Yes it will rear the AFM in open loop, but does not use the O2 sensors until the engine reaches operating temperature and it goes into closed loop. It will use the AFM, TPS, and RPM to calculate AFR based on standard fuel maps. The fact that it runs fine while in open loop, and has no throttle problems leans towards an O2. If the AFM has an issue it normally would be like that all the time, same if it were an issue with the TPS.

Keep in mind this is generally the case, Being a Diagnostic Technician, I have seen my share of things that defy logic, and normal failures.

I am going to do some testing in my truck just for the hell of it, and I never recommend throwing parts at problems, check them first then fix it. But if your 02 sensors are original, or have a ton of miles on them, they are likely due to be replaced anyways. If anything it will help the overall efficiency of the engine.

Dave

 

My 92 had a similar problem. Turned out to be the MAF. I found it by tapping on it with a screwdriver while engine was idling. The engine would stumble and die.

 

The good old "Wiggle and Tap test"

 

Mine is probably the o2 sensor cause I don't have one lol. The p.o did this. He replaced the manifold with one that didn't have the bung for the o2 sensor and the plug is just hanging there. I'm getting another manifold tonight and o2 sensor. I will let u know if this is my problem. My afm tested fine according to the FSM but I'm still getting the code for it. I have rest it it too and it's still there. Hopefully the new manifold and o2 sensor will fix the bogging.

 

Only buy a Denso direct fit O2! Don't waste your money on Bosch or anything else. Our trucks are very picky. You can buy the correct Denso sensor off eBay for 40-50 bucks.

 

Its got one in it already and its a denso so I'm going to try it out first and see what happens. Thanks for the heads up

 

Test the wires at the ECM, voltage and resistence checks per the FSM computer section.

 

I tested it there and it looks good too. would not having an o2 in make the ecu think there is something wrong with the afm?

 

Yoyaslave: had any luck with yours? I was going to put in my new manifold last night but I dropped it and broke the o2! If aint one thing its another lol. So I ordered another one today from advance auto, there like $30 with a $10 rebate for the denso.

 

No. You either have a wiring issue, or an afm that is bad.

 

Even tho it tested good, it could still be bad? After I get the o2 in I'm going to put my buddies afm in and see what happens. Thanks for all ur help by the way.

 

Which code exactly are you getting persistently?

 

2,5&8

 

I installed my manifold and new o2 sensor this morning and...... NO MORE BOGGING . . I took out the EFI fuse and cleared the codes and drove it about 5 miles and got back home and checked for codes again and nothing so far. It ran really good but i did notice a miss ( engine stumbles for just a second) around 2500 rpms. . Im still going to put my buddies afm in tonight when he gets home and see if it runs even better. Thanks for every ones help

 

Dropped your manifold!? Ahh!! I'm really glad that fixed your problem. I haven't had time to test my TPS yet (though it's on my list). I put the AFM from our other Toyota into mine and it's running better (less drop in power and more acceleration before the drop). I ordered the O2 sensor a couple days ago and it's here so I'm going to plug her in and see how she does. Hopefully this was my problem as well, fingers crossed(: Thanks for the update!!

 

Good luck!

 

O2 didn't work.

 

Do I need to take out my efi fuse and clear codes??

 

Yes. What do you mean it didn't work?

 

I replaced it and it ran better for awhile but then it cut out as usual.