eastcoast

So this is my first post at Yotatech, but I have been trolling for a couple months. So every once in a while, usually while sitting my engine light will come on and the truck will immediately run like crap (maybe 3 cylinders) after a while the cel will go away and the truck will be fine. It does not seem to matter if it is cold or warm out or if the truck is cold or has been driving for a few hours. As soon as the light comes on it runs bad. In the worst cases I have no power and have to pull over. At one point I decided to spray some seafoam through the intake and the problem went away for a couple months. When it started to come back I did it again and it got better but not as long. So now im at the point (14 months later) where cleaning the intake does not help and the light is comming on more and more. I have searched for the problem for a while but have not found a similar thread. At this point I am getting around 15mpg on the highway (truck is empty except for me) and I rarely drive over 54 in fifth(I used to get 18 combined and 280 to a tank with ~400pounds of stuff). My city mileage is way worse and it alwals feels like I have no power. If I baby it I can get ~240 miles to a tank. When sitting and running I can smell it burning rich, almost like pure gas sometimes, but only from the exhaust. Now every once in a while (very rare) all of a sudden it feels like all the power comes back but only for a few seconds. I am handy with a multimeter and have lots of tools.
The only code I get is 31 AFM.

91 22re 4wd 5spd 150k miles. I have been a member of mr2oc for 6 years and was sent here by one of their members, he told me this is an A class site and he was right. I will post a fix when this is all over!

bugs1961

Download the FSM here http://www.ncttora.com/fsm/index.html and go to the EG1 section. Click on mfisyste. Open troubles.pdf. Page EG1-132 has the troubleshooting for the VAFM.

Sounds like a new vafm may be in the future, but the troubleshooting will tell you.

abecedarian

The code doesn't always mean a problem with the VAFM but if everything else is in order, then that could be the culprit. If the ECU gets a signal from the VAFM that doesn't "jibe" with the signals from other sensors, for instance if the throttle is open a certain amount but the VAFM doesn show enough air (or too much air) travelling through it for that throttle position, it could trip the CEL, or if the VAFM signal changes too rapidly, the CEL could come on.

Now, you mentioned seafoaming the engine helped... makes me wonder how your valve adjustments are, valve adjustments can affect air flow so that's why I asked that, and how your O2 sensor is. The O2 sensor may be failing too but not a catastrophic failure: more of one where the air/fuel mix is showing okay but not really okay, and the ECU is assuming it's the VAFM failing.

By all means do check the VAFM according to the FSM mentioned above, but if it's okay, I've given you a little more to look at.

eastcoast

Thanks for the info I will check all that and post the results.

coonhound

Am having similar code 31. Just did the timing chain. It hard starts and is running too rough to time it.Seems like a fuel issue. No gas spraying out of the cylinder with a plug removed.Have done tdc several times don't think distributor placement is the issue. Put the ohm meter to the AFM and receive acceptable readings except one. Think its the last two connections in the haynes manual trouble shoot. No ohms on the big gold plug with the wire to the AFM. When it is running and begins its death cough you can hear the AFM slamming shut and gasping? As it has been sitting in the garage for a year after i changed the T-chain I turned it over without the distributor plugged to the coil to get some oil pressure and coat anything dry. Could an arc from the coil possibly screw up the AFM? Pulled the cap off nothing looks burnt or broken.

eastcoast

OK so I did a few tests staring with the AFM.
The fsm I have shows different pinouts on the ecu than I have. Mine is 10 18 14, my fsm says 26 16 12. The file says 90 - 95 4runner perhaps it is mislabled? Anyway I found a great write up here http://www.4crawler.com/4x4/CheapTricks/AFM/index.shtml
My Afm checked out except for the Static test E2-VS which is supposed to be 20 - 400 and mine is always between 560 - 885. And Dynamic test all is good except E2 - VS 20 - 400 closed = ~700. And plate open should be 20 - 1000 and mine is 1k - 1.4k
How do I check the voltages do I unplug the connector at the afm and measure them there? or do I measure it at the ecu?
Also I checked The TPS using this link http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml
And all voltages check out except for VTA - E2. I get no voltage whatsoever. I am measuring them at the connector while it is unplugged with the IGN on. So I measured it at the ECU and am getting 0.0V as well. I decided to plug the connector back in(TPS) and got 0.6V with the throttle closed. I do not know how to measure it at the connector while it is plugged in but it seems that it has to be plugged in to get voltage sent to it. Anyway I am going to get a AFM this weekend and see if that fixes the problem, and also do a compression test. I will post with the results.
Also as a side note When I have a front wheel off the ground and I spin it it will only do one free rotation. Same for both sides. is that normal? I am down to 12mpg now as well. Thanks again for everyones input!

eastcoast

*Fixed* here is the short version. I had a code 31 AFM, tested the AFM and it was faulty, and replaced it with a good one. Problem fixed. Thanks again for everones input!