Misfire after ~3500 rpm, persists for about 60 sec

Hi all!

Want to start off by saying that I'm new here, thanks for letting me join!

Alright, I have an 88 TC, with no mods. When moving, as soon as I hit 3500-4000 RPM whether or not I'm at WOT, it feels like I have a misfire. I don't know if it would be valve springs as it persists for about 60 seconds thereafter. It will misfire whether I'm idling, or still moving, and again, no matter what I'm doing the misfire will go away after 60 seconds. Another issue is that as I'm pulling into a stop, I put the clutch in and take it out of gear. The RPMs will drop near stall for about a half second then recover to normal idle speed.

Here's what I've checked so far:
VAM is good
TPS is set correctly, doesn't jump in it's sweep
IAC is good
EGR disconnected (still occurs when connected, doesn't matter)
Fresh plugs, wires, plugs gapped to 32 as per sticker in engine bay.
TFI has been replaced with a known good TFI, didn't help.
The chingadera inside the distributor has been replaced, didn't help.
Timing set at 10 degrees BTDC with sp-out disconnected
No vacuum/boost leaks that I'm aware of.
Compression is 140 all cylinders
Stock FPR replaced with new stock part and adjustable FPR, both no change.
Fuel Pressure stable and at correct level, rises/drops with boost
Fuel is new, 91 octane
Fuel filter hasn't been touched by me, but assured by previous owner that it is new (less than 5k miles on it)
Assuming fuel pump is good because I don't have drops in fuel pressure under load

Starts and idles real nice, no misfires there, drives like a dream around town, but as soon as I'm at 3500 rpm it starts misfiring. Oddly enough, it does not misfire if I'm sitting in neutral revving to 3500, it only misfires if I go to 5000 in neutral.
2 things my father suggested I test :
Set the timing to 15, go WOT: experienced major pinging but NO misfire - NONE.
Disconnect vacuum to FPR, WOT again: Lean as all hell but NO misfire - NONE.

I am stumped. Engine runs perfectly normal, temp gauge needle is right in the middle when running about town. What do I check next?
Please help!

PS: FORGOT TO ADD - WHEN IT MISFIRES IT ALSO BACKFIRES WHEN THROTTLE IS "GOOSED"

Have you checked your cam timing? I've had similar issues with other cars due to cam timing.

What TFI do you have?

If its not a motorcraft, it could still be the issue

The parts store brands, wells and bwd, along with the really cheap ones dont seem to ever work as well

Sounds like injectors to me. Pull the vacuum line of your regulator, if fuel comes out while the engine is running, then it is shot.

^^^^ Even if the FPR vacuum line has a somewhat strong fuel smell to it the FPR is shot.

My first thought was valve springs, but that doesnt make sense since the engine free revs fine. Have you pulled the plugs to read them?

The chingadera inside the distributor has been replaced, didn't help.

What *I* want to know is, is the "chingadera" a Motorcraft part, or can I get one anywhere? Sounds cool, I think I need one, I just have a regular rotor in mine. :giggle: :confused: :rotfl:

Seriously though...I'd agree, sounds like a fuel issue. Why not "tee" in a fuel pressure gauge and see what pressure you're getting at 5000 rpms at idle, up down or the same?

Have you pulled any EEC-IV codes?