Ok so lets first diagnose the car. There is a need to verify the fuel system. As these are returnless always verify everything. As stated you could throw brand new off the line wngine in and if parts hanging on it are junk your pissing in the wind.
P0068 means that the Powertrain Control Module (PCM) has detected an excessive degree of variation in the input voltage signal from the throttle position sensor (TPS) as compared with voltage input signals from the mass air flow (MAF) sensor and the manifold air pressure (MAP) sensor. The PCM reads and calculates these individual engine drivability sensor signals and then compares them to help develop fuel delivery and ignition timing strategy. The PCM also utilizes this information to ensure that the fuel-to-air ratio remains constant, controllable, and within acceptable limitations. If the detected voltage values of these three sensors (triangulated) fail to coincide with programmed desired parameters, over a specific period of time or engine revolutions, a diagnostic trouble code will be stored and a malfunction indicator lamp will likely be illuminated.The most frequent contributors to this code being set are large vacuum leaks as a result of cracked, broken, or otherwise collapsed vacuum lines and hoses. Other sources of vacuum leaks include defective intake and throttle body gaskets, EGR valve and gasket malfunctions, and vacuum operated component (brake boosters, etc.) defects. Other possible causes could include a cracked or disconnected air intake pipe, clogged air filter, a faulty TPS, MAF, and/or MAP sensor, or a defective PCM.
P0069 The manifold absolute pressure (MAP) sensor is used to measure engine load. The powertrain control module (PCM) sends the MAP sensor a reference voltage and the sensor varies the voltage according to manifold vacuum. The PCM then uses this information to adjust ignition timing and fuel delivery.
Vacuum and pressure are inversely proportional (when vacuum goes up, pressure goes down). Because of this, the MAP sensor is able to measure the pressure in the intake manifold to gauge vacuum. Manifold vacuum is a good indicator of engine load. With the engine off, manifold pressure and atmospheric (barometric) pressure are the same. With the engine running, the movement of the pistons and restriction of the throttle plates create vacuum (reduce pressure). When the engine is under heavy load at wide open throttle (WOT), vacuum is nearly zero. At this time, engine pressure and atmospheric pressure are almost the same.
Depending on the elevation, barometric pressure is usually between 28 to 31 inches of mercury (Hg). By comparison, engine vacuum at sea level is between 17-22 in-Hg. This drops approximately 1 in-Hg for every 1000 ft. of elevation. On some vehicles, when the engine is first started, the PCM looks at the MAP sensor to determine barometric pressure. There are other vehicles, however, that use a dedicated BARO sensor. Others still use a combination BMAP sensor.
There are two types of MAP sensors: analog and frequency. The analog type uses a diaphragm and is connected to the intake manifold by a vacuum line. The sensor monitors the movement of the diaphragm and sends a corresponding analog signal back to the PCM. This type of sensor will have three wires: reference, signal and ground. The other type of MAP sensor is the digital, or frequency type, which produces a digital voltage signal instead of an analog signal.
analog-map-sensor
A cut away of an analog MAP sensor
(Courtesy: autozone.com)
As was mentioned, some vehicles use an independent BARO sensor. These devices are designed to measure only barometric pressure. The BARO sensor is similar to the MAP sensor in design but is more sensitive to changes in atmospheric pressure.
The code P0069 stands for manifold pressure/barometric pressure correlation. The PCM compares BARO sensor and MAP readings at idle. If the difference between the two is greater than specified, the PCM will set a diagnostic trouble code (DTC).
MAP sensor circuit problem
BARO sensor circuit problem
Faulty MAP sensor
Faulty BARO sensor
Faulty PCM
