"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

[Lockwodo]

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

I can relate! I'm working through a similar intermittent issue with my '74 2.0 D-Jet. The 914 Tech Notebook is your friend. You might find this reference useful, see section "Procedure for Renewing and Testing the Fuel Injection:

chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/viewer.html?pdfurl=https%3A%2F%2Fbowlsby.net%2F914%2FClassic%2FzTN_Man06.pdf&clen=44162&chunk=true

I've replaced the fuel filter and checked and set the fuel pressure and verified it's stable when the missing issue happens, replaced the ignition wiring, disty cap, plugs, rotor, replaced the board on the TPS, cleaned the PCV valve, verified that the Cold Start Valve isn't leaking. The idle has improved. Now replacing all the vacuum tubing and testing the various sensor components like the AAR, manifold pressure sensor, CHT sensor etc. I think it's most likely a fuel/air issue so the injectors will be next. I also plan to have the idle mix set by a shop with a good CO meter. After that, if the problem persists, I'll be suspicious of the disty. It's a process of elimination but on the other hand, the car is 48 years old and I've little documentation on what's been done before.

Looking forward to any ideas/pointers that others have!