Need help with 986 troubleshooting - rough idle, etc.

[428street]

Yes sir, thats the lesson here and I thank you for teaching/reminding me that.  I'm an IT guy by trade and I understand the troubleshooting process with everyone else's stuff except mine.  Understand neither of us have a crystal ball but does it make sense proactively to change the other two 02 sensors?  Not for age but for time seeing the car is close to 20 y/o.  When I took the PC sensor out the tip was white as a ghost.

[JFP in PA]

1 hour ago, 428street said:

Yes sir, thats the lesson here and I thank you for teaching/reminding me that.  I'm an IT guy by trade and I understand the troubleshooting process with everyone else's stuff except mine.  Understand neither of us have a crystal ball but does it make sense proactively to change the other two 02 sensors?  Not for age but for time seeing the car is close to 20 y/o.  When I took the PC sensor out the tip was white as a ghost.

 

The color is not unusual.   As a shop owner, I tend to leave things like O2 sensors alone until they tell me they have a problem.  We have customers that have gone over 200K miles on a 986 with the original units.  Others  seem to have issues earlier.  Like catalytic converters, it seems to be more related to the quality of the fuel people use than miles.  At a gathering of shop owners, a discussion of cat and sensor life’s got started, and those with shops in urban areas with stiff local fuel taxes observed that they see a lot more failures than those of us out in the sticks, leading several owners to observe that customer’s in the high fuel tax environments buy the cheapest fuel they can find, which raises  the question about the quality of those cheap fuel supplies, and what that may be doing to emissions components.  While not a scientific examination, it was an interesting observation.

[428street]

Fair enough.  I've only ever used 92/93 in the car.  For now just going to leave it and enjoy the ride.  Thanks again.

[428street]

I'm back!!!!!!!!!!!!!

 

So put about 50 miles on since last post and again, car is running amazingly well but then this happened 😞

[JFP in PA]

Start looking for air leaks on your intake and vacuum lines.

[428street]

OK.  Any pinpoint diag I can do with the Durametric I have?

[JFP in PA]

1 hour ago, 428street said:

OK.  Any pinpoint diag I can do with the Durametric I have?

 

Not really, other than confirming your fuel trims are out, which the codes have already done.  In this case a smoke test would be more useful.  Finding air leaks that throw the mixture off can be a major headache.  These are handled strictly on a “time and materials” basis in the shop; it could take 15 min., or it could take four hours.

[428street]

That was the next question I was going to ask you.  There seems to be a new Indy in my town who specializes in Porsche which I might give a shot at.  Buying a smoke machine for this one problem is probably not the best decision although it does seem cool.  I deleted the CEL and took for another drive with no new CEL but my gut tells me it's just around the corner.  I also did the oil cap test and it did change idle when I took the cap off so more than likely some kind of vacuum issue.  I might just for one last shot take the TB tubing off and put back on again as that is the only thing I touched vacuum wise but bottom line is that smoke test would tell me right away.

[crwarren11]

Considering the things you have recently done, I would check the Rubber boots around the throttle body, as well as those around the intake plenums. These are common, especially at the age of your car to tear. Also if you don’t have them properly seated between the plenum and the throttle body then they will throw these codes. It is almost certainly a vacuum leak and something that you can find with a bit of effort. I have personally ripped those rubber connectors several times, and have over tightened the clamps to create rips or leaks in the vacuum. Just look around and I’ll bet you find it. 

[428street]

Thank you sir, when I put it back on the first time (TB) it was a bear fight to get off and on so maybe I did rip one or both of those rubber sleeves...thanks for the .02...

 

[428street]

So in thinking this through I have two options.  1.  Take it to an indy with a smoke machine and just nail the problem and yes it will cost me some money but overall in 19 years of ownership I've spent very little on a 19 year average.  2.  Continue to troubleshoot on my own with everyones help.  Flip a coin.  I know I'm close...

[crwarren11]

I mean, you’ve got it there so might as well take a peek. I’ve had my TB out so many times over the past few months and I can’t tell you how many times the boots haven’t been seated correctly causing the same codes. Usually on the bottom where you can’t see that they’re actually not joining the tubes correctly.

[428street]

Yes, that is exactly where I screwed up when I initially was going in the wrong direction even after I changed the 02 sensors.  I went back in and really took a good look and found on the bottom just like you said was not right.  Loosened everything up and I thought I got a really good seal this time but maybe not.  It's VERY possible I overtightened them too.  It also could be the gasket between the TB and the plastic tubing.  Whatever it is its not horrible because like I keep saying the car is running amazingly well.  I might buy new rubber sleeves and a sealing ring for the TB and change them to rule out those as being issues.  I can and will take it apart again and inspect but at that point I have them off and all apart might as well change them after 20 years regardless.  

[Vtx531]

I have the same codes on mine. I made a pickle jar DIY smoke machine. Worked GREAT and cost about $8 including the pickles but I already had some items laying around.

 

Search youtube for instructions.

 

I made a couple modifications: Instead of bic pen I used two tire valve stems ($2/pair). Drill 1/2” holes for the valvstems and the soldering iron. Remove valve core on one of them and 1/4 hose fits on perfectly. I used $6.99 12v air compressor from harbor freight. Pickle jar I upgraded from 24oz to 32oz to have a wider lid. Use rubber glove with pinkie fingertip cut off to attach to 1/4” hose and adapt to the large intake hose by the throttle body (have to remove the hose between throttle body and MAF. I used hot glue to attach the soldering iron so I could remove it later and because it was faster/easier than epoxy.

 

I believe I found my leak is the bellows under the AOS.

 

Hard to believe but this works perfectly. I whipped it up this morning and was smoke testing within an hour. Haven’t had a chance to do the repair yet but I think I now know the problem.

Edited September 9, 2019 by Vtx531

[428street]

Wow, that is an work or art!  Good for you, I'm not sure I'm that motivated but its good to know you can make a smoker on the cheap.

[Vtx531]

10 minutes ago, 428street said:

Wow, that is an work or art!  Good for you, I'm not sure I'm that motivated but its good to know you can make a smoker on the cheap.

Thanks! If I were you I would take it to a shop then - no point in guessing what parts to replace and wasting time and money on changing perfectly good parts.

 

The problem is finding a shop that is competent/good at diagnosis and will not also waste even more of your time and money changing perfectly good parts.

[428street]

My plan is to take another look tomorrow with a fresh set of eyes and patience.  Right now there is no CEL but I'm sure it's coming.  Drove it today for about 15/20 miles and on the highway driving spiritedly 🙂  It's worth another investigation of the sleeves and clamps at a minimum.  Plan is to loosen up and see if I can rotate them (sleeves) and inspect for any cracks, etc.  I know I tightened them pretty good so gonna try and get them snug as opposed to tight.  The sleeves and seal gasket for the TB are relatively cheap so not super worried.  Also going to stop by the local Indy in town and see what kind of place they have as well.  As much as I would like to do it all myself sometimes it makes more sense to pay someone with a lot more experience than me.  Its a big difference to read about it and technically understand the problem than to have actual time working on these cars day in and day out.  Can't compare.  This is not a daily driver so I have some flexibility from the standpoint I don't need to rely on it every day.