Idle problems after throttle body cleaning

[Aphotodog]

I am a new member after purchasing a 2000 Boxster S with 135,500 miles. I had the CEL come on and took it to AutoZone to find the codes. They were P0507 idle air control system RPM higher than expected, P1128 02S range 2 cyl. 1-3, P1130 range 2 cyl. 4-6, P1126 O2S sensing range 1 cyl. 4-6. A friend told me to check for vacuum leaks. I found the tube fron the air cleaner was not attached. I pulled the TB and using throttle body cleaner. It was pretty dirty having air coming straight into it with no filter. I also cleaned the MAF with CRC's product. I took out and cleaned the K&N filter that a previous owner installed after removing the stock air filter and housin (darn it). Reassembled it all, turned the key to on and waited a full minute, turned switch to off, waited 10 secs and cranked it up. Seemed fine while it idled. CEL was still on. I took a shower then cranked it up to run 5 miles to the grocery. There is a knocking and unstable idle. It runs strong when above 2000 rpm. Pull up to a stop, idle drops to 700 and seems like about to stall. Thing was running great before I did all this but was idling at about 1100 rpm. I disconnected the battery to clear CEL which is now off. Still pulsing idle and knocking when I fired it back up. What have I done wrong? Thanks for any advice.

[particlewave]

I'd start with the throttle body and idle control valve. Inspect the TB and replace the ICV.

[Aphotodog]

At over $200 for a part that is unlikely returnable, I wonder how I can verify that is the part failing. I appreciate your reply. That is a part the codes imply is suspect.

[particlewave]

Well, the code is a clue.

Try a used one from Woody and see if it changes the behavior or cures it. The cost will probably be a lot less than new.

[ndfrigi]

I think when you clean a trottle body, the flap will change its position that will make some changes on your idle. Your computer I think has to adjust to the new airflow/vacuum after cleaning the trottle. what happen now, the flop will close more than when it was dirty after thousand of miles running.
The computer was adjusted little by little on how the vacuum/air flow.
Did you try removing your battery so the computer will also reset and adjust itself base on how the air flow now on your trottle or vacuum lines.

[Aphotodog]

I really looked it over this morning. Squeezed my fingers under the rubber boots on each side of the plenum. Sure enough I had failed to get them fully seated. Removed and reinstalled correcting my error. Fired it up and smooth idle at 700 rpm. The CEL has stayed off. Took it for a test ride and all is smooth, no stutter or stall. I'm very happy. I need good jackstands for what a ICV would cost. Thanks for the replies.

[Dave2001S]

Just chiming in here. I have the exact same problem, and I mean exact, with one exception: I'm not getting a CEL. At low RPMs it hesitates and wants to stall. After warming up it seems to do fine. I removed and cleaned the air filter, throttle body and MAF sensor as you did. I can also feel occasional slight hesitation at higher RPMs during freeway driving. Checked my connections around the throttle body and everything seems to be tight. I'm going to replace the MAF sensor and see if that cures it. But I have one question for anyone who can help. When I reconnected the hard plastic air intake tube to the throttle body I noticed there was a thin O-ring that seemed to fit around the neck of the throttle body. With that O-ring in place I absolutely could not get the intake tube properly seated. Further, the O-ring didn't really fit around the throttle body snugly, but rather loosely, so I was confused as to its functionality. After more than an hour of trying to slip the intake tube back onto the throttle body neck with the O-ring in-place, I ditched it and tightened the clamp down extra securely. It seems to fit properly and doesn't move at all. However......as the problem is still with me, I'm suspicious of a vacuum leak I cannot see, or maybe that O-ring is critical and I should have it installed right. Anyone familiar with this?

[911monty]

Originally Posted by Dave2001S

Just chiming in here. I have the exact same problem, and I mean exact, with one exception: I'm not getting a CEL. At low RPMs it hesitates and wants to stall. After warming up it seems to do fine. I removed and cleaned the air filter, throttle body and MAF sensor as you did. I can also feel occasional slight hesitation at higher RPMs during freeway driving. Checked my connections around the throttle body and everything seems to be tight. I'm going to replace the MAF sensor and see if that cures it. But I have one question for anyone who can help. When I reconnected the hard plastic air intake tube to the throttle body I noticed there was a thin O-ring that seemed to fit around the neck of the throttle body. With that O-ring in place I absolutely could not get the intake tube properly seated. Further, the O-ring didn't really fit around the throttle body snugly, but rather loosely, so I was confused as to its functionality. After more than an hour of trying to slip the intake tube back onto the throttle body neck with the O-ring in-place, I ditched it and tightened the clamp down extra securely. It seems to fit properly and doesn't move at all. However......as the problem is still with me, I'm suspicious of a vacuum leak I cannot see, or maybe that O-ring is critical and I should have it installed right. Anyone familiar with this?

Are you sure this O-ring is not the one that is supposed to be installed between the throttle body and the manifold? Could explain a leak.

[Dave2001S]

Yes, its called the throttle body seal gasket. It has a small tab on one side. And I agree, omitting it could explain a vacuum leak. However, I just simply couldn't get the intake tube back on with that thing in place. I wonder, should this gasket fit snugly onto the slot of the throttle body, sorta like a rubber band? The one I ordered fits loosely and therefore gets tweaked and pushed out of the way when I slide the air intake tube back.

[Dave2001S]

I meant to mention also, I have looked at several videos on YouTube showing the process of removing and replacing the throttle body, and in no case have I noticed one of those gasket seals in-place. I remain mystified as to the functionality of this gasket, although I would understand if it fit better and allowed the air intake tube to reattach.

[Aphotodog]

I never found an 'O' ring as you described when dismantling mine, but I'm like the 4th owner. However, mine is running well now but the CEL has popped on again. I'm gonna have the code diagnosed again. If it is O2 sensor related again, I'm gonna pull them and soak them overnight in gas, dry them out and reinstall. If there was an O ring involved in mine when new, it's not in the game anymore.

[Dave2001S]

Thanks, appreciate knowing that. Odd that our problem seems identical, and I'm not getting the CEL whereas you are.

[Dave2001S]

A bit of a delayed follow-up here but I hope you can help me. I'm still having persistent stalling problems with my boxster. I am wondering about the idle control valve, but I am a bit confused. Does the throttle body on my 2001S even have one of those? Or is it electronic?

[edc]

There is no separate idle control valve on an S.

[Dave2001S]

Thanks, appreciate the reply! I guess I can eliminate that as the culprit then!