Bad AFM ?
 

Been having a lean misfire once warmed up lately, does fine when cold... closed loop. Was advised to change AFM, figure after 30 years and 800k plus miles couldn't hurt, right ? Got the remanned unit today put it in, start it up and its missing belching black smoke ,,,,, WTF ? Even thru the CEL ! Swap the original back on, no smoke, CEL goes out on its own ! What am I missing. have another AFM coming in Thursday .

Advised to change the AFM ... why?

What are the symptoms of your miss... at idle, certain rpms coasting down hill and barely touching thre accelerator?
what engine 22re or 3vze

I don't think they change the circuit board on remanned ones. I just ordered one since I had some dead spots on the restrictive strip on my orig one. Remanned one had more dead spots than mine so it is going back. Here is how you test you AFM: http://htftp.offroadsz.com/marinhake...33volumeai.pdf

When was the last time you adjusted your valves?

Put second replacement on, runs better then it was. this one however has some kind of adjustment on it. original and first one did not, any ideas ?

sig says 22re

Idle control air valve would be my guess.

Seems like it is slightly getting worse.... IAC was changed out a while back due to not returning to low idle, could it cause the erratic misfire at idle somehow ?

I would take it out and soak it in carb fluid and re-spec the tps.

Open loop is when the engine is cold and closed loop is when the engine is warm. Unplug the O2 sensor and see if it still has the same symptoms. Unplugging the O2 will force it into open loop and will determine if the problem is related to corrected fuel trims.

Oxygen sensors do wear out, so that is a good place to look.

Lets go back to the Air Flow Meter for a moment. I am unsure how much the AFM plays a role in the problem you are experiencing (there are many potential causes), but it would be good to know if the Air Flow Meter is working properly.

Do you have a multimeter and know how to use it?

If so, the Air Flow Meter can be electrically tested to make sure it works as it should.

Here is a good write up on testing the Air Flow Meter using the Factory procedure: http://www.4crawler.com/4x4/CheapTricks/AFM/index.shtml

:safari:

Check your intake tube between the AFM and throttle body for cracks or tears. Leaks can cause missing and rough running. It is a quick and easy check. Then test the AFM as old87yoda has recommended.

Unplugged it and still acts the same... with the addition of the CEL of course. So, this tells me what now.... o2 sensor is good, correct ?

Yep.

Check the iacv and both coolant sensors and make sure they are functioning properly. If you're having a cold loop hot loop problem that's where I would start.

All the IACV does on these is speed up the idle when cold, correct? What is the proper method for testing these. Packed up repair manual in storage till I get moved , TIA

Something like that. But if stays stuck in the open position it messes with idle. Take it off and put in boiling water and verify mechanism is opening and closing. Also check the green coolant sensor. It tells the cpu info for the loops.