Mass Airflow, need Help!

I can rev the engine from the engine compartment
and there is almost a sec delay before the engine revs. Also there are
times during acceleration the engine runs smooth and then sometimes it
sputters. I am receiving trouble codes P-100(MAF sensor error circuit)
P-110(IAT sensor error circuit) and some random cylinder misfire codes.
The
cylinder misfire codes are most likely to be caused by the MAF or IAT
malfunctioning. I have changed and checked all wires and sparkplugs.
Since the error codes say sensor circuit there is most likely just a
bad wire somewhere???? I bought a MAF from a salvage yard(pick a part)
and
that did not solve the problem. Those *******s are expensive. Any
Advice????

JC wrote:
> I can rev the engine from the engine compartment
> and there is almost a sec delay before the engine revs. Also there
are
> times during acceleration the engine runs smooth and then sometimes
it
> sputters. I am receiving trouble codes P-100(MAF sensor error
circuit)
> P-110(IAT sensor error circuit) and some random cylinder misfire
codes.
> The
> cylinder misfire codes are most likely to be caused by the MAF or IAT
> malfunctioning. I have changed and checked all wires and sparkplugs.
> Since the error codes say sensor circuit there is most likely just a
> bad wire somewhere???? I bought a MAF from a salvage yard(pick a
part)
> and
> that did not solve the problem. Those *******s are expensive. Any
> Advice????


Also I tested the MAF Meter, using a voltimeter, and it tests out to be
fine.

I remember reading that computers sometimes test MAF sensors by
comparing them with TPS input. So maybe your TPS is no good and throws
computer into thinking MAF is no good. Test TPS with scope. Once I
tested a Ford Escort TPS with a meter and it appeared ok but with a
scope a fuzzy pattern showed no good.

On some cars the sensors have common powers or grounds also. Since
you have two codes maybe a component is pulling the reference voltage
to less than perfect and this will affect the other sensors like iat.
So measure the reference voltage going to MAF and IAT and make sure ok
and also check ground. Reference on most cars is around 5 volts and
ground should be close to zero. Although some cars have reference of 8
volts or other. If you have problem try disconnecting sensors one at
a time and remeasure, when you disconnect draining sensor it should go
back to 5 volts. It could be reference 5 volts from computer bad.

Check all your engine and battery ground connections for looseness and
corrosion..


"JC" > wrote in message
ups.com...
>I can rev the engine from the engine compartment
> and there is almost a sec delay before the engine revs. Also there are
> times during acceleration the engine runs smooth and then sometimes it
> sputters. I am receiving trouble codes P-100(MAF sensor error circuit)
> P-110(IAT sensor error circuit) and some random cylinder misfire codes.
> The
> cylinder misfire codes are most likely to be caused by the MAF or IAT
> malfunctioning. I have changed and checked all wires and sparkplugs.
> Since the error codes say sensor circuit there is most likely just a
> bad wire somewhere???? I bought a MAF from a salvage yard(pick a part)
> and
> that did not solve the problem. Those *******s are expensive. Any
> Advice????
>

Alright i checked the TPS using a Haynes Repair manual as reference
guide. The TPS tests fine. My truck, 98 4runner limited 3.4 V6 auto
113k, has a vortec(not karmen vortec) MAF with hotwires. The IAT is
embeded into the MAF on this model, so that is why I am getting the two
error codes. They say sensor circuit error. So it has to be something
to do with the wiring, an open or short, or the ECM...I am stumped
here. I have followed the damn wiring from the MAF very dilligently and
I cant find a problem. I guess I am about to gain access to the ECM and
tap the hell out of it while the engine is running to see if I have a
bad ECM.....Any other suggestions? Thx for help.

JC wrote:
> Alright i checked the TPS using a Haynes Repair manual as reference
> guide. The TPS tests fine. My truck, 98 4runner limited 3.4 V6 auto
> 113k, has a vortec(not karmen vortec) MAF with hotwires. The IAT is
> embeded into the MAF on this model, so that is why I am getting the
two
> error codes. They say sensor circuit error. So it has to be something
> to do with the wiring, an open or short, or the ECM...I am stumped
> here. I have followed the damn wiring from the MAF very dilligently
and
> I cant find a problem. I guess I am about to gain access to the ECM
and
> tap the hell out of it while the engine is running to see if I have a
> bad ECM.....Any other suggestions? Thx for help.


A model and engine, now we're talking! Tapping on the ECM will
probably tell you if you have a bad old GM computer, not so much on
your Toyota. Have you cleared the codes by removing the 15a EFI fuse
under hood? If so do they reappear immediately? A multiple code set
could be from someone previously turning the key on with the MAF
unplugged.

Having run a 3.4 with the MAF unplugged I can't say that it would delay
revving for one second as you originally posted. The ECM strategy
notes the problem as evidenced by the codes and uses other sensors to
compensate. They run better unplugged than they do with a whack'd
sensor plugged in.

But for something to look for that could set both codes:
On the MAF connector the 12 volt White/Blue wire and the Brown/Black
ground from the ECM are used to operate both functions of the MAF. A
problem with *either* wire could cause P0100 and P0110. And inspect
the ground wire that bolts to the left upper intake plenum area. It is
the shortest path to ground for most of the ECM sensors.

Incase you actually have another problem with coincidental meaningless
MAF codes, let me ask this: Has the timing belt been replaced lately?
If so, you might want to check crankshaft pulley bolt torque. If left
loose, the crank timing belt gear will eventually move and hog out its
keyway. The gear serves as the CKP sensor tooth wheel also, and that
upsets CKP timing info to the ECM as the crank gear rattles back and
forth out of check. This can cause bizarre power loss conditions more
akin to what you are describing without setting a code.
Toyota MDT in MO

When I first encountered this problem it was after a hard days drive
off in dirt/mud roads. I reset the codes and the car ran much better.
It runs much better when codes are reset but soon after(not immeditaly)
the check engine light comes back on and starts to run ****ty again.
When ever the codes are reset, during light acceleration the car runs
better. During light acceleration with the codes set the truck
hesitates and stumbles and I am forced to gas it to 3.2-4.5 rpms for
smoother acceleration....I understand that when the codes are reset the
computer runs of off a default, until it can set its own pattern,
right?

I have not replaced my belts recently and the car runs better with the
maf plugged in....I read in the Haynes Repair Manual to tap the ECM and
if it was bad it was cause the car to hesitate or possibly die. This
didn't make sense to me because it is a newer computer and I couldn't
understand what taping it would make it do. I was probally reading the
part referencing to the older ECMS on 94' models and below.

I am going to check the grounds and wires you specified more thourghly
right now.

I apperciate your help greatly........I want to solve this minor
problem on my own without taking the truck to a dealer/repair shop as i
do not trust them. Thx a billion...any more suggestions????

>I apperciate your help greatly........I want to solve
>this minor problem on my own without taking the
>truck to a dealer/repair shop as i do not trust them.
>Thx a billion...any more suggestions????

But you trust me? Oh well, that's a topic for a different time.

Now, the most common problem *caused* by the MAF on a 3.4 is a lean
code P0171, followed in likelyhood by a rich code P0174. So you're
problem doesn't make me think that you have a dirty MAF. But if you
did (after driving through mud and crap for a day) then you could try
cleaning the dirty elements inside the MAF. You can clean them off
with repeated shots of brake clean and air pressure. Remove MAF, turn
upside down, and look into it with a flashlight... you'll see two
elements in there I'm talking about. On the outside of the housing,
there's a bulbous little element that serves IAT duty. Clean it the
same way (even though that won't help much you might as well)
Toyota MDT in MO (Dealer)

Yeah bro I cleaned the MAF, using alchoal. I did that initially and
nothing happend. Then I relized the code I was getting was the sensor
circuit error so that prompted me to pull out the voltimeter to test
the MAF as described to do in the Haynes manual. The voltimeter test
registers the right ohmage so I am pretty sure the MAF is not the
problem. I also bought a working MAF from a salvage yard and that did
not solve the problem, out 120 bucks there.....