D-Jet part-load issue goes away when TPS disconnected Options

[fslick]

I have a D-Jet question ('73 1.7).

Symptom is poor running/stumbling when transitioning from idle to part-load. It happens when the engine is both cold and completely warm, but seems to be worse the warmer it is (i.e. full engine temp + hot summer day). Starts and idles just fine hot or cold.

Interesting thing is that it's pretty much not noticeable if you VERY SLOWLY go from idle to part-load either with your tippy toes on the gas pedal or just moving the throttle with your hand on the throttle body. Of course you can't drive that way, so if you go from idle to part load normally or quickly, the response is poor and it stumbles but will catch up after about a second (or less).

Getting to my question, I took it to a [reputable] shop and they were able to figure out that it runs ok (at least doesn't have this problem) with the TPS disconnected.

I am going to take the car back to the shop to have them finish the repair (when they are free) but the engineer in me wants to know why this is a 'fix,' (albeit not the complete FI system). Also does it mean that the TPS is actually the problem? Is this a symptom of it being maladjusted?

(All the other usual suspects were checked and seem to be ok (i.e., new vac lines, new fuel lines, good compression and fuel pressure, fuel pump relocated, valves adjusted, checked dizzy, points, swapped ECUs for testing, A/F mix adjusted, replaced MPS, CHT, etc etc).
EDIT: I forgot to mention that replacing the TPS (with a used/known good one) has already been done as well.

Thanks for reading.

[fslick]

Thanks for the succinct answer and resources, Rob. Much appreciated.

I've checked out the [amazing] pbanders site before and this symptom really nails it:
"Engine bogs from idle (poor idle to part-load transition)", with the causes being listed as timing/idle mixture. The shop undoubtedly has set both of these.

In your case, if unplugging the TPS helps, I would bet it's still the issue. Is it "bucking?" That's a classic symptom of TPS wear (or, in general, the engine going very lean on and off rapidly for some reason). Of course you may have more than one thing going on.

No bucking, but at the same time I haven't driven the car at a constant speed for very long with the TPS plugged in because the part-load transition problem makes it tough to try (I live in the city). I'm going to stay on this path and see how it goes (try a new switch and make sure it's calibrated).