Rough Running 986

[Lee Timmer]

986 Boxster MY99 55K miles

Hello. I'm having some idle and rough-running issues. As my car is sitting in traffic, the idle fluctuates just a bit between 800-1000 rpm. Not a big deal as far as I know. Might it be a dirty throttle body? I recently had a tuneup completed: new plugs, filters, etc. I also recently added Red Line's fuel system cleaner and since then, my car seems as though it doesn't run as well as before. I've heard others say it's a good idea to change your oil soon after adding cleaner, but my mechanic said that it's unnecessary. I just find it odd that the car runs worse AFTER adding the cleaner.

Finally - and please pardon my ignorance - I also have a bottle of Swepco 503 cleaner. Would it be unnecessary - or even dangerous - to add that as well, considering that I just added the Red Line? I've been trying to educated myself as much as possible about my new toy, but I obviously have a long way to go. Many thanks for any suggestions.

[1schoir]

Lee:

From the symptoms you describe, it sounds like there are either gum deposits or dirt interfering with the proper operation and movement of the idle control valve and of the butterfly valve inside the throttle body.

It would be a good idea to remove and clean your throttle body and to do the same with the idle control valve on your '99.

Here is a detailed DIY on how to do both: http://pedrosgarage....ottle_Body.html

Regards, Maurice.

Edited June 23, 2012 by 1schoir

[Lee Timmer]

Lee:

From the symptoms you describe, it sounds like there are either gum deposits or dirt interfering with the proper operation and movement of the idle control valve and of the butterfly valve inside the throttle body.

It would be a good idea to remove and clean your throttle body and to do the same with the idle control valve on your '99.

Here is a detailed DIY on how to do both: http://pedrosgarage....ottle_Body.html

Regards, Maurice.

Thank you. I'm actually planning to take it to my mechanic next week to have him look at the throttle body. I'd do it myself but I'm not mechanically inclined. What about mixing the Swepco with the Red Line? Any thoughts on that? Thank you so much, Maurice.

[fingal]

Thank you. I'm actually planning to take it to my mechanic next week to have him look at the throttle body. I'd do it myself but I'm not mechanically inclined. What about mixing the Swepco with the Red Line? Any thoughts on that? Thank you so much, Maurice.

Take it for a proper rip and 'burn the carbon' out of it. Add the swepco to the next tank.

[mikefocke]

I assume you added the cleaner to an almost full tank of gas. So you already have gas with cleaner in it even beyond the cleaner the gas comes out of the pump with. So I'd wait on adding any other cleaner until you have burned that tank of gas.

And how is your AOS? The throttle body cleaning will tell you about the AOS condition.

[Lee Timmer]

I assume you added the cleaner to an almost full tank of gas. So you already have gas with cleaner in it even beyond the cleaner the gas comes out of the pump with. So I'd wait on adding any other cleaner until you have burned that tank of gas.

And how is your AOS? The throttle body cleaning will tell you about the AOS condition.

I’m close to using up that first tank. I had the throttle body cleaned and the idle fluctuation seems to be a little better, but it’s still noticeable. As for the AOS, I’m able to remove the oil cap while the engine’s running with no problem (I’ve heard that’s a good thing). I’m still learning. I’ll actually be taking the car to a retired Porsche mechanic in a few weeks for my 60K service. I have a list of other things ready, believe me. Thanks for all the advice.

[bar10dah]

Does the idle appear to slowly climb to 1,000, then drop off back down to 800, just to start it's slow climb back up again?

[Lee Timmer]

I assume you added the cleaner to an almost full tank of gas. So you already have gas with cleaner in it even beyond the cleaner the gas comes out of the pump with. So I'd wait on adding any other cleaner until you have burned that tank of gas.

And how is your AOS? The throttle body cleaning will tell you about the AOS condition.

The other day, while the car was running, I took the oil cap off. It was easy to remove, but the car sounded like it wanted to die. It didn't, but it was close. AOS issue, maybe?

Edited July 12, 2012 by Lee Timmer

[mikefocke]

The AOS is easy to diagnose based on the amount of oil it would dump into the intake and onto the throttle body if it fails.

The AOS is plastic and 12-13 years old....

[Lee Timmer]

The AOS is easy to diagnose based on the amount of oil it would dump into the intake and onto the throttle body if it fails.

The AOS is plastic and 12-13 years old....

Forgive me, but I have autism and sometimes don't understand things clearly. Are you saying that you think it is an AOS issue?

[mikefocke]

Since I'm not standing with your car in front of me and instruments for measurements in my hand, all we can go on are probabilities and your description of sysmptoms.

And, concerning the AOS, it could cause problems at its age and mileage and it is easy to figure out if it is a failed AOS by removing the tube between the air cleaner and the throttle body and examining the amount of oil in it. A thin film of oil...probably not the AOS. Drops of oil and probably worth changing the AOS and J-tube.

The AOS filters oil out of the "air" within the crankcase and routes the unburnt hydrocarbons back into the air intake stream to be used in the combustion cycle again. If the AOS isn't filtering, then much more oil will get up into the intake and cover the throttle body and cause hesitation and sputtering because the throttle body can't react as well as it should because it is covered with deposits. Same thinking about the valves Maurice mentioned. Clean things react well, dirty clogged ones don't.

[JFP in PA]

If the AOS is functioning correctly, there should be a low vacuum signal at the oil fill cap, in the range of 5 inches of water. Any higher and the AOS has to be changed as it is on the way out. Most shops have a modified oil cap that connects to either a low range vacuum gauge, or a slack tube manometer for checking the AOS; the slack tube manometer is something anyone can jury rig using some clear flexible tubing and a ruler for the purpose.