Here are the pictures (left hand index finger points at Diag. port location):

http://forums.pelicanparts.com/uploa...1719455695.png

that was an interesting video and very helpful. My ford van has a similar thing like that, its called a "spud connector" , overrides the computer control so you can set up the timing. my reference was to a similar thing with my 89 volvo 740 shaking at idle, running fine otherwise. which is off topic here, but the symptoms are very similar. it has an AMM like a bit newer Porsches than mine , mine is early 85 so it uses the barn door. but the concept and design are very similar on my porsche , its just a little older. similar problems with the air intake leaks, they really do mess things up. ill pay attention to this when I get to this stage on my 944. Its been patiently waiting while I get my dayly drivers all lined up and working so I can focus on my toy. I have some holidays coming so Im hopping to dive in and do all the things a car that was parked and neglected for a dozen years needs. not sure where Ill start in but though maybe the brakes, then the timing belt, clean fuel system, tanl is dirty, new screen fuel pump, filter, etc. replace a bunch of hoses flush rad etc.. cap rotor plugs wires, usual stuff that fails, then I can try to start it.
Il make sure I do whats in the very helpful video once I'm doing the tune up sequence, and also refer to the garage site and the manual.

Ive been itching to go and murphys law, other stuff that is important keeps breaking around the house..dragging me off my fun project.

In the meantime reading here has helped a huge amount so I don't really regret the delay, the learning before I delve in will help me make better decisions, it'll be a rather lengthy process.

MW,
since you tinker with Volvos, you can work on Porsches with, I might say, some sort of pleasure.

I always loved Volvo 240's , owned lots of them and drove millions of miles, you can fix almost everything with a standard toolbag.
the 740's I have are almost exactly the same so far as the engines and controls. The technology is a lot similar , and as we went through the 80's both had advancements at around the same dates. a DME in a porsche and a volvo ICU are proprietary designs, so are the engines, they are both all bosche electrics, even my 88 ford 6 cylinder 300 van is, as well. some differences in terminology.. such as the letters representing an idle air control valve, my van has one too, looks different, but similar in function.
some of these parts arent; porche parts, they are bought from companies like bosche who may also provide the same part for other vehicles. a lot of the parts are proprietary.

after watching that video, that mught help the OP, he was having trouble wiht it idling and someone has evidently screwed with the throttle stop or similar so it wasn;t making the switch, probably because they didn't do what was in the video , disable the ECU from interference while setting up the timing and idle, enguage it again, see if it goes astray, if so disable make some corrections , so when the ECU ( or DME) takes over control its not making radical adjustments to override stuff, in order keep the engine running. as I see it he's basically getting thhe car to run in somewhat a state of equilibrium so that the DME is making adjustments from that point.

in volvos they employ knock sensor , I thin k my ford van does as well... if the engine starts shaking like its about to stall the ECU adusts the timing to try to prevent a stall. Ill notice it happen particularly if its not running well due to vacuum leaks etc.

I'm not sure if the Porsche employs a knock sensor. you wouldn't want the electronics to be overriding the ignition timing while you are trying to adjust the timing. doing so may cause the back yard mechanic to set his timing incorrectly , similar with the idle adjustments.

if it's not making the throttle closed switch then the computer doesn't know the throttle is closed so trying to get it running well in that state without correcting the problem of it not making the switch is basically leading into further maladjustment of other things. Next you can have the timing and any air bypass adjustments or the throttle plate stop and things like that compiling. going back to the factory tuneup info or maybe the Clark's garage instructions (which take into account the Porsche shop manual instructions) is the answer.

turning too many screws without following the proper procedure can confuse a guy down a bit of a slippery slope, next thing three things are a little out of adjustment and the sum is still not a properly adjusted system. a proper porsche mechanic will probably tend to follow the factory suggested sequence and instructions.. so he is less likely to get caught in that multiple poor adjustments scenario..

giving the throttle body a good cleaning first might help things. the throttle shaft rotates and if that bushing gets loose, it might suck air in there through a now loose fitting bushing. I'm not sure if it's every common but a bit of play can perhaps create a little air gap around the throttle shaft. stuff like that may be minor but also may stack into other tune up problems,

the reason for adjustments and not fixed settings is often to account for such wear in parts over time.

as an example, maybe some minor amount of air does bypass because of wear in the throttle shaft so the mechanic completes the tuneup sequence and maybe he adjusts an air bypass or similar to compensate. this affects the idle speed.
the wear was predictable, It may not actually need a new bushing to run fine, it needs an adjustment to compensate.. a total rebuild may involve new bushings, new throttle shaft, and that bushing is just an example..