list of things to check and some questions
- the IAC valve might be giving the correct readings but is it stiff or sticking?
- does any of this happen when it is warm outside as in during summer?
- when you blip the throttle the car will stumble because of the sudden rush of air and the injectors firing to make up then suddenly no air and a too rich scenario. but it should recover quickly afterwards and not waver.
- can you take a picture of all the spark plugs lined up from the front of the engine to the back? This is so we can see if they are shiny black, wet, dull black, white, or some mix of those. Shiney black we want to avoid as it means burning oil, wet black usually means burning lots of oil, white I do not suspect since you have a manifold leak, dull black would be the oxygen sensor picking up a lean condition due to the manifold leak introducing clean air and tricking it. This will tell the computer to run richer.
- how often do you need to add a quart of oil?
- are you warming up and running for a while then restarting right away as in seconds or less of off time? or is this more like grabbing a coffee and returning off time?
- can you take an ohm reading off your oxygen sensor? this will tell us if it sees a lean or rich state. specifically when the engine stumbles after starting.
The sudden dropping low after starting could be another reason to suspect the exhaust leak. once the car starts it will have higher revs. This creates more exhaust flow. Once it starts dropping to idle the flow of exhaust will create a vacuum pulling clean air in. This trips the computer to go rich causing the engine to stumble for a little bit. So far this is what it is sounding like.
Well the constant building speed can create internal pressure on the manifold which would push exhaust gasses out rather than suck clean air in. This would give the oxygen sensor a proper reading. This would cause the computer to give the proper amount of fuel to achieve balanced stoichiometry.
Once you drop the gas to idle the exhaust gasses that were leaving at a high rate of speed suddenly are not being pushed any longer, you can think of how a toilet flushes, this creates a vacuum which is pulling clean air into the manifold. this tricks the oxygen sensor into thinking you are lean telling the computer this causes the computer to richen up the fuel charge. This causes the extra long recovery after suddenly letting off the gas.
You can see this for yourself with a smoke machine. Blow the smoke at the leak and increase the RPMs steadily and you should see the smoke moving away from the leak. Letting off suddenly should jerk the smoke back towards the leak.
it looks like the 2 left sparkplugs were the new changed ones. about how many miles ago? the middle right one is dull and a little sooty looking which may be rich but not burning oil. The far right one is oil burning.
whenever looking at spark plugs you really want them to all come out a brown. This means there is some carbon there and some lean-ness but it is sitting right on the edge of both.
General rule is:
- white = lean
- dull black = rich
- shiny black = oil burning
- brown = happy and balanced
The sucking sound you hear near the throttle body is probably air trying to get around a closed or just cracked open throttle valve. Is the throttle body sitting before or after the mass airflow sensor? If it is before a leak shouldn't matter but if it is after a leak can cause a lean condition. if you want to check for leaks around there take a torch but don't light it just open its valve and point it near things and see if the RPMs rise. BE VERY careful this can cause fires and explosions use common sense or you will be sorry also wear protection and have a fire extinguisher ready. This does have the potential of catching your car on fire!
the o2 sensor should read all over the place between .9 and .1 volts. you sure your volt meter is working properly? If it is not grounded out it will read 0 telling the engine you are permanently too lean so it will go full rich. If grounded out it will still not work because they need lots of heat for it to produce voltage. here is more information on O2 sensors. The part you are going to be most interested in is.
How it Works
The O2 sensor works like a miniature generator and produces its own
voltage when it gets hot. Inside the vented cover on the end of the
sensor that screws into the exhaust manifold is a zirconium ceramic
bulb. The bulb is coated on the outside with a porous layer of
platinum. Inside the bulb are two strips of platinum that serve as
electrodes or contacts.
The outside of the bulb is exposed to the hot gases in the exhaust
while the inside of the bulb is vented internally through the sensor
body to the outside atmosphere. Older style oxygen sensors actually
have a small hole in the body shell so air can enter the sensor, but
newer style O2 sensors "breathe" through their wire connectors and
have no vent hole. It's hard to believe, but the tiny amount of space
between the insulation and wire provides enough room for air to seep
into the sensor (for this reason, grease should never be used on O2
sensor connectors because it can block the flow of air). Venting the
sensor through the wires rather than with a hole in the body reduces
the risk of dirt or water contamination that could foul the sensor
from the inside and cause it to fail. The difference in oxygen levels
between the exhaust and outside air within the sensor causes voltage
to flow through the ceramic bulb. The greater the difference, the
higher the voltage reading.
An oxygen sensor will typically generate up to about 0.9 volts when
the fuel mixture is rich and there is little unburned oxygen in the
exhaust. When the mixture is lean, the sensor's output voltage will
drop down to about 0.1 volts. When the air/fuel mixture is balanced or
at the equilibrium point of about 14.7 to 1, the sensor will read
around 0.45 volts.
When the computer receives a rich signal (high voltage) from the O2
sensor, it leans the fuel mixture to reduce the sensor's reading. When
the O2 sensor reading goes lean (low voltage), the computer reverses
again making the fuel mixture go rich. This constant flip-flopping
back and forth of the fuel mixture occurs with different speeds
depending on the fuel system. The transition rate is slowest on
engines with feedback carburetors, typically once per second at 2500
rpm. Engines with throttle body injection are somewhat faster (2 to 3
times per second at 2500 rpm), while engines with multiport injection
are the fastest (5 to 7 times per second at 2500 rpm).
The oxygen sensor must be hot (about 600 degrees or higher) before it
will start to generate a voltage signal, so many oxygen sensors have a
small heating element inside to help them reach operating temperature
more quickly. The heating element can also prevent the sensor from
cooling off too much during prolonged idle, which would cause the
system to revert to open loop.
Heated O2 sensors are used mostly in newer vehicles and typically have
3 or 4 wires. Older single wire O2 sensors do not have heaters. When
replacing an O2 sensor, make sure it is the same type as the original
(heated or unheated).