The dreaded and irrepressible INTERMITTENT Check Engine Light - ANY NEW SUGGESTIONS?

(I'm desperate and am also posting on Rennlist - tired of this chase....) CAR: 2002 Porsche Targa 3.6; about 160,000 miles; always regularly serviced at Porsche dealership prior to my ownership, with records at the dealership. I bought this car over a year ago, and within a couple weeks, the cel came on. The car was running fine – no problems except the presence of the light. We reset the light with our OBD-II tool – the code (P0491) had something to do with the secondary pump malfunctioning (actually “insufficient flow to Bank 1” – see at the bottom of this post for the various interpretations I have gathered). The light stayed off for a few more days – then re-appeared. The car continued to run beautifully. Well, for more than a year now, the light continues to come on every few days to weeks – highly variable, but seems to be related to the car sitting in traffic or with extensive idling. Yes, the car runs through enough cycles for the light to have turned itself off after repairs or resets. We reset it every time. In fact, my wife carries the code reader in the car and resets the light as if it were part of a usual routine. I read many threads on Porsche forums about cel problems – and the thousands of dollars that members have spent trying to track down the causes, and a usual outcome being A TEMPORARY FIX, but inevitably a recurrence of the trouble light. I finally decided to have it checked out by a local Porsche Indy (Lutzo at LMN Motorsports – one of those ace, and completely honest, independent mechanics in the area). Lutzo has all the Porsche factory diagnostics, plus decades of Porsche experience. He went down the Porsche factory diagnostic list and chased the various possible causes, including MAF, piping, O2 sensor, SAI pump checked for operation, even smoke tested for leaks. He called the factory asking about other possible solutions. He swapped out parts on a trial basis (no charge) to see if the problem was solved. I had the plugs and air filter replaced just for general principles. The problem was localized by the diagnostic machines to the first bank cylinders only. The MAF and the secondary pump both checked out OK; the hose that runs under the manifold TO THE SECOND BANK seemed to be leaking (could not get it to seal where it attached), so was replaced. The O2 sensor was over 10 years old, so was replaced. So, listing the chase so far: new plugs; new air filter; new O2 sensor; new SAI tube to Bank 2; MAF checked with a replacement; SAI pump operation checked; smoke test for leaks. In addition, there have been HOURS spent by an expert Porsche mechanic trying to track this down. Every time we thought the problem was fixed, a few days/weeks later, boom, on pops the cel again. I finally gave up – the recurrent 60 mile drive to the mechanic was ending like the horror stories in the Porsche forums. I think most owners just do like we are doing – reset the light and drive on. HOWEVER, HAVE THERE BEEN ANY NEW POSSIBLE SOLUTIONS TO THE DREADED cel repetitious and intermittent recurrence? Below are the various definitions of the P0491 code, as well as a partial list of Porsche forum posts (Pelican and Rennlist) with similar “cel” problems, but highly varied causes and outcomes. http://forums.pelicanparts.com/porsche-964-993-technical-forum/294749-ignore-check-engine-light.html http://forums.pelicanparts.com/porsche-996-997-forum/442891-check-engine-light-popped.html http://forums.pelicanparts.com/porsche-996-997-forum/826633-obd-error-codes-advice-please.html http://forums.pelicanparts.com/porsche-996-997-forum/540035-p1123-1125-errors.html http://forums.pelicanparts.com/porsche-996-997-forum/443140-error-code-po410.html http://forums.pelicanparts.com/porsche-996-997-forum/347382-obd-code-0420-a.html http://forums.pelicanparts.com/porsche-996-997-forum/560136-2000-996-recurring-check-engine-light.html CEL after deceleration from highway speed to idle - Rennlist Discussion Forums P0562 Low Voltage Fault - Rennlist Discussion Forums CEL Error: P0491 - Secondary Air Injection System Bank 1 - Rennlist Discussion Forums Day two of ownership and I already need help - Rennlist Discussion Forums 996 secondary air injection valve replacement DIY P0491 and PO492 - **SOLVED!** - Rennlist Discussion Forums 02' 911 996 Smog Pump Issues - Rennlist Discussion Forums CODE DEFINITIONS GATHERED FROM SEVERAL SOURCES: P0491 Secondary Air Injection System, Bank 1 - Insufficient Flow P0492 Secondary Air Injection System, Bank 2 - Insufficient Flow Possible cause of fault - Electrical fault in power supply or line between relay and secondary air injection pump - Secondary air injection pump relay mechanically faulty - Mechanical fault in electrical secondary air valve - Pneumatic secondary air valve faulty/sluggish - Electrical fault in secondary air injection pump - Mechanical fault in secondary air injection pump or secondary air injection pump blocked - Vacuum system leaking - Air hose to secondary air injection pump slipped off or constricted P0491 Secondary Air Injection System, Bank 1 - Below Limit Possible cause of fault - Fuse F3 faulty - Open circuit to secondary air injection pump - Short circuit to ground in the lead to secondary air injection pump - Secondary air injection pump relay mechanically faulty - Secondary air valve sluggish - Secondary air injection pump (air cleaner) blocked - Air hose to secondary air injection pump slipped off or crushed - Secondary air injection pump faulty/stuck P0491 Secondary Air Injection System, Bank 1 - Insufficient Flow P0492 Secondary Air Injection System, Bank 2 - Insufficient Flow Possible cause of fault - Electrical fault in power supply or line between relay and secondary air injection pump - Secondary air injection pump relay mechanically faulty - Mechanical fault in electrical secondary air valve - Pneumatic secondary air valve faulty/sluggish - Electrical fault in secondary air injection pump - Mechanical fault in secondary air injection pump or secondary air injection pump blocked - Vacuum system leaking - Air hose to secondary air injection pump slipped off or constricted

Quotes source post: 8320211

If your tech is absolutely sure there are no cracked or disconnected lines in the SAI system, pull the vacuum tank and check it out of the car. We found the reservoir tank failed on one car. It didn't leak using a smoke machine and I didn't find the leak until I submerged it under water and applied air pressure to it. Drove me nuts trying to cure the secondary air codes. Some times the only recourse is to remove the entire SAI from the car and check each component on the bench.

Quotes source post: 8320378

Thanks. I appreciate that you have experienced this problem before, as opposed to the numerous and sometimes random suggestions I have gotten. I am making a list of items to check, and if low cost (under $25 each), will replace one by one. I don't have the capability to check the vacuum tank, but will check how easy it is to remove, and maybe take it somewhere or replace it down the road. Will keep this post alive as I progress over the next few months.

It is isolated t the SAI. Focus on that and nothing else. This is simply a process of elimination and there are only a handful of possibilities. This can be fixed.

Quotes source post: 8321152

Yep, will plan an economical approach.

Secondary air systems are quite simple.....I've had a few stump me but always figured out the problem, i second checking the vacuum resivoir......that's usually the killer.....as if it's got that leak under vacuum (which won't show up under a pressurized smoke test ) it won't have enough vacuum to open the sai valve.......you can stick a hand vacuum pump on it directly, if it won't hold vacuum that's your problem....along with the tech that possibly didn't check this during his multiple diagnosis....but we'll give the benifit of the doubt until you find the problem....

thanks to all so far. This forum is incredible. No where else would I have gotten such expert advice for such an arcane problem.

Yes, the dreaded 0491 secondary air. I got my first a month after I bought the car (2002 996) My nephew cleared the code and it was good for another month. YES, it returned so I decided to give it the "Italian tune up" 2 can octane boost, 10 gallons premium fuel, 1 can of fuel system cleaner, a major highway, radar detector and 7000rpm for as long as you can. It's been 4 months and it has not returned.

Hmmm. I did try two containers of Techron in half a tank of gas (treats 40 gals). I'll get some octane boost and give a try. I prob need to drive it a couple hours at highway speed (or greater)

Did you check the vacuum resivoir?

Quotes source post: 8356126

Not yet. It has gone to the back of my list; I'm hoping for a magic cure, ya know...

I can't help with any technical support for you particular CEL code. What I can help with is that in the past I have had CEL's and reset the light with my OBD II. Two in particular would come back on later after many miles. Eventually the CEL quit lighting up and I did nothing but reset it. I know this is not the proper way to go about it but the way I saw it was, maybe they were spurious. Those two codes have never triggered the CEL in over three years now. The most important CEL light for us negligent Porsche owners is the one that blinks. That means "get it fixed now." Happy motoring and don't stress out. I am hoping it will go away like the two I had over 20,000 miles ago.

Quotes source post: 8357745

Funny thing. It has not come back on for over three weeks now. As I said earlier, the wife carries the OBDII code reader/reset tool in the back seat, and resets it as fast as resetting the trip odometer. But I've been thru this before. It can take 1 hour to reappear, or it can take a week or two. But three weeks now.... maybe it's getting fatigued, or maybe those incantations and stupid magic gas additives might be working?