Secondary Air Injection/Idle Question

[tornik550]

For about 1 year I have noticed that after my car is warmed up, idle seems a little rough. If you pay close attention you feel an occasional very slight shudder- similar to when a engine misfires. I hooked the engine up to my durametric system and it does't appear that I am getting any misfires. It didn't seem to be causing any issues so I just left it. I then put cat bypass pipes on and the idle issue became much more apparent. Sometimes the rpms would fluctuate siginificanty and seem that the engine was about to stall. I did have a CEL on however I thought it was related to the cat bypass pipes. I do not remember all the codes that I got back then but I do remember a P0410 and a bunch of O2 sensor codes (probably from the bypass pipes). I then took the bypass pipes off and put the stock system back on. The engine has been running fine however I am getting the sight shudder that I was getting as mentioned at the start of this post. After about 1 month of driving, I got anotehr CEL- p0410.

I have read all the post I could find about this code however I really am not understanding the problem. Could a secondary air injection system problem cause the idle issue? Also, where should I start in trying to fix this problem. I do have a known good secondary air injection valve left over from a previous car. FYI- In the past I did change the AOS and I may have screwed up the vacuum hoses (I am pretty sure that I did everything correct but I may have screwed thngs up). I do not know if this could be related to the code or idle issue- the only thing is that I had the idle issue prior to the AOS problem.

FYI-my car is a 99 c2 manual- basically stock.

[Loren]

This is a fairly common problem. You can find many similar posts here.

I would start by cleaning the throttle body and idle control valve.

[coreychan]

Also check the air mass sensor. In the durametric software. You can select air mass sensor and rpm, and monitor them. See if the sensor signal stable during idle. Since faulty air mass sensor doesn't necessary generate fault code (Only short circuit or sensor signal badly out of range generate fault code).

[wvicary]

Also check the vacuum piping after the secondary air control solenoid. It can easily break and the vacuum leak will only be present when the ECU demands the secondary air to be activated. It's located under the intake runner in the same area of the AOS so it might have been damaged during replacement.

[tornik550]

I will check with MAF sensor with durametric. My throttle body and ICV are spotless.

Considering that I do have a extra secondary air injection valve- would it be worthwhile to replace it too see what happens? Also, would I possibly get these types of symptoms if I have the vacuum hoses hooked up wrong? I will also check to make sure that all the vacuum hoses are still hooked up and didn't come undone.

Bottomline- Can a problem with the secondary air injection system (either valve, hoses...) cause a car to idle slightly rough?

[wvicary]

Yes. It could cause a intermittent poor idle.