Emissions / Smog idle test fail - High CO%, causes and fixes

Hi Everyone, Did a search and didn't really find any answers; hopefully someone here has an idea. Went to get my emissions test. I figured that I would be able to get it done before doing an oil change (my mistake), so I went ahead. Took the car for a good drive and it was warmed up. Ended up failing. Not entirely sure what's wrong; the one thing I have done since then is changed the oil. Wondering if I should do anything else. If anyone has any ideas please feel free to share: Here are the results 2001 Carrera 4 2500 RPM test = Pass HC ppm = 5 (allowable 150) CO% = 0.01 (allowable 0.70) RPM = 2421 Dilution 14.1 Idle RPM test = Fail HC ppm = 80 (allowable 150) CO% = 4.46 (allowable 0.70); yes 4.46!! RPM = 788 Dilution = 11.1 Again, if anyone has any ideas please let me know. Would an oil change fix all of this? The mechanic said prior to the test, that if there was no CEL, the Porsche would be fine. After the fail, he said perhaps the oxygen sensor as he thinks its running rich, however no CEL is present.

Here is part of a post I made a while ago, after failing CA smog with my 996 and my wife's SL600...."On the same day that I has the Porsche retested, My wife brought her 2001 Mercedes SL600 (with 55,000 miles) to have it smog tested also. It failed...at 15 mph it had 47ppm of CO2...passing was 44ppm. It is completely stock and runs perfect. I went to Kragen and bought a can of CRC "Guaranteed to Pass" additive and followed the instructions. I just came back from having it retested. I was hoping that between the additive and really warming the cats up, it would drop the 3ppm necessary to pass. It passed with the CO2 reading at 4ppm (down from 47). All of the other readings were at about 0ppm. Both the tech and I were amazed. I will never take a car to have it smogged again without adding that stuff. For less than $10, it was money well spent." __________________

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Unlikely the oil change had a hand in this. I sometimes change my car's oil before a smog test simply because fresh oil is less likely to make it past the rings/valve seals and possibly add to the HC load the converters have to process. Be sure you do *not* overfill the oil. High CO2 at idle coupled with a pretty high HC reading suggests a fueling problem. I do not know the miles on the car or its general condition, but for the first couple of smog checks I ran a bottle or two of Techron through the engine as per directions on the bottle a few gas tanks before the smog check. This is to remove any fuel/combustion chamber deposits. Now I've done this and not done this and the cars still pass though the Boxster's number are worsening mainly due to the age of the converters. But your car's engine might benefit from this. I can't recommend any fuel additive touted to help the engine pass smog. I don't doubt those that do make claims these additives work, it is just that I've never had any experience with the these additives. What are the plugs like? Be sure the plugs are fresh, or at least not too old. Be sure you run a name brand premium grade of gas on a regular basis (at least a few tanks before and during the test). Be sure the engine air filter is fresh and installed correctly. The short/long term fuel trims and O2 sensor readings might be of some value taken at 2500 rpms and at idle if you can provide them. Sincerely, Macster.

Just did my e-test, and yep failed miserably. Idle CO%= 5.x allowed = 1.0 Along with most of the other tests as well. So what did you do to fix yours?

Do you have any 'soft' codes (that don't turn on the cel) in memory? - Age of coils, (condition as well). - plug condition as was mentioned by Mac - MAF? These are insidious little pieces of BOSCH technology that when either dirty or just s_l_o_w_y failing can cause hair loss. - O2's? - very dirty air filter?

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Since my last post on this thread my 02 Boxster failed its last smog test. IIRC the HC's were high in at least one of the two RPM ranges. This caught me by surprise. I dashed over the dealer and separately spoke with two senior techs about this. Both were surprised the car failed emissions. Both said that without a hard converter error that I should take the car out and give it a nice run. No Italian tuneup -- well maybe a little -- but take the car for at least a nice long drive. Now before the test I had driven the car around quite a bit -- > 30 minutes -- so I was sure the engine and exhaust system were fully up to temperature. And before the test while getting the paperwork done I let the engine idle. I headed out east on the freeway and drove 15 miles or so then pulled off the freeway on to a road that runs through the mountains between the central valley back into Livermore (CA). On this road I gave the engine some whip. Before the road got into the most curvy parts I turned around and drove back to the freeway and got back on the freeway and turned towards home. (Well, the smog test station.) Had to follow a CHP cruiser the whole way back but the car passed smog back at the smog test station. The HC readings were well down into the passing range. In your case if the engine is not overfilled with oil, if the gasoline is reasonably fresh and a top tier fuel -- I avoid discount gasolines sticking with mostly Shell but I have used Chevron (which is the brand Porsche uses for its USA emissions testing) and Philips 66 and Unocal 76 -- and there are no active or pending DTCs (which there probably aren't as the smog test tech would have failed the car for these even before testing) my advice would be to take the car out for a nice highway run. If you manage to find a place where you can safely hard accelerate up through at least a couple of lower gears that would beneficial. But try to pick a route that allows you to cruise the car at a steady highway speed. You can use top gear -- no need to buzz the engine -- the idea being the engine want to work at a steady load for a while the idea being this helps remove engine deposits and helps remove any deposits in the converters. If after the above the engine passes, then you know. If it doesn't pass then there is an underlying problem. But with no error codes to go on I would be hard pressed to offer anything but some WAG's as where the problem might be.

You are running rich at idle. Look at the dilution.

Thanks for the tips. I'm kinda posting in the wrong thread cuz I have a 93 RS America (964), but the basic premise of cleaning up bad exhaust should be the same. My baby isn't throwing out any error codes but it prob doesn't even have too many to throw anyways since it doesn't have all the fancy new electronics. I did change the plugs and wires and coil packs and did a tune-up and changed EGR valve? and O2 sensor last summer (barely drove it this summer). I drove it for 45 mins before I got to the test centre and drove straight in, but it was via super high traffic areas so didn't get up through the gears. (I was on the 401 at 4pm, yes from Toronto too ). I always fill with 94 gas. I'm going to try the Guaranteed to Pass stuff for $14. I can't see any posts about this stuff blowing up your engine so for $14 might as well try. I'll post all my results when I get home. I think the dilutions were fine.

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Well, do what you think best. If you want to try that additive that's entirely up to you. Based on the info in the quoted post, my take away is the gasoline is probably quite stale and this accounts for the emissions test failure. Thus my advice would be to drive the car around until the fuel level drops to say 1/4 tank and refill with fresh 94 octane fuel and drive some more then go have the engine re-tested.

Why did you change all those parts, were you chasing a problem?

Thanks for your help everyone. Well the valve was changed because often the throttle would just stay open, ie the car would keep going steady speed until I blipped the throttle or the brake. And the 02 sensor looked dark/burny and the wires plugs look like they hadn't been changed in a long time (I had just bought the car). I added the guaranteed to pass stuff, didn't make a huge difference. In Ontario Canada, if you spend *upto* $450 on emissions repairs, you get a conditional pass and can drive for another two years. It was the best option at the time. (ie no time to play around since winter is just about here and time to park it soon anyways).

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That gasoline is going to be very stale come next spring. I"m not sure I'd put the car away with stale gas over the winter. If you can't drive the car enough to run the stale gas down then maybe you should have a tech drain the gas from the tank and then go fill it with fresh gas? If you want to use a gas additive afterwards that's up to you. A 1993 911 doesn't have the more sophisticated OBD2 hardware, so without any error codes to go by, just high CO% numbers with fresh plugs and no untoward behavior from the engine -- no rough running, stumbling, blubbering -- no indication the engine is running rich I'm not sure where to go from here. Let's see my references for the 1989/1994 C2/4 964 are that the engine does not have a secondary air injection pump, has an idle stabilizer, uses Bosch FR5DTC (or?) Beru 14FR-5TDU plugs gapped to 0.7mm, has a DME double ignition, should idle at 880 +/-40 RPMs, CO% at idle should be 0.4% without converter, has a 3 way converter with heated oxygen sensor. You replaced the oxygen sensor. Just one? Or are there two? Also, you replaced the plugs but from my reference there are two plugs per cylinder. Did you replace both plugs per cylinder? What did the plugs look like? The 964 engine comes with 2 plugs per cylinder. 1 set of plugs is sparked by a distributor driven by the crankshaft. The other set of plugs are sparked by a distributor driven by a cog belt by the 1st distributor, This belt can snap and then only 1 set of plugs are getting sparked. If this has happened with your car's engine this can result in one of two plugs per cylinder not firing at all and this can certainly account for a high CO% reading. My guess is an experienced Porsche tech has had to encounter this problem before and should know what's wrong. So come next spring I would advise you to get the car to an experienced tech and let him help you.