I was reading through this from the beginning. Correct me if this is wrong.

Car idles badly. Will drop low when coming to a stop, sometimes dies
Dealer said no codes found but suggest maf, injectors, coils
Another shop said it is misfiring

How did the 2nd shop see it was misfiring?

After I changed out the coils I scanned the car with my (Durametric) software .I selected all the cylinders and cylinder 4 started counting ,so I figured out cylinder 4 is misfiring .When the car was at the Porsche dealer they said my car is not throwing any codes so they recommended trying to replace to mass air flow sensor 904 dollars . After that they said my car is showing multiple miss fires on several cylinders .I need to replace all my coils because they were aftermarket .Replace my injectors and plugs .To get the car running right. This did not make sense so I picked up the car .They had it 4 weeks and never mentioned any codes till after I ok-ed the mass air flow . And now they want 2200 more . I don't trust them .I have had my car to 5 different indi around the the spring Texas area no one lives to to the expectation .I guess I could disconnect the front mount and let the front of the motor hang down a bit ? It might give me enough room to remove the injectors ? I don't know. I spend way more time working on this car than driving it. I can understand why one would want to push his car off a cliff . I have had to replace the steering rack twice the axle brake master cylinder clutch , clutch slave brake rotors twice . The suspension has been changed to coil overs .All coffin arms a Motor head lights changed to Litronics a horn radiator fans ignition switch steering lock The seats have been redone new sifter new starter new glass window top new radio .wheel bearing .So much stuff I sure I missed something .I have to much money in her to give up now.Oh yea had to replace the heads on a 3 year old RND engine .That now need to be replaced again . Thank you all

I dont think your motor needs to be rebuilt/replaced.

Now, I do think your car is cursed. lol

I think this is what Blue is suggesting to use to check the misfire. Unfortunately, #4 is the biggest pain to get into. https://www.amazon.com/Tool-Aid-36350-Line-Checker/dp/B000VULAQC

I have something similar but without the injector testers.

I'm in the same boat as you. 4 places and 4 different answers/suggestions/costs including the dealer. If mine continues I am having it shipped to KC rennsport for him to take care of but so far I am doing better (at the moment anyway)

Yes...Not as elaborate as that but for the money the one you provided the link to would be nice to have.

When you use something like that your testing the wiring to the coilpak and the coilpak and I believe the sparkplug all at once. Your not testing to ohm spec. but you know if your getting spark or not.

No need to undo wiring to the coils and move them around. just to see if a coil is faulty. Then you still have to test wiring and plug separate. switching coils side to side wastes time and is a incomplete test and a poor diagnostic procedure.

So I'm an idiot. I read the vacuum gauge wrong .Its reading 20cm of vacuum not inches , indicating late valve timing so I have re-check my cam timing ?

The scale you want to read is on the inside of the dial.
Your showing very low vacuum in the video. Looks like lees then 7 in.hg
Where is the gauge hooked into the intake at?
Also you want to use as short a hose as possible from gauge to connection to the intake.

There is a rubber tube connecting rear flapper to left and right phelumn .Each one of these rubber tubes has a vacuum line .In my car one line goes to the fuel pressure regulator .I tee into this line between the regulator and rear connecting tube. The line is six feet long or so.

you dont want to be connected there. It's better to connect right by the 4 way where the check valve is on the plenum, near the AOS

If I am picturing it right in my head then that should be ok.
You can double check by hooking to another spot and see if you get the same readings.
Also try a shorter hose to the gauge to see if that changes readings. Sometimes to long of a hose lowers readings.

I usually tee into the intake at the SAI connection to the intake. There is a little one way valve there that is easy to get to and remove so I can insert the tee fitting.

The hose going to the flapper though is controlled by the change over valve.

T into the yellow ones, they are easy. The red is where you dont want to T into, that will be DME controlled with the change over valve.I think Blue & are talking the same thing with the check valve.

http://986forum.com/forums/uploads02...1627950020.jpg

I see now (pictures help)
Yes connecting to one of the hoses you have marked in yellow is best.
Red hose with change over valve not good. Probably going to get incorrect readings.

I was watching the gauge in his video and the RPM the needle just was not acting they way I was expecting in relation to the RPM.
That is why I asked where it was connected.
So he needs to connect to another spot and run his vacuum test again.
I usually tee in ahead that one way valve in the bottom of your picture.
The small black and white one.

I just reread the post and it seems that he is teeing in at the hose marked in yellow on the upper left side of the picture. So he is ok there.

I think so too but pictures always help

Hi Stl and thank you all for this post. I’m having the same issue and I have a Durametric that’s just arrived - could you point me in the direction of what to look for or test?

Look for what?

Would be better to start your own thread if you are having issues.

Yes I am connected to the line going to fuel regulator . After my heads cracked I put the motor together by one of the articles on how to install cams .It is done with the tensioners out .They get put in in later steps .I checked timing marks and every looked ok .I just read an article where I guess I should of done it differently so I am going to attempt to set the timing with the motor in the car.Any suggestion how to do it successfully ? Thank you guys.

when you did that, it is the correct process, but just checking & adjusting timing you dont need to remove them if all you are doing is adjusting timing.

I removed the injector from cylinder 4 and checked it against a new factory injector and it ohm's out the same, connected it to a battery momentarily and I can feel it opening and closing . Next I will check timing but its looking like a valve problem.

Miss-fire gone .I went to reconnect injector and said to myself check the colors of the wire going to the injectors and low an behold I had connector 4 and 5 on the wrong injector .Durametric showing no misfires .Roughness indicator is flat lined ...So it looks like I'm to blame for this problem .What I don't understand is why was the software only showing one cylinder misfiring? So I'm going to put the car back together and se if it dis when coming to a stop. So The scenario is accelerate rapidly stop rapidly idle drops below normal and car dies ?

Interesting. How could you have done that though? The wires are pretty much set to the length, unless they were really stretched

Some OBDII systems will shut fuel injectors off under certain misfire conditions.
The feature is designed to protect the Catalytic converter.
So then they do not show misfires for that cyl.
I do not know if Porsche of the early era's like ours does this or not.
Doubtful but possible.
Info on the more advanced workings of the Porsche ECU's is very limited

Crossed injector wires would explain the backfire through the intake.
I bet if you do a "PROPER" LOL vacuum test now your numbers will be improved.

The wire harness was not stretched the wires going to 4 were the longer ones or so I thought . So 2 points to who ever asked if the wiring was right . I am happy to inform everyone the backfiring is gone . I assume it was firing fuel as the exhaust was opening . I don't know . Motor is running much better punching the accelerator from an idle car rapidly accelerates with no bogging or pooping seems like it's running right . Tomorrow I will button it up and go for a test ride.Thank you to everyone for all the help and guidance .Thank you all. Thank you.

Good to hear you got it sorted out.
The backfire into the intake was happening because it was firing with the intake valve open or partially open.
I tried to list all the ways that can it happen in post #24.
missed fuel timing:eek:
As happens most times it was something so simple it was overlooked.;)
Let us know how the test drive goes if you have time.:D

Test drive went great car revs out .Got on the free way opened her up got the motor up to operating temp pulled off came to a stop and the rpm's are not dipping below normal and the best part the cars not stalling out when I stop ..Yea .It is amazing how something so simple can cause you to pull your hair out .Thank you all . I called the Dealer . I should not mention their name but they refuse to refund any money .PORSCHE OF NORTH HOUSTON .Are not very good mechanics . I told them That I took the motor out I put it back .They said they needed 3 hrs. To go over all the obvious stuff . Only 140 an hour because its a classic . Recommends replacing the mass air flow after I told them I tried both that I have and it made no difference Total for the bill was 904.00 I did ask to have the clutch slave bleed while it was there 120.00 I am not very happy with the dealer .All their expertise tools, software and they could not figure it out . They should be extremely embarrassed at the low level of customer service and on top of that wanted 2200.00 more to fix it .The first time I had my car at Porsche of North Houston they ripped my top and tried to say it was like that .I should of known to never go back to shop but I took a chance because I was desperate . I am a toolmaker /Designer not an auto mechanic . I know way too much about this 986 .L.O.L. Thank you all for pointing me on a path to success . Thank you all. What did you do with your Boxster today fixed it again .

You could do a report to the Better Business Bureau.
At least that would be on record.
In the end its running right.
Have fun with it.
Touch base now and then here on the forum:D