dwightolson

Thanks much. I was able to fish a wrench back to check the tightness of the bands around the big rubber collars on the top of the engine. Seemed a little loose but tightening them didn't seem to change the frequency of the problem. I also wiggled the black plastic vacuum tubing connections that are accessible while it was surging and it didn't stop it. Does the computer monitor all the potentially related circuits for intermittent sensors or wiring? Since the surging is intermittent with the engine hot, I'm wondering if it's still some electrical bug. Thanks everyone, for any further thoughts or ideas you might have.

Thanks all of you for the ideas. I'm not sure how to check for an intake vacuum leak other than sight and sound but I don't see anything suspicious. The intake boot has been off a few times to clean the throttle body and it is tight at the moment. Is there a spray or something that I can use on the various suspect spots that might help find an intake leak? Also, I thought of maybe trying to mark the throttle stop screw setting and then trying to adjust it some each way to see if that helps. My thinking was that maybe nudging the throttle open mechanically about 50-100 rpm might keep the computer from trying to compensate. Or vice versa, closing the throttle further by backing the stop screw out a bit. Can I get in any trouble doing that and driving the car some to test the new settings, as long as I mark it first so I can get back to the factory setting? thanks Dwight

Thanks, I'll check it out. That code showed up in a computer check I had done about 3 weeks after I changed the MAS, so I wonder if I triggered that fault when I changed the MAS. A few days before I changed it, I disconnected the MAS for a couple minutes at another member's suggestion to see if it changed the idle problem.

Specialized ECU Repair (ECU Doctors) helped me out. Got me a rebuilt ECU for testing purposes. Unfortunately it didn't fix the problem. However, they are great and very helpful. I'd highly recommend them for a repair/rebuilt ECU service.

I've posted a couple times previously about the idle speed oscillating/surging intermittently when engine warmed up on my 1999 996 Cab. Intermittently at a stop sign revs up and down between 500-1200 rpm with AC off. Have now tried the ECU in addition to the throttle position switch, idle control valve and mass airflow sensor with no luck. The dealer and Porsche tech support are stumped. Only one time out of several was there any fault code - it was code 124 intake air temp sensor sporatic. The tech said that code was unrelated and that nothing was wrong. I'm grabbing at straws - is the intake air tem sensor something that is easily replaced and not too expensive? Any other ideas are very much appreciated. I hate to live with the problem. Thanks!! Dwight

Thanks again everyone. Well, tried reprogramming the ECU today. After driving it a little while, the idle oscillation came back again, intermittently. Was worth a try though - only $150. I had also unplugged and replugged in the ECU connector before that was done - everything looked clean. So I'm back wondering if it's worth a $1000-2000 gamble to replace the ECU. There is not much in that specific circuit that hasn't been replaced but maybe we are looking at the wrong place. Would an intermittent temp sensor cause something like that? But if so, would it throw a fault code if it did - I don't get fault codes. thanks Dwight

That's funny. I was talking to Jose (the doctor himself) in person yesterday at a local indie. (I'm in SoFla.) Jose is reputable. He does indeed provide a brand new unused box. He is experienced, knowledgeable and used by a couple of the indies here - including the one I regard as the best. He has done work for me, including providing a new box, and repairing an old one. The drawback to Jose is he does not have access to PIWIS or PST2, nor does he have deep contacts into Porsche. Both he and the local indies explained what he does - I don't completely understand it, and I may not have this right, but it goes something like this: He takes your old box, and sucks the software and its "configuration" out of it, and then applies it to the new box. He also applies your VIN. If all goes right, it is simple plug and play. The drawback is if there is something wrong in your old box software, and/or you have some sort of special factory mapping, and the "transfer" does not go right, he can't really help you. He doesn't actually program the box with a PST2 or PIWIS. This happened to me. My 986S is the 550 spyder version and has a mapping called something like spyder X50. When the transfer did not work correctly for reasons neither Jose nor the indie understood, the indie took over, got pass code info on my car direct from Porsche, and he and Jose together got it right. So, what does all this mean? If you have a straight 996 the chances are quite good that what you get back from Jose will be perfect. Note he also provides a warranty. If you are local OR think there is the chance that you have special factory mapping, you can mitigate the limited risk by going to Jose through the shop I went through. You end up paying Jose, and the shop, because the shop adds the PIWIS and the contacts into Porsche to figure out anything weird. Bottomline - based on my experience and the commentary from the local guys, if I had a straight 996, I'd use him. PM me if you want more of the gory detail. Thanks very much for the advice. I'm still struggling to decide whether to take the plunge for an ECU without knowing for sure if it will fix the problem. Very helpful to have this reference about Jose. thanks Dwight

Thank you, Loren. Unless I heard wrong I thought the Svc Manager said $2700 for the ECU but they may have put their programming and install labor on top of that - don't know. You might recall that you've helped me work this problem over the past two years. The idle speed oscillates up and down (about 500-1400 rpm) with the engine warm and AC switch off, about 25% of the time. With AC switch on, no surging but idle elevates to about 1400 rpm and seems to mostly stay there. With your help and the dealer we've tried the TPS, ICV and MAS with no luck. This last time the dealer asked to have it for a couple weeks and they'd interact with Porsche on it to figure it out. They said they worked with two Porsche product engineers on it. They thought it was the TPS so they got the lastest redesigned one in from Germany and it didn't fix it. Then they indicated Porsche guessed it was the ECU but wasn't sure. I really think the tech, a 30+ year Porsche tech is honest and I watched him do some of the tests one time. He said something like when it goes into the idle oscillation mode the tester shows it is thinking the throttle is 10% open but it really isn't. He doesn't think it's the wiring to and from the TPS but has only visually inspected both connectors. So, kind of frustrating, just changing parts but no fix. If I buy an ECU from Sunset, can they program it without the car so I can just plug it in and drive when I replace it? I assume I just take out the carpet mounting screws behind the right rear seat to replace it - any tricks to that? Any other ideas I might try before I decide whether to spend $1000-2000 to try an ECU? Thanks very much again for any further ideas or guidance you have. Dwight

Does anyone know anything about an ECU repair shop in Ft Lauderdale called ecudoctors.com? After several dealer visits and replacement parts, Porsche thinks my idle surge problem may be the ECU, but I'm not willing to spend $3000 to try it (non-returnable). ECUdoctors says they can exchange mine for a rebuilt for $950. They also said they are getting some new ones in from Germany this week and will offer those for the same exchange price. I would appreciate anyone's experience and thoughts about this shop or any others. Or about rebuilding/repairing ECUs in general Thanks! Dwight

Thanks again, Loren. I unplugged the MAS and it seemed a little different but not much - the idle seemed to come down more slowly and kind of hang around 1000 rpm for a bit. So, I replaced the MAS. Then I did the one minute on and ten seconds off routine to reset the computer. Didn't fix the problem. So, I'm kind of at a loss again since I've replaced the throttle position switch, the idle speed control and now the MAS. Would appreciate any other recommendations you might have. thank you much Dwight

I've had an idle speed problem since I bought my 1999 C2 two years ago. The idle speed oscillates between about 500 and 1000 rpm with the AC off. What complicates matters is that it only does it about 25% of the time. It will do it at one stop light and not at the very next for example. Doesn't seem to have to be at full operating temperature sensitive (although it's never done it right after a cold start, it has done it before it's fully warmed up). I've taken it to 2 dealers. Both the idle speed control and the throttle position switch have been replaced. The throttle body has been cleaned numerous times. The last dealer said there are no fault codes. Any other ideas would be welcome. thanks Dwight

On re-booting the computer, is it true that turning the key to the on position for at least 1 minute and then off for 10 seconds will also re-boot the computer? The workshop manual calls out that procedure for something I think it calls re-setting but I had thought (maybe mistakenly) that it meant re-booting. Can someone please clarify for me. Also, once re-booted, about how long does it take to relearn everything so I know whether it fixed the idle problem. thanks Dwight

I have a 1999 C2 Cab with 33K miles on it that has an idle oscillation problem. Only happens when warm and happens most but not all the time. The idle speed oscillates up and down between about 500 and 1200 rpms (with the A/C off). I have replaced the throttle position switch, replaced the idle speed control, and have cleaned the throttle body and none of these fixed or seemed to change the problem. Is there another very likely culprit I could try or should I buy a code reader and get some codes out if there are any? Would appreciate some additional help on this one. Thanks much!! Dwight

Thanks much for the advice, Loren. Yes, I have the C2. I sprayed some cleaner into the idle speed control while still mounted on the throttle body and it seemed to help some - can't tell for sure - still intermittently has the idle speed oscillation one time in my test drive. I will try to pull it off this weekend and clean more carefully. Dwight

My 1999 996 idle speed oscillates under some conditions. Also idles at either 800 or 1300 when the A/C is on. Dealer diagnosed and said the throttle valve switch was bad. They want $200 labor (2 hours) to install a new one (this is after another $200 to diagnose it). It looks like it is just 2 screws and an electrical connector to install it. May need to also take the idle speed adjuster unit off to get at it (another two screws but with a gasket). Does anyone know if there is anything more to it than just removing and replacing like I describe? Anything to mechanically adjust or electrically reset? Do I need to use a new gasket when re-installing the idle speed adjuster unit? The 2 hours concerns me some if it is really a 15 minute job but a bigger deal is that I have a 4 hour drive round trip to the dealer to get the job done -- so it takes a half day. Any information on what it takes to do the job is appreciated. I do a fair amount of my own work and will do it myself if there are no tricks to it. Thanks!! Dwight