rmc1148

I hear you and I do 95% of my own work but if I replaced everything that you have and my car still stumbled I would have it diagnosed. I commend you for the effort believe me.

"02996ttx50

between your obvious knowledge of the inner workings of cars in general, your having "read up" on them, tripled with your being able to reach out to umw/kevin is more than half the "battle" lol. my math isn't quite right lol. but you've got it sorted i'm sure

me, i had to learn all of "it" from scratch! the dollars involved forced me to become the avid and devoted student of "them" that i am today

up4speed

Thanks again to everyone's help and responses. I'm truly appreciative of any info that I can pick up along the way.
Next step is going to be the wideband O2 sensors. I don't have any receipts stating that they were ever changed prior to my ownership, so that would make them approximately 14 years old. At best, I'll consider them "weakened". That should hopefully take care of the last remaining issue with the car. I'll also probably benefit from a little better mileage by replacing them. If not, I just bought myself another 10 years with those sensors, LOL.
By the way, if anyone has any tips or tricks to replace them, I'm all ears. It appears to me that it should be straight forward:
- remove air box
- unjack and remove wire from clips
- unscrew sensor and replace
However, I worked on this 911 enough now to know that the simplest jobs are a pain! I can't believe how tough some things are to do due to the limited clearance.
I should have the O2 sensors installed within a week...I'll post back with results!

rmc1148

I'm sure you mentioned it but how many miles are on the car?

up4speed

The car has only about 19,200 miles.

By the way, I just used it again today. I have to admit, it seems 10X better than before I did any of the above work, and it runs ridiculously strong and smooth (once warmed up). It is smoother, pulls harder, shift to 1st is seamless when I down shift, and no surge in 3rd to 4th gear under light throttle.
It runs so good that I'm second guessing my last 2 problems. I'm thinking that they may be "normal".
The lumpy idle when engine is started cold is very consistent. It's a 50/50 split on the forums on whether it's normal or not. I'm going to change the O2 sensors as I said just for good measure, but I think that it may even fix the issue if it's not normal. I'm anxious to find out.
And, lastly the sound that I heard and perceived as detonation may actually be just a rattle. I tried to duplicate it today, while I very carefully tried to listen to the sound quality and its source. It took me a while, but I was able to duplicate it a little today. I can't duplicate it on demand, but I got it to make two rattle ticks (like a one two punch). I'm suspicious that it can possibly be the actuator rod on the turbo. I realized when it was on the lift that the actuator rod on the drivers side has a tiny amount of play, so when I tap on it, it makes a rattle/jingle. Also, both times it made the noise (that I heard) I was on the throttle at least 3/4 and once the boost built, that's the point that I heard the sound. I'm thinking that maybe it's the point that it activates the waste gate, hence the noise. Is that possible or common?

rmc1148

A for effort. Nice to hear its running strong.

up4speed

I am in the process of changing the plugs and wideband O2 sensors. Do I dare say that it's actually FUN? I may be a little twisted sometimes, LOL
So far everything went smoothly except for the fact that I snapped off the locking clip on one of the coil pack connectors. Be careful of these, they probably get brittle from heat cycling and age.
The worst part is that my production came to a halt until I get a replacement connector. Thankfully I have a friend that may have an old harness lying around and he may be able to give it to me tomorrow so I don't get delayed a few days waiting for it to come in the mail.
The interesting part is that EVERY SINGLE plug was loose! Most were removed with light wrist pressure. The color of the plugs were all a nice light brown color, but the threads looked like they had a heavy grease on them. I'm not sure if that was anti-seize used by prior mechanic, or if it was just accumulation from blow by on the loose plugs. I think that the mistake that the prior mechanic made was to torque the plugs only once. A lot of people don't realize that the o-ring compresses and the plug will loosen up if it is not re-torqued a few times. I did them at least 3 times each with a few minutes in between each time. Hopefully that will prevent them from loosening in the future.
I have a good feeling that the loose plugs may have causes the idle issues that I'm having, and maybe even the sound of a misfire under load. I'm not having a good feeling about the misfire sound because I'm thinking that it may just be a rattle since there is no code or loss of power or drivability when it does the noise. In addition, it was very random and I was not always able to duplicate, so I will cross my fingers on this. I also checked the brackets near the middle plugs just in case they are ready to fail, but they looked brand new (very low miles on the car).
At this point, I'm VERY anxious to road test her to see if there is a difference.
It should be ok to start the car before I install the bumper (after everything else), just to make sure that it is ok, right? I would hate to have made a simple mistake forgetting something, just to find out after EVERYTHING is all back together! I'm sure that I did everything correctly, but I'm human so you never know.
Oh, one more question. Do you guys think that I should disconnect the battery to reset the computer to accept the new plug and O2 sensor parameters, or does it not matter?

rmc1148

Nice garage. You do not have to disconnect the battery after doing tune up. Never heard of retightening plugs numerous times? but who knows I have never had them loosen over time. Hope you get it running to your expectations as god knows you have replaced about everything.

"02996ttx50

not necessary to reset battery or anything other than codes with a durmateric if you have any pending/active when changing out the 02's. just did this thursday meself

up4speed

Thanks for the compliment!
Yeah, I agree. I pretty much changed everything that I would reasonably be capable of, lol. Actually, the only thing I didn't change was the coils. I inspected them VERY carefully and they looked perfect, plus the car has low mileage, so I would be shocked if there was a problem.
I'm also hoping that it runs 100% perfect when I'm done. I will definitely update the thread with the results. All my problems were VERY subtle, but I'm very sensitive to what a proper running car should feel and sound like (of course there are always those weird characteristic things that are unique to each car. That's why these forums are great. For instance the marbles at idle on the 996 turbo)

Thanks for the info. I never had any codes or even pending codes on my car since I've owned it. How did you do the O2 sensors? Did you work around everything, or did you also take everything apart for easy access?

rmc1148

My car has 13k and coils look new so agree there is no benefit to replacing but some people have contrary opinions lol. These motors do have their distinct sound at start up but overall its a wonderful mechanical noise they produce and I love it.

up4speed

I changed my mind about the coils. After hearing all the facts and speaking with Kevin at UMW, I decided to replace them since all of the labor is already done. They are the original 996 coils that are bound to eventually fail, so the 997 updated coils sounded like a good idea.
I should have it all together by the end of this week (hopefully). I'm anxious to see the result. I will definitely update with the results.
Keeping fingers crossed

up4speed

It's all back together. I have to admit, it is a very easy job. If you are handy and are considering doing the plugs and coils by yourself, don't be afraid. There is nothing hard about it. It definitely takes a long time the first time, but it's not hard.
As far as the results of my work, it's hard to be 100% sure until I get a little more time with it. As of now, I felt like it idles smoother overall, but it still does that whole dip in the RPM's after 3 seconds, then hunts a little for the idle (visible on the tach, not enough to hear anything). Even though it does the same routine that it used to, it feels smoother during that time. I feel like it went from feeling abnormal to something that generally feels normal.
I also haven't heard that rattle sound under engine load that sounded like detonation. I tried giving heavy throttle several times and it just pulls very hard and smooth and doesn't make that noise. I'll have to assume it's fixed unless I hear it again. It also hasn't done that slight surging either.
I'm guessing that the rattling noise was caused by loose spark plugs, and the surging was caused by the leaking v-pipe. Since I did the spark plugs, coils, O2 sensors, MAP sensor, MAF sensor and I still have that dip in RPM's when started cold, I'm going to have to assume that it's a normal characteristic. Especially since it runs great and idles rock solid when warmed up.
If something changes, I will post back, but I will assume that everything is fixed for now.
I want to also thank everyone that chipped in to help me with diagnosing and fixing my car. I appreciate all the time you guys took out to help me!
I also wanted to give a special thanks to Kevin from Ultimate Motorwerks (UMW). He went above and beyond to help me out and his troubleshooting is always spot on, which is truly amazing when the car is thousands of miles away from him!!
Speaking of Kevin at UMW, I have an UMW performance tune on my car and during this whole troubleshooting episode, I went back to stock tune. I can not believe how much slower the car is when stock! The only mod to my car was his tune, and it is a NIGHT and DAY difference in torque and power. I would have never imagined that it would even be possible to make that difference. In all fairness, I don't have experience with turbo cars, and I guess it is probably easier to squeeze power out of a turbo rather than a normally aspirated engine. I'm so impressed with the tune that I'm going to start a new thread letting people know how I feel about it.

dprantl

A dip in RPM 3 seconds after a cold start. This sounds like the A/C compressor engaging. The ECU is supposed to compensate for the additional load that the compressor puts on the engine at idle, so it raises the idle RPM by a set amount right as (or a few milliseconds before) the compressor turns on. One possible explanation is that the compressor is getting old and provides more resistance than a new one, causing the ECU's initial idle compensation to be insufficient. After a brief period, other ECU compensation methods will correct the idle.

Next time you start the engine when cold, immediately press the A/C compressor button on the climate control (the one with the snowflake) so the compressor stays off and see if the dip still occurs.

Dan

up4speed

It sounds good in theory, and it definitely feels like an engine when the compressor cycles on, but I have the climate control in the "OFF" position and it still does it. Now that it's smoother, it feels more normal. I'm wondering if its switching from closed loop to open loop when it does the quick dip in RPM's?
Also, after the dip the RPM's hunt up and down slightly (~50 rpm) until it warms up. I'm not sure at this point if it's all normal, but I'll take a video next time I start it cold.