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'93 940 turbo stumbling and dying

Hoping that you're nearing the end of the trials here...at least on the engine. Not sure where you are in Maryland, but I can lend a hand on a weekend if you need to drop the tranny.
Thanks MDDave! If these trials continue I may take you up on that offer.

Haven't measured the plug wires yet, but they're fairly new ngk wires. I'll break out the multimeter to be sure.

A confession: my "stock maf" was borrowed from the girlfriend's daily 940 turbo as I couldn't find mine. Grabbed another 016 maf from a friend and had very different results. No more clutch slipping, but now the car will start and immediately stumble and die. Giving it some gas gets it idling but a little low, 4-500rpm. Disconnecting the maf makes the car stall out so I assume that's working. Disconnecting the iac doesn't change anything, pulled it and cleaned with pb blaster but the results were the same. Pulled the throttle body and put in a fresh gasket, cleaned the butterfly valve and reset the idle screw and tps for good measure - alas, no change. Pulled the spark plugs and they were dark and smelled like gas, but the wideband in the car reads 14.6/14.7. Driveability is terrible. The car is stumbling in all gears, not just during acceleration. Tach reading doesn't change when it stumbles. Reset the ECU and nothing changed.

I'm going to try cleaning the spark plugs tomorrow, might throw in a fresh set of plugs too or see if I can grab a spare iac to rule that out. But I'm running out of ideas.
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Know this doesn't make a ton of sense given your AFRs, but this sounds like a fuel issue.

Where did you end up with measuring fuel pressure? This sounds a lot like my car when the main fuel pump up and died. At least the idle behavior, it wouldnt run long enough to drive.
Mini update: I've discovered that my wideband has likely been reading incorrectly this entire time. A new one was fitted last night and the car now reads high 10s to low 11s at idle. When I get a chance to drive it I'll see what the gauge says at different throttle inputs and boost levels.

To those shopping for a wideband, avoid my pain and wasted time and make sure your wideband comes with a Bosch sensor in the box, not a cheap knockoff.
Forgot to answer MDDave, my fuel pressure while driving around checked out.

Some numbers from my drive to work this morning:

Idle: 11.8-12.4
Light/Moderate throttle: 13.6-14.4
Heavy/Full throttle: 10.3-10.8

I also noticed that if i took my foot off the throttle completely while the car was in gear, the gauge would display three dashes. Going to do some more reading to see if it doesn't show off-throttle readings under load or if this meant I was leaning out. Idle and acceleration all around were terrible and shaky, heard some popping through the intake under heavier acceleration a few times. Going to try stuffing the guts of a spare maf into the housing of my 3" one and see if that gets my afrs a little less rich.
Three month bump because I'm back on my bull**** again.

Turns out the clutch was slipping - to anyone else planning a t5 swap, ensure your trans is fully flush with the adapter plate on the bellhousing. I put the bellhousing+plate in the car first and then attached the trans because it made it easier to lift without a trans jack, and mine was off enough to cause uneven engagement of the pressure plate. Fixed and the car is now slipless.

We're back to bucking hard if you floor it again. The girlfriend followed me on a test pull and said that when the bucking occurred I shot flames out the tailpipe. While very cool, I'd prefer speed instead. Since my last post, I've switched to NGK bpr8es plugs gapped to 0.025". bougicord plug wires, inspected and cleaned the distributor, running a reman'd 012 maf, new redblockpowered chips (thanks cam, my afr's are finally healthy). IAC and ignition amp have been replaced, tried advancing and retarding the cam gear, tried bpr6es plugs instead, all with no change. I'll try to grab a video of the bucking if I get the chance, but anything else I should check?
Checked mechanical timing and it was dead on, bucking issue persisted. Swapped in a known good CPS and no change. I've had all the bits for wasted spark sitting in a box under the coffee table for a few weeks now, so I went ahead and tossed all the stuff in. Fires up and idles great, but from parking on the slight incline in my driveway it seems a good amount of fluid leaked out the breather hole on my t5 slip yoke. Because I insist on trying the thing I know I'll regret before fixing it properly, that hole is getting some JB weld. I'll drain and refill the trans soon and get the car on the road for testing.
JB weld seems to be holding, trans once again has fluid and a test drive was taken. Bucking persisted, afr numbers were all over the place at cruise and it felt like the car was having an intermittent miss while cruising around. Tinkered with it over the course of the weekend while growing increasingly frustrated before I finally decided to check my wastegate actuator.

Imagine my surprise when the arm of the actuator was completely gone. So the actuator hasn't been actuating for some time. I feel like quite the fool.

I've ordered a new one and we'll see if this solves the issues I've been having. I'm amazed - I expected to pull it out and discover a leaky gasket, not half the thing to be missing. Anyone had something like this happen before and know how to stop it from happening again?
Back again. New wastegate actuator is on and working correctly. Bucking is gone, but I'm having a strange issue im going to call "breaking up". Under light throttle, the car feels like its missing a bit. This happens in any gear and while working the throttle under the hood in neutral. The feel is like a mini buck or a shudder, a momentary loss of power. I've swapped between NGK bpr8es and bpr6es spark plugs with no change. My wasted spark coil is a brand new bosch 2x2 so I don't think that's the cause either. I'm using the miata Jwhatever ignition module, with the switched 12v hooked up to the blue wire from the stock coil and the "tach" wire hooked up to the candy cane wire from the stock coil. The car starts and runs this way, but I get no reading from the tach. Hooking it up this way with the stock coil in place gets the tach working, but the stock coil then wants to arc to the blue wire while running.

AFRs are normal at all times, cruise hovers around 14.6 and the mix richens up an appropriate amount under boost. Adjusting timing via the cam gear doesn't seem to change anything. No vacuum leaks that I can find.

Should I look for different switched 12v and tach wire connections for my wasted spark? This feels sort of like the stumbling it has done before on the stock ignition system though, I'm not entirely convinced my connections there are related to this behavior. I feel like I'm running out of things to check.
Smoke AND pressure test the induction system.

Restore to stock and then add crap back on one at a time.
Pulled out the halloween decorations box this past weekend and grabbed the smoke machine. No leaks that I can find, equal parts reassuring and frustrating. The throttle body gasket and intake manifold gaskets are both brand new, maf is a bosch remanufactured unit bought from a forum member I trust and hasn't been in the car very long. Throttle position sensor is new, iac is new. Fuel pressure is good at idle and load. Injectors were cleaned before install and the car has only seen 93 octane since all this mess began. Plugs are new ngk bpr8es, the bpr6es I have don't seem to make any difference when I switch to them.

New discoveries: The stumble seems to happen the most at very light throttle. The engine shakes almost like it's missing when you barely crack the throttle under the hood in neutral. Also while under the hood, there's a brief hesitation when you blip the throttle under the hood. If you rev it up a bit like this and then snap the throttle shut, the car will sometimes almost stall out but catch itself, and other times hang on to revs for what feels like too long for a car revving in neutral. While driving around it feels almost like it's cutting out for split seconds when you barely touch the gas in any gear. Anything past light throttle though and its very smooth sailing, with the misses happening only occasionally.

The coolant temp gauge does move, but is reading very low even after driving around for a bit. That being said I don't have any check engine lights, codes, and my afr gauge reads normal. The only things I feel I have left to test are the plug wires and the crank position sensor. I'm going to try replacing those and see if that changes anything. Might do that temp sensor just for peace of mind too.
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Those are both things that can cause strange intermittent misses while driving. I would suggest also double checking the plug gap as well. Take a look at the plugs and see what they have as a mixture indication.
Sounds like fuel pressure reg has failed. Try with a know good one and report back. Classic symptoms in my experience.
Sounds like fuel pressure reg has failed. Try with a know good one and report back. Classic symptoms in my experience.

And we have a winner! Put on a new fpr (and some kingsbourne plug wires, which I can now highly recommend) and the car is now where I wanted it to be from the start. Seems to richen up a little bit too much with boost, but not enough to cause any issues. I'm gonna call this fixed for now. Thank you everyone for all your help!
Catching up on your thread, so glad to hear that you were able to get this one licked. You had just about replaced the whole car!