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Message: <blockquote data-quote="poisonbl" data-source="post: 1138095" data-attributes="member: 17541">Well, as a few have probably heard me mutter about this over the past month or so on chat... I have a semi-inconsistent misfire issue. My guesses so far:1) My hope, really, was bad/wet gas - ruled that out with a couple tanks between then and now and some water remover.2) Fuel pressure (pump, leaky injector, or regulator) - tested pressure at the rail, it's steady, holds solid at 40psi when I kick the key to on and leave it, and is well within spec even while it's misfiring and trying to kill over. Part of the root of this guess is a potential electrical issue to the pump, where my tail lights/blinkers/brake lights going on or off cause an audible change in the tone of my fuel pump, but the change in voltage (at the inertial cutoff switch, it was the lazy way to test) is at most 1 volt.3) Distributor cap dirt/residue - Cleaned this up for a tremendous change in appearances (aka there was metal visible again) but there was no change in how poorly it runs. No sign of any excess scarring or such in the cap, though the rotor's slightly pitted along its edge. Now, the way it's acting. Starting out at a reasonably cool temperature, 90% of the time or so, it runs perfectly fine, to the point that it performs great, jumps off the line at lights, goes WOT without any hesitation, and it runs fine until I end up idling for around 30 seconds or so at a red light/stop sign. At extremely cold temperatures, the one morning I have to work from, it started out rough from the moment I turned it over. Warm days, it's been about 50/50. Starting out with the engine already warmed up, the issue's immediate.When it's running rough, RPMs drop erratically with a dull 'thump' more than a 'crack' from the exhaust/backfire. If it's in gear with my foot on the accelerator  it feels like I just reached the end of a chain attached to the rear of the car, the whole car lurches, and continuing with that seems to make it worse (though that may be an illusion caused by my foot bouncing on the pedal), and heading up a hill just makes it worse. Even when it's rough, it'll have stretches where it acts fine, usually around 2k RPM, but 1-1.5 has also smoothed out more than once. When it's actively missing, reaching 3k is nearly impossible, as it just bounces between 2k and 2.5ish when I've tried, hitting some invisible wall. Sometimes, pushing it past the 2k mark at all seems to kick it past whatever the immediate issue is and make it level out again. The problem exists as much at idle as it does with and without load moving down the road. There's no noticeable knock or tick, even when it's misfiring, and, actually, at the engine itself, the misfires give... a disturbing instance of just plain... silence. It's died on me a couple times, but only when it missed just after/as I came to a stop. It's come close to dying on me a couple times, but those times it dropped RPM drastically, then seemed to just... start itself back up, refusing to give in.So... given all of that, I tested vacuum today (just got a gauge in from ebay). It's a good, clean, 20 in-hg for a second or so from startup, then it drops to bounce between 15-17, generally in rhythm with the miss. Suspecting a valve issue, ran some seafoam (not nearly the thickness of smoke out of the exhaust I expected, but still impressive), and... had smoke from somewhere seemingly low on the driver's side of the block (poor lighting, after dark in a large, empty, parking lot... since rolling that amount of smoke at my apartment would make my landlords very unhappy people). I don't smell exhaust when I'm under the hood with it running, or inside the car (unless I sit and idle for a long while with windows and/or the top down), so I doubt it's at the exhaust header.Now that I have more than just an obscure could-be-anything miss... I'm strongly leaning towards a blown head gasket, if not a warped head. Before I dive into tearing that apart, anyone have any tips on what to look into as other likely/vague possibilities?</blockquote>