Hey all! I have recently begun diving into an 88 740T. As I get deeper in this project, it's starting to resemble a can of worms, literally; wires loose throughout, hoses inaccurately linking, moist undercarriage. The problem I am specifically trying to remedy with this thread is stated in the title.

I took apart the entire hot-side and intake to intercooler last night to replace EM gaskets, check on an oil leak at the turbo oil return, and scratch my head about oil in the intake - return leak solved, oil in the intake NOT from the turbo itself :hew::.

One of the instigating factors for doing this was very weak power from 0-20. On any incline starting from stop, the struggle is real. WHAT GIVES!

In my can't-sleep-staring-at-the-ceiling-must-wrench thought process here is what I surmise: weak spark, bad O2 sensor, weak injection, weak fuel pressure, unmetered air entering system.

Through various inspection, here's what I've noticed/fixed: O2 sensor coated in white residue, Turbine coated in same residue, contact points in Dist Cap and on rotor blade gunked with electrical burn-off so I scraped that off as a quick fix, unmetered air entering system because I have gorilla hands and broke the black little twisty valve below the throttle body (idle intake valve?).

Now IIRC, the white residue is symptomatic of two possible items: lean burn, and/or coolant leak in head gasket. The former can be dropped because this thing guzzles 93O like a top-fuel dragster and the exhaust smells so rich.

Which brings me to my hypothesis:

fuel injectors are spraying well for the amount of metered air entering the system, however, a weak spark is not combusting all fuel vapor creating a lean exhaust that smells rich and is not registered by a busted O2 sensor. So I should change the spark plugs.

Questions Being:
Should my order of operations be: Plugs, wires, O2 sensor, fuel filter, Dist Cap?
Does the RSR or Fuel Pump Relay play into this at all?
RSR on my vehicle should be drivers side?
Does the ignition module play into this at all?
I snapped that twisty valve, half in my hand, the other half still in its home, checked last night to see if I could reach it, nothing was there, checked from by the throttle body, nothing was there, what happens if i can't find it?? any chance it got jettisoned out onto the road?
Is there anything else I am missing? Or that you need to know to help?

 

sure, those basic tune up items should be addressed!
O2 sensor, not yet, fuel filter, no.
Relays, no.
Ignition module, no.
Not sure about the valve you broke, what it is?
You may have an unmetered air leak, sucking too much air=too much fuel.
You may have a bad main fuel pump.

 

looking at the intake manifold, the valve/**** is at 6:45 in reference to the throttle body

 

If that's the Idle Control Valve, you need to get it replaced before anything else! There's a couple of 940s in the Portland Foster PickNpull, may be have the valve there.