Gtbfever

1981 US 928 16v…..Does anyone know if one of the bigger vacuum lines on passenger side of engine was supposed to have a restrictor or flame trap in it? (I thought someone was playing tricks and found some plastic in the line like a plug-so I removed it) I cant remember which line….would this cause idle surging and car bucking to the point where I have to push in clutch to stop it from bucking and keep it going…..I’ve replaced…fuel pump,fuel filter,fuel dampers,fuel injectors new flow tested oem,all seals new,all new fuel lines (steel & rubber)..new temp 2(Porsche oem),and all other water bridge sensors,new cap,rotor,wires,Bosch copper plugs,all vacuum lines replaced & smoke tested,new coil,new ballasts,new egr valve,new diverter valve,new o2 sensor,micro switches click-for full throttle and idle,new throttle cable,afm opened and checked and re-sealed,new big sealing oring to afm,new seal to airbox,aux air valve tested good,new electric air valve,vacuum limiter tested held vacuum,thermo valve tested,heads rebuilt,bottom engine all re-sealed,new water pump,timing belt,new porken tensioner. Only thing I haven’t done is check connection to l-jet brain and check for corrosion and or a bad brain? What else am I missing??

The Forgotten On

A common issue for surging is putting the wires for the throttle sensors on the wrong microswitch. It causes the ECU to think it is WOT at idle and vice versa.

Andrew Schauer

Yes, that restrictor is a stock piece. It's part of the vacuum generating venturi system for the brake booster. But I don't believe it would affect idle, only larger throttle openings.

The idle microswitch isn't required to run correctly, you can help troubleshoot by unplugging it.

Mrmerlin

post some pictures of what your working with please

Gtbfever

New brake booster…..green wire looks great shape. 14pin appears un-corroded….but like I’ve said….haven’t checked plug connections to brain. And I might try swapping connections to micro-switches!

Mrmerlin

I was looking for a picture of the line where you found the restrictor,
need more detail,
NOTE someone else was suggesting the venturi Eductor was an issue,
.but thats on the left side of the engine.

Gtbfever

Yeah….about that. I threw piece of plastic out…it looked like the top of a GM touch-up bottle cap(if you know what I mean?) and I also don’t remember which line I found it in. That’s why I was wondering if anyone ever ran into this?? It was about in this area circled in red. I was wondering if it was in a line going to fuel evaporation??