"Trailer-hitching" bucking problem, Rapid detrioration from running perfectly Options

[boxster914]

Hi everyone

My perfectly running 71 914 1.7 D-jet has deteriorated rapidly this past week.

Early in the week I noticed what felt like a power drop out during a drive. It was very slight and only happened once and I wasn't sure I didn't cause it by unconciously lifting off the gas.

The next drive it happened a few times and was more pronounced. It was then that I knew this wasn't an imagined problem.

On the third drive it was like a bucking bronco, surging and stopping and the engine cut out a few times. It was undriveable.

Today it will start but won't run. The engine cuts out when I try to rev it and the red light comes on.

I've done some searching here but haven't been able to draw any conclusions or come up with an actionable strategy to diagnose the problem. I'm seeing people trace it to spark plug wires, air fuel ratios and bad distributors.

Is there a step-by-step process that you can recommend for me to get to the cause of this? (I'm a newb so I probably will need help with abbreviations like AFR, TPS, etc.)

Here is a video of it's rough idle yesterday when it was still running.

https://youtu.be/n61CP6O8UgM

[wonkipop]

if its anything like a L jet, its the vac retard line from the distributor to the throttle body.
not sure exactly how they work with D Jet but know in L jet its to retard the ignition at idle mostly. it retards timing when there is engine vac, in L jet its on the manifold plenum side of the throttle body so its functioning when the throttle plate is closed at idle. mostly there to assist with emissions on L jet.

D jet guys would be able to tell you exactly how it works on your car.

but aside from it possibly affecting the retard which i don't think is significant in terms of sitting there idling it would have been an air leak into the system.

combine that with your fuel pressure or fuel restriction problem and your mixture leaned right out. why it wouldn't idle, hard to start and was bucking.

you have probably been driving around the minor air leak (and it does look minor) for a while and not even noticing it. i think your main problem might have been fuel restriction. the air leak would have exaggerated it, perhaps not a lot.

good work solving it.

(IMG:style_emoticons/default/beerchug.gif)

EDIT
ps
when i think about things back two years ago the problem i had was very similar.
even though i have L jet.
a combo of fuel and air leak.
i found the air leak first. it was the throttle body gasket had done hard.
as soon as the engine really warmed up thermal expansion difference between the throttle body and the plenum caused the leak. it wasn't much of a leak i thought but it was around probably 1./2 the perimeter of the throttle body. new throttle body gasket and the problem seemed to go away. a bit like yours subsided after the filter change. ....that was until i ran the gas down to a 1/4 of a tank.
see my posts earlier in this thread. i am glad your fuel problem was a little easier to solve. my own fault for "butchering" the car to convert it to rhd 30 years ago. (IMG:style_emoticons/default/smile.gif)