97 blows black smoke

4.0. Only code was for MAP high voltage. Checked, reading normally at that time. Belches black smoke, but oddly runs well under all throttle settings but idle. At idle it runs exactly the same as a typical vacuum-unplugged MAP, but removing it from vacuum makes it run no worse.

Check your spark plugs to see if something wierd (bad) has happenned in one cylinder.

my 87 was doing almost exactly that. it would come out of it for a few seconds every now and then though. It ended up being my ecu

Not the ECU, not isolated to one cylinder.

Black smoke = rich mixture.

Exhaust gas analysis/engine analyzer or a compression check on all cylinders would be a good starting place.

You guys are swinging and missing here.. black smoke = rich, yes, what do I do now?

If the mixture is fine everywhere but idle then your first culprits are the IAC, TPS, or ECU, and associated wiring.

Update. Replaced MAP, reset codes. Still running blubbery rich at all rpm's, very rough idle. Codes now P0300 and P0174, misfire and lean code.

Engine thinks it's running lean (too much oxygen in the exhaust), it's actually running way rich (too little oxygen in the exhaust.) Have you checked your O2 sensors and associated wiring? Perhaps that relay for the O2 sensor heater(s)? At work so I don't have a schematic in front of me, not sure the 97+ still had that relay.

X2 on the O2 sensor. Make sure the computer gets to see what it needs, then sart tracking down what may be a vacuum leak. Possibly re-torque the manifold bolts, maybe a new gasket. Get the big, cheap stuff out of the way.

Bingo, long and short fuel trims pegged. Upstream 02 voltage a big fat zero volts. Why it didn't throw a code for 02s not switching I have no idea, different pcm's seem to have different intelligence levels when it comes to monitoring capabilities, obd2 or not. Replaced o2, runs like a champ.

Not getting a code from a faulty 02 sensor is a common issue across all brands of cars.

I think that one that is operating properly starts to 'wear out', and fails gracefully, thereby not alerting the ECU to it's sudden demise. Our two '96s are over 140k and 150k, and niether has thrown a code, but with an item that's made to last <100k, surely they've gone by now. On my '96, I replaced it in the 120s, and the MPG jumped right up. My '92 had the 'Maint. Reqd' light, which goes on in the 80s. Replaced O2 at about 130k, MPG highway went from 15~16 to over 23. Paid for itself quickly.
We had a '98 ZJ, O2 went at about 65k, threw a code. Replaced it, and id did better, but light kept coming back every few weeks. Got to where we kept the scanner in the car, and whenever the light came on, cure it in about three minutes. Dealer said the computer needed to be re-flashed, to recognize the new piece, but wanted over $100 to 'diagnose' it. I reminded them that emissions were warranted for 8 years/80k miles, and I was told they may refund it. They lost a customer for life.