997.1 C4S High Idle / Low Acceleration

[stphnsns]

Hi guys, I always appreciate the helpful information I get here, so I thought I'd throw out my latest issue, and see if anyone had any input or advice. I have a 2006 997.1 C4S coupe, with approx 75k miles. I've owned the car for two, essentially trouble free years. I've sensed for a while now that I might be eventually facing the alternator cable update coming, as she's become a little slow to crank, and definitely slower when warm. But the car has always started, and then run great. I recently had an oil anaysis at Blackstone, and everything checked out well. Anyway, over the weekend, when I went to start the car, it was a little slower cranking than usual, but did start. After this, and ever since, it has been idling high - at 1,100-1,200, seemingly getting higher as the car gets warmer, and acceleration is at - I'd estimate, only 50-60% or so. Actually feels more like my 2.7 Boxster (way off, but seemingly more than limp mode). There is no CEL, and no codes. As per advice given to guys here on previous threads, I cleaned the throttle body (which looked pretty good to start with), as well as the MAF (ditto). No change in performance. So...my question is...could this performance change possibly be related to the alternator cable issue? Could the related voltage change cause these issues? If not, does anyone have any other suggestions of where to look? Plugs were done a year, and approximately 3,00 miles ago (I know, I need to drive it more), and coils were stated to be in good visible shape at that time. Thank you, as always, for any valuable input you can provide!!  

[JFP in PA]

If the voltage is not where it is supposed to be, all sorts of problems can result.

 

The very first thing to check is the voltage drop across the battery cables; these are well known for developing internal corrosion that causes this exact problem.

[stphnsns]

Thank you JFP, will plan to check that ASAP! 

[stphnsns]

Hi, my mechanic just checked the voltage, and noted everything is good, and consistent. Would anyone have any further suggestions to this mystery? It's difficult to trace with no CEL. Thanks in advance! 

[timbo]

how old is the battery?

 

[stphnsns]

Hi, thanks for the post. The battery is, I believe, approx 2 yrs old. Voltage is strong and consistent from the battery, and also to the alternator. Interestingly, we kind of think we have it narrowed down (hopefully!) to a bad throttle body. Others have posted of similar issues. So we just replaced the throttle body, and got full power back (& also eliminated "sport mode failure" message which had started illuminating), but now the idle is VERY erractic, the car is harder starting. Unfortunately, for some reason, the OEM throttle body I ordered didn't come with a new seal, so I am now ordering a seal, and hoping this will take care of the idle - and all problems. I will report back. Anyone please feel free to chime in, if they have any input or advice! Thanks again for all. 

[stphnsns]

So, in case anyone runs into a similar problem, it turns out the problem was indeed the throttle body, in this case. It may have actually been the (attached) sensor, as the throttle body itself seemed ok. Once the DME "learned" the new T.B., everything has been great, and the car is back to running like new. I hope this helps, if anyone else encounters a similar problem. 

[Loren]

31 minutes ago, stphnsns said:

So, in case anyone runs into a similar problem, it turns out the problem was indeed the throttle body, in this case. It may have actually been the (attached) sensor, as the throttle body itself seemed ok. Once the DME "learned" the new T.B., everything has been great, and the car is back to running like new. I hope this helps, if anyone else encounters a similar problem. 

 

[stphnsns]

I am unfortunately reviving this (exactly!) year old thread, started by me, as the symptoms I described above have mysteriously returned. Essentially: Higher than normal idle (1200-1500: goes up as car warms up), lack of power upon acceleration (probably 50-60%), and failure of sport mode to activate. Those are the primary symptoms. We replaced the throttle body, and thought that did the trick (seemed to for a while). Also in the last year, we've replaced the water pump, AOS, and drivebelt. My lucky year! Anyway, after about 3,000 miles, the problem has returned. It did a couple months ago, but after disconnecting the battery, it self corrected - for a time. Now its back and nothing I do seems to help. I removed the MAF completely, and the idle drops down to normal-ish, but there is ZERO acceleration. I assume that tells me the MAF is good? My other hint is from Borrowed knockoff Durametric software, I got the following readings (there has been NO CE light through any of this, and yes, the CE light bulb works)

 

Codes:

P1514 - FACTORY FAULT CODE 540 - THROTTLE JACKING UNIT LOWER MECHANICAL STOP

P1511 - FACTORY FAULT CODE 543

P2126 - THROTTLE ADJUSTING UNIT - POTENTIOMETER 2

P2121 - THROTTLE ADJUSTING UNIT - POTENTIOMETER 1

P1517 - THROTTLE JACKING UNIT ABORTION OF TEST

 

I believe that test was while running. When tested not running, the only readout was P1514. 

 

So, since the throttle body is new, I am wondering if it could be the other throttle position sensor - the gas pedal. Would love to hear if anyone has any insight or related experiences. THANK YOU!