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Car is a 91 LS Wagon 5sp with 230km's. Took it in for testing and it failed the CO% test.

IDLE Limit =1.00 / Car did 2.26
2500 RPM = 1.0 / Car did 7.27

I don't have the test results from two years ago but I do recall the car passing with flying colours. Since then two main things have happened.

- Header cracked at Y joint at the bottom of the car. This was welded closed about a week ago.

- Car was suffereing from erratic idle. Had the mechanic check for that valve sticking and he said it was siezed. He turned up the idle to 830rpms and it idles fine now.

Oil/air filter was last changed early in the summer, the car is barely driven until the winter time. When the car passed the last time it had dirty oil/air filter/plugs etc...

The emissions facility guy figures it could be an O2 Sensor. Any suggestions here ? Did a search and did not find anything relevant.

O2 sensor would be a good guess. Has it ever been replaced?

The car was well warmed up when you took it for the test right? IE: 30 minutes or so on the highway, and then right in for the test? If not, the catalytic converters may have been cold, which would contribute to the higher emmissions.

How did your mechanic raise the idle?

I failed once, replaced the o2, and passed very well.

HTH

Take your gas tank really low. Go to store and buy about a liter of isopropyl alcohol (rubbing). Put in the tank, mix. Drive the mess out of the car on the way to the testing station (to make sure it is good and hot). Pass with flying colors. Drive IMMEDIATELY to a gas station and fill up all 15.9 Gallons.

If this will get a 1984 Delta 88 with a 4-barrel 8 cylinder 307 c.i. engine to pass with barely registering numbers it should work on your car, too.

But get the 02 sensor anyways, since you are losing horsepower if that is bad.

mikec wrote:O2 sensor would be a good guess. Has it ever been replaced?

The car was well warmed up when you took it for the test right? IE: 30 minutes or so on the highway, and then right in for the test? If not, the catalytic converters may have been cold, which would contribute to the higher emmissions.

How did your mechanic raise the idle?

- I've never replaced the O2 sensor and had the car for only 30 out of 230 k's. I would assume "NO" is the answer.

- Car was nice and warm ran some errands and came off 10 minute run down highway right into the test bay.

- Not 100% sure how he raised the idle.

Brat4by4 - that's an interesting idea. Is there any factual data behind that ? Curious where you got the idea from. Could it cause any further damage ?

Alcohol burns clean. Leave it in too long and it will start to eat all the rubber parts it comes into contact with. But that is over an extended period of time IIRC.

I've heard of doing that too, with the same warning to flush / dilute it as soon as the test is done.

You shouldn't need to cheat by running alcohol or anything like that. These cars should run pretty clean. Some board members pass emissions tests without any catalytic converters.

Running errands and then cruising down the highway doesn't really get the car nice and hot. Cruising on the highway is actually pretty easy on the car. You should drive the snot out of the car, hitting redline at wide open throttle a lot, to get it ready for an emissions test.

Your mechanic probably didn't know what he was doing, and "turned up" the idle by adjusting the throttle stop screw. Said screw should never be adjusted by anyone. The computer is meant to control idle speed through the IAC valve. If the IAC valve is sticking, you might try cleaning it. A search on this BBS should yield a few threads about IAC valves and cleaning them.

Take a look at the throttle stop screw. After its position is calibrated at the factory a stripe of white paint is applied to mark the position. If you're lucky you can still see this paint and get it back in position.

You might also want to clean out the engine with some Sea Foam. Again, a search will yield the procedures a few of us use. It can't hurt.

It could be a bad oxygen sensor. A high carbon monoxide number seems to indicate the engine is running rich, which a bad oxygen sensor could cause it to do.

My car passed emissions testing with flying colors with the oxygen sensor disconnected, so maybe you could try disconnecting the sensor, resetting the ECU, and then taking the test again. Or just replace the sensor if you suspect it's. A new sensor works much, much better than an old one, even if the old one isn't bad.

As everyone else has mentioned....these cars run really clean.

I'd probably start with the O2 sensor and sea foam.

I'd also possibly suspect there's another issue somewhere that is the root of the problem for not passing.

The computer is meant to control idle speed through the IAC valve. If the IAC valve is sticking, you might try cleaning it.

Yes, the IAC valve was what I was referring to. He said it was totally siezed and cleaning it didn't help. I know we're not supposed to move the idle but the car was stalling on an almost daily basis which is a little more important to me when I'm stop & go in rush hour.

I'm going to try to bring it in tomorow and have him look at what's causing the CO readings. DO you really see any harm in raising the idle manually ?

At best, blocking the throttle open reduces the adaptability your car's supposed to have to various situations. Yes, if you need the car to not stall out you have little choice. But I'd recommend picking up a used good IAC valve as soon as you have a chance. I don't know for sure, but it could affect emissions somehow. You throw off the idle switch reading and stuff.

I dunno. It's probably not the reason your car failed the test, but it is something that's keeping the car from running how it was meant to.

You might want to try cleaning the MAF sensor.

I think I am going to go and take a voluntary, cattless test. I want to see just how clean the car runs without any cats at all.

If I pass, then that would be really cool

had the biannual emissions test. Hadn't driven the car since january, used the january gas. Presumably original o2 sensor. Completely stock powertrain.

51 hc at idle, 8 at 2500rpm ---- max allowable 120, 140
.05 co at idle .03 at 2500rpm ---max allowable 1, 1

Yeah, i passed

Pretty happy about it since i haven't driven the car in so long.[/code]

02 sensor is a must, my car was failing like i had uncontroled 800cc injectors before i replaced it.

i had to raise the idle on mine to get it to pass after a full tune up with 02, plugs and wires, because i was dumping too much fuel on a low idle. my co was fine it was my hc's that were up.

raised the idle to 900 and passed cleaner than i did last year with 2 cats.

after the test was over the idle went back to normal

I'll add my vote for SeaFoam and a new O2 sensor. Get that IAC valve replaced as soon as you can as well, as I'm sure that did not help any. . .

Passed with numbers similar to what scott gave and that was before I replaced the O2 and ran a can of SeaFoam through it. Since then the car has "perked up" like it was woken from the dead. . . I'll bet my numbers are a lot better now. . .

Ouch, my original understanding of how fueling was wrong, I admit that; thanks for the corrections vrg3.

So could you please clarify, how does the ECU determine no load fuel requirements initially; aside from the use of the O2 sensor for the ECU to adjust fuel requirement?

Where do you get the idea that the ECU has a separate idle fuel map?

And that the ECU's strategy for closed-loop fueling is different at idle than at low load?

Or that the fuel computations are inaccurate in no-load situations?

Or that fueling is based on a map at all?