Help diagnose problem!

[Rok986]

2001 Boxster S w/ 133k miles on it. Recently developed a funny idle. Car drives fine, but feels like cars going to cut off when idling. It hasn't, but just sounds like it is, kinda like the old cars with the carburetors. Here are some clips of the engine and exhaust. Also threw P1411 and P0410 codes about a week ago.

from Rok3479 on Vimeo.

from Rok3479 on Vimeo.

[thstone]

The codes are for secondary air injection system failures. The SAI system simply injects additional air into the exhaust at cold start for about 90 secs to reduce emissions.

P0410 Secondary Air Injection System, Bank 1 – Below Limit
P1411 Secondary Air Injection System, Bank 2 – Below Limit
Possible cause:
- Secondary air injection pump is not triggered
- Secondary air injection pump does not function
- Air supply lines restricted
- Electric change-over valve does not function
- Air change-over valve does not function
- Vacuum system leaking

Does the engine idle poorly all of the time (cold, hot, etc) or only under certain circumstances?

[Rok986]

Idles poorly all the time. Funny thing is, the codes came up last week and car has actually been running fine. Poor idle just started yesterday. I drove the car around today and got the engine up to normal operating temp and idle still the same. I don't hear anything leaking, anywhere, and engine revs fine. Its just the idle that sounds lumpy.

[Smallblock454]

Hi Rok986,

besides the codes, to me it sounds more like a misfire. So i would check for an ignition problem. Sparks, spark plugs, spark lines, ignition coils.

Maybe a bad / leaking injector could also cause this, because that could cause misfire.

To me on the video from the top of the engine there is an unusual mechanically relatively loud noise. You can also hear it on the exhaust video.

If the SAI would not work, that would mean all cylinders would run too fat. But that in general would not mean that some cylinders misfire, but all and the misfire would go away if the engine is fully warmed up - let's say after 20 miles there shouldn't be that misfire any more, because the engine is fully warmed up.

Does the SAI work. So does it make that loud wining noise when it kicks in?

Hope that is helpful.

Regards, Markus

[Rok986]

Hmm, could be a leaking injector as I just ran through a tank of the moly gas additive. Maybe that's causing a misfire from some of the cylinders running too rich?

[san rensho]

Sai problems also cause vacuum leaks that can lead to rough running. Check the maf flow and the fuel trims. If the maf flow is low and tbe fuel trims are high on the plus side then good chance its a vacuum leak.

[thstone]

Originally Posted by Rok986

Hmm, could be a leaking injector as I just ran through a tank of the moly gas additive. Maybe that's causing a misfire from some of the cylinders running too rich?

What was the thinking behind the use of the gas additive? Was there a poor running condition that you were trying to address?

[Rok986]

Originally Posted by thstone

What was the thinking behind the use of the gas additive? Was there a poor running condition that you were trying to address?

No, it was running fine, as far as I could tell at least. Did it for preventative maint, but may have caused problem.

Funny thing happened this morning though. Didn't drive the car all weekend, then tried firing it up this morning and it started and ran fine! Idling normally, no misfires, so I drove it to work. Noticed it started misfiring on idle again once engine was warmed up. This is getting me more confused now. Why would the problem go away when cold, but come back when warm?

[specboxCO]

Almost definitely going to be a vacuum leak somewhere. If you have a vacuum gauge, put it on the manifold and pull off the AOS hose, if the vacuum doesn't drop much, you probably already have a leak.

[specboxCO]

Follow this flow chart to identify the issue.