back together, the ICV unplugged itself, is yours still plugged in?