Rough start, erratic idle... throttle body?

[nc986]

'02 Boxster (986), manual, 50k miles

My CEL came on one hot day a few weeks ago. Thinking it might be the old "didn't tighten the gas cap" problem, I waited for it to go away. Later, I noticed some wandering idle (600-900 RPM), but only occaisionally. Then I noticed that when it was idling smoothly (when warm) it was idling near 1000 RPM, which seemed high.

In the middle of that 2 week span, I unhooked my battery and lost all of the error codes and the CEL. The CEL has not come back on, but the other symptoms remain. On two occaisions this week, the car took 3 tries to start. On the failed attempts, the engine seemed unable to reach high enough revs to sustain momentum.

Here's what the problem isn't: new battery, new alternator, new driver side window motor, new ignition switch (all within 5k miles), clean MAF (yesterday), Porsche 40k mile service. The only thing I haven't done yet is clean the throttle body. What do you think? Waste of time or possible solution?

Side question: how in God's name do you get the air supply OFF of the throttle body? Is it safe to pry with a screwdriver? I tried by hand and could only pivot it a degree or so. Side question 2: how do I get to the friggin' screws under the throttle body? Is there a trick, or do I just have to be persistant with an allen wrench and take my frustrations out on an inanimate object?

Please help.

- Chris

[vizcarra44]

'02 Boxster (986), manual, 50k miles

My CEL came on one hot day a few weeks ago. Thinking it might be the old "didn't tighten the gas cap" problem, I waited for it to go away. Later, I noticed some wandering idle (600-900 RPM), but only occaisionally. Then I noticed that when it was idling smoothly (when warm) it was idling near 1000 RPM, which seemed high.

In the middle of that 2 week span, I unhooked my battery and lost all of the error codes and the CEL. The CEL has not come back on, but the other symptoms remain. On two occaisions this week, the car took 3 tries to start. On the failed attempts, the engine seemed unable to reach high enough revs to sustain momentum.

Here's what the problem isn't: new battery, new alternator, new driver side window motor, new ignition switch (all within 5k miles), clean MAF (yesterday), Porsche 40k mile service. The only thing I haven't done yet is clean the throttle body. What do you think? Waste of time or possible solution?

Side question: how in God's name do you get the air supply OFF of the throttle body? Is it safe to pry with a screwdriver? I tried by hand and could only pivot it a degree or so. Side question 2: how do I get to the friggin' screws under the throttle body? Is there a trick, or do I just have to be persistant with an allen wrench and take my frustrations out on an inanimate object?

Please help.

- Chris

Hello Chris,

I am a former Porsche tech and I never saw a dirty t-bdy cause a check engine light, now the wandering idle yes. I would look at the dme data to see how the

Rkat fuel trim looks as well as the Lambda values and Maf value. It gets expensive guessing I imagine. I am a firm believer in proper diagnosis, not just parts replacement, so when people start to tell you it might be this or that, take that advise at your own risk. Now for the air duct to come off, I just used a twist and

pull at an angle step, with a little umpff. to get the clamp loose, I used to use a swivel 1/4 ratchet with i believe a 7 or 8 mm socket.

regards,

vizcarra44

[nc986]

Thanks vizcarra44,

I really appreciate the input. Could I be dealing with 2 problems? Maybe the MAF caused the CEL, and the throttle body is causing the idle/starting issue? I'm grasping at straws. I usually ascribe to the "simplest explanation is best" philosophy, so it pains me to even ask that question.

Can I draw any conclusions from the fact that the CEL has not come back on in the 50 miles and 5-10 trips since I disconnected the battery? Will the computer record error codes even if the CEL is not on? In short, if I take the car to a mechanic at this point, are they going to read the computer and get nothing out of it (except my $50)?

Come to think of it: if my car has failed to start twice, and the idle is rough or high, why ISN'T my CEL on? A clue, a red herring, a coincidence...

- Chris

[4agdtym]

In short, if I take the car to a mechanic at this point, are they going to read the computer and get nothing out of it (except my $50)?

I have heard that you can go to your local auto parts house (kragen, autozone, etc) and borrow their code reader if they think you'll buy needed parts from them. That will at least save the money if there are no codes.

David

[vizcarra44]

In short, if I take the car to a mechanic at this point, are they going to read the computer and get nothing out of it (except my $50)?

I have heard that you can go to your local auto parts house (kragen, autozone, etc) and borrow their code reader if they think you'll buy needed parts from them. That will at least save the money if there are no codes.

David

I never had a bad Maf cause a no start, but you never know huh. With a good Obd scanner you should be able to see if there are any pending codes, that have not matured yet. Also, when your cranking the car and its not starting, usually a code will not set due to the fact that certian systems need to be within particular thresholds to have the ecu monitor systems for problems. When using a basic scanner just look at the short and long term fuel trim, anything above

8% negative or positive is a problem. There are many different diag strategies for no code problems. You just have to find a tech who likes to troubleshoot.

Regards,

vizcarra44

[nc986]

- I had the starting problem first last Tuesday. Not every start, just once.

- Yesterday I cleaned the MAF, and had no start problems before or after.

- Today, it took 3 tries to start the first time and I didn't crank it again.

I've done all I can to the MAF with apparently no effect on the starting issue (or idle issue for that matter). This doesn't really absolve the MAF of responsibility, but I'm on to the next DIY step before I go to a shop.

I'll take the car over to Advance Auto Parts and see if I can get them to read whatever codes they can. My last trip, they told me they'd only check it if the CEL was on, so I'll have to beg a little. Wish me luck.

If I get some results out of the codes, I'll move forward accordingly. If I don't get anything out of it, I'll see if cleaning the throttle body has any effect (once the codes have been read, I figure unhooking the battery again won't lose me anything).

I'll check this board again tomorrow, so any other input would still be appreciated. If I get any new data, or a resolution, I'll be sure and let y'all know.

Thanks,

Chris

[Chris_in_NH]

this sounds like it might be a failed Air-Oil Separator (AOS or A/OS).

you can check inside the throttle body to see if there's more than a misting of oil. mine had a ton of oil in it when my A/OS went bad. here's a pic.

there are 4 bolts that hold the throttle body to the intake plenum. one of them (the lower one on the passenger side) is notoriously hard to get at. you need a socket extension to get in there, and you may need to remove a small aluminum support bracket, depending on the size of your socket extension. you'll know which one i mean when you can't get a straight line to the bolt with the socket extension. the bracket is removed easily if you do need to remove it, it's just a pain in the butt.

there is also another bolt on the bottom of the throttle body that you'll need to remove if you want to completely remove the TB. but i just unscrewed the 4 main bolts so i could peek inside. there was enough room so i could also clean out the TB.

so as a first step, check your TB for oil. if there's oil, then the A/OS is bad and will need to be replaced. if there's a lot of oil in the TB, i would not drive the car until the A/OS is replaced. if the engine eats too much oil, one or more of the cylinders could fill with oil and since oil can't be compressed, something has to give. your engine! :unsure:

the problem could also be a bad MAF. i cleaned mine and it was fine for a while, but eventually it went completely bad (and i had the same symptoms you are having). you can check to see if it's the MAF by disconnecting the MAF's wiring harness (leave the MAF in place), then reset the DME/ECU (do not skip this step!) by disconnecting the negative battery cable for at least a minute (have your radio code handy if your radio needs one) and then re-connect the neg cable. if the car starts normally/runs normally, etc., then the MAF is bad. you will not do any damage to your car by running it without the MAF.

let us know what happens...