Driveability problem at e-way speeds car will suddenly not accelerate or maintain speed, I stop and start going again, it will go for a few minutes and do it again. Its very hard to drive on e-way. I've changed plugs, fuel/air filter ,oil/filter,bottle of injector cleaner. old codes p0420 left bank below theshold.for..150,000

Step One: How to Prepare Your Vehicle

• Have the fuel tank between 30 and 70 percent full. Some systems, especially the EVAP system, need to have a specific level of fuel in order for the tests to be trusted. If the fuel tank is near empty or completely full, many of the basic tests will not run at all.
• The vehicle must also have a good alternator and a strong battery. If you have to occasionally jump-start your vehicle, all of the memory from the powertrain control module (PCM) is erased, which includes the data that accurately tracks the results from various stages of the Drive Cycle. Also, if the battery is weak or undercharged, some of the most important tests will never run.
• The vehicle must sit overnight, or for at least eight hours, in an environment that is less than 90° F. The engine temperature needs to match the air temperature in order to establish an accurate baseline for the testing. If the outside temperature is over 90° F, the fuel is too volatile and the EVAP system won't even try to run its tests, though some of the other emissions systems may run their tests.
• The keys must be out of the ignition and all of the doors must be closed while the vehicle sits over night because many of the onboard computers "boot up" when the keys are in the ignition. Also, many of the onboard computers still run until all of the doors are closed after the vehicle is shut off and the keys are removed.

Step Two: The Cold Start

• Start the vehicle and let it idle for two to three minutes in Park or Neutral. While it is idling, turn on the head lights, heater/defroster, and rear defroster for a three to five minute warm-up phase. Let the idle speed settle down to near the normal speed.
• Next, put the vehicle in gear and drive through city streets at about 25 mph. Go up to about 35 to 40 mph a few times before slowing down to stop. Don't roll through the stop; be sure the car is really stopped, just like you learned in driving school. Accelerate from each stop in a normal fashion-not overly conservative, but not like you are competing in a drag race either.

Step Three: A Short Freeway Trip

• After the vehicle has been cold started and driven for a few miles on city streets, the next step is to take it on a short freeway trip.
• Enter the freeway on-ramp and allow enough room with respect to other vehicles so that you can do a 1/2 to 3/4 throttle acceleration up to freeway speed.
• When you have accelerated up to around 60 mph and have safely merged into the flow of traffic, stay in the slow lane and maintain a steady speed of 55 to 60 mph for a minimum of five miles. Please use the cruise control to help you maintain speed.
• Find a nice, long off ramp to exit from the freeway. As you exit, take your foot off of the accelerator and let the vehicle coast down until it stops under its own power as you complete your exit from the freeway. Do not use the foot brake and do not shift gears until the very end of this "coast down" phase.

• Step Four: More City Driving
  • After you have completed the freeway trip, drive through the city streets for a repeat of the second part of Step Two.
  • Go up to about 35 to 40 mph a few times and then maintain a city speed of 25 mph before slowing down to stop. Again, don't roll through the stop and make sure to accelerate normally.
  • Pull in to a parking place and let the engine idle for one to two minutes and then shut it off.
  Step Five: Have your Readiness Monitors Checked and Verified
  
  • Drive your vehicle to your regular shop and have them re-check your readiness monitors, present codes, and pending codes. They should do this as a courtesy and for free.
  • If all of your monitors are "ready" and there are no present or pending codes, then your vehicle has been properly repaired and is ready for an emissions inspection and for normal driving.
  
  

Sounds like the vehicle speed sensor is bad. If the computer does not see the speed your going all sorts of driveability issues can arise

How to Perform a Basic Drive Cycle

Step One: How to Prepare Your Vehicle

• Have the fuel tank between 30 and 70 percent full. Some systems, especially the EVAP system, need to have a specific level of fuel in order for the tests to be trusted. If the fuel tank is near empty or completely full, many of the basic tests will not run at all.
• The vehicle must also have a good alternator and a strong battery. If you have to occasionally jump-start your vehicle, all of the memory from the powertrain control module (PCM) is erased, which includes the data that accurately tracks the results from various stages of the Drive Cycle. Also, if the battery is weak or undercharged, some of the most important tests will never run.
• The vehicle must sit overnight, or for at least eight hours, in an environment that is less than 90° F. The engine temperature needs to match the air temperature in order to establish an accurate baseline for the testing. If the outside temperature is over 90° F, the fuel is too volatile and the EVAP system won't even try to run its tests, though some of the other emissions systems may run their tests.
• The keys must be out of the ignition and all of the doors must be closed while the vehicle sits over night because many of the onboard computers "boot up" when the keys are in the ignition. Also, many of the onboard computers still run until all of the doors are closed after the vehicle is shut off and the keys are removed.

Step Two: The Cold Start

• Start the vehicle and let it idle for two to three minutes in Park or Neutral. While it is idling, turn on the head lights, heater/defroster, and rear defroster for a three to five minute warm-up phase. Let the idle speed settle down to near the normal speed.
• Next, put the vehicle in gear and drive through city streets at about 25 mph. Go up to about 35 to 40 mph a few times before slowing down to stop. Don't roll through the stop; be sure the car is really stopped, just like you learned in driving school. Accelerate from each stop in a normal fashion-not overly conservative, but not like you are competing in a drag race either.

Step Three: A Short Freeway Trip

• After the vehicle has been cold started and driven for a few miles on city streets, the next step is to take it on a short freeway trip.
• Enter the freeway on-ramp and allow enough room with respect to other vehicles so that you can do a 1/2 to 3/4 throttle acceleration up to freeway speed.
• When you have accelerated up to around 60 mph and have safely merged into the flow of traffic, stay in the slow lane and maintain a steady speed of 55 to 60 mph for a minimum of five miles. Please use the cruise control to help you maintain speed.
• Find a nice, long off ramp to exit from the freeway. As you exit, take your foot off of the accelerator and let the vehicle coast down until it stops under its own power as you complete your exit from the freeway. Do not use the foot brake and do not shift gears until the very end of this "coast down" phase.

Step Four: More City Driving

• After you have completed the freeway trip, drive through the city streets for a repeat of the second part of Step Two.
• Go up to about 35 to 40 mph a few times and then maintain a city speed of 25 mph before slowing down to stop. Again, don't roll through the stop and make sure to accelerate normally.
• Pull in to a parking place and let the engine idle for one to two minutes and then shut it off.

Step Five: Wave your Readiness Monitors Checked and Verified

• Drive your vehicle to your regular shop and have them re-check your readiness monitors, present codes, and pending codes. They should do this as a courtesy and for free.
• If all of your monitors are "ready" and there are no present or pending codes, then your vehicle has been properly repaired and is ready for an emissions inspection and for normal driving.
• If your monitors are not ready, please click here for more information.

How to Perform a Basic Drive Cycle

Step One: How to Prepare Your Vehicle

• Have the fuel tank between 30 and 70 percent full. Some systems, especially the EVAP system, need to have a specific level of fuel in order for the tests to be trusted. If the fuel tank is near empty or completely full, many of the basic tests will not run at all.
• The vehicle must also have a good alternator and a strong battery. If you have to occasionally jump-start your vehicle, all of the memory from the powertrain control module (PCM) is erased, which includes the data that accurately tracks the results from various stages of the Drive Cycle. Also, if the battery is weak or undercharged, some of the most important tests will never run.
• The vehicle must sit overnight, or for at least eight hours, in an environment that is less than 90° F. The engine temperature needs to match the air temperature in order to establish an accurate baseline for the testing. If the outside temperature is over 90° F, the fuel is too volatile and the EVAP system won't even try to run its tests, though some of the other emissions systems may run their tests.
• The keys must be out of the ignition and all of the doors must be closed while the vehicle sits over night because many of the onboard computers "boot up" when the keys are in the ignition. Also, many of the onboard computers still run until all of the doors are closed after the vehicle is shut off and the keys are removed.

Step Two: The Cold Start

• Start the vehicle and let it idle for two to three minutes in Park or Neutral. While it is idling, turn on the head lights, heater/defroster, and rear defroster for a three to five minute warm-up phase. Let the idle speed settle down to near the normal speed.
• Next, put the vehicle in gear and drive through city streets at about 25 mph. Go up to about 35 to 40 mph a few times before slowing down to stop. Don't roll through the stop; be sure the car is really stopped, just like you learned in driving school. Accelerate from each stop in a normal fashion-not overly conservative, but not like you are competing in a drag race either.

Step Three: A Short Freeway Trip

• After the vehicle has been cold started and driven for a few miles on city streets, the next step is to take it on a short freeway trip.
• Enter the freeway on-ramp and allow enough room with respect to other vehicles so that you can do a 1/2 to 3/4 throttle acceleration up to freeway speed.
• When you have accelerated up to around 60 mph and have safely merged into the flow of traffic, stay in the slow lane and maintain a steady speed of 55 to 60 mph for a minimum of five miles. Please use the cruise control to help you maintain speed.
• Find a nice, long off ramp to exit from the freeway. As you exit, take your foot off of the accelerator and let the vehicle coast down until it stops under its own power as you complete your exit from the freeway. Do not use the foot brake and do not shift gears until the very end of this "coast down" phase.

Step Four: More City Driving

• After you have completed the freeway trip, drive through the city streets for a repeat of the second part of Step Two.
• Go up to about 35 to 40 mph a few times and then maintain a city speed of 25 mph before slowing down to stop. Again, don't roll through the stop and make sure to accelerate normally.
• Pull in to a parking place and let the engine idle for one to two minutes and then shut it off.

Step Five: Wave your Readiness Monitors Checked and Verified

• Drive your vehicle to your regular shop and have them re-check your readiness monitors, present codes, and pending codes. They should do this as a courtesy and for free.
• If all of your monitors are "ready" and there are no present or pending codes, then your vehicle has been properly repaired and is ready for an emissions inspection and for normal driving.
• If your monitors are not ready, please click here for more information.

You overfilled the tank and screwed up the fuel vent canister. Usually the car will not run, dies while idling, or surges if you try to drive, also if you try to fill up again you might find it difficult to fill your tank fast because the canister is not venting the tank

Might be the throttle position sensor.

The automatic idle speed control system has lost its adaptive idle learning due to the dead battery. To help to correct this in the short term run the engine at 2000 RPM until warm, then back down to 1500 RPM for 3 minutes, then 1000 RPM for 3 minutes, then let it idle for 5 minutes, this should get the system to a point in the idle learn that it doesn't stall out, then drive it for 20 miles under varied conditions of highway and stop and go and low speed operation, that should get all to work again. If you still have problems you will need to have the system scanned to see what is going on that is causing a stall. Also add fresh fuel, gas goes bad in about 3 months. Use the recommended grade of fuel.

I have a 96 Grand Marquis with a similar problem. Also on the highway it would just conk out on me suddenly, almost felt like I was hitting the brakes, then it would pick up again. Eventually got to the point where it was stalling out on the highway and at red lights. One day it wouldn't start. Mechanic said the fuel filter was clogged solid. It has run well but every once in awhile still stalls out on me. From talking with other Grand Marquis owners and the mechanic the Mass Air Flow sensor may be to blame. He wanted to charge me $400 but I found the part online for about $85.

Yes, the sensor is the first thing you should replace.

Try this relearn procedure hopefully it will help

Vehicles equipped with engine or transmission computers may require a relearn procedure after the vehicle battery is disconnected. Many vehicle computers memorize and store vehicle operation patterns for optimum driveability and performance. When the vehicle battery is disconnected, this memory is lost. The computer will use default data until new data from each key start is stored. As the computer memorizes vehicle operation for each new key start, driveability is restored. Vehicle computers may memorize vehicles operation patterns for 40 or more key starts. Customers often complain of driveability problems during the relearn stage because the vehicle acts differently then before being serviced. Depending on the type of vehicle and how it is equipped, the following complaints (driveability problems) may exist:

Harsh Or Poor Shift Quality
Rough Or Unstable Idle
Hesitation Or Stumble
Rich Or Lean Running
Poor Fuel Mileage

These symptoms and complaints should disappear after a number of drive cycles have been memorized. To reduce the possibility of complaints, after any service which requires battery power to be disconnected, vehicle should be road tested.

Vehicle Preparation

Ensure all components are connected. Ensure transmission fluid level is correct. Warm engine to normal operating temperature. If vehicle has been repaired, perform KOEO and Continuous Memory Code Self-Test and ensure fault codes are not present.

Computer Relearn Procedures

Idle Relearn Procedure

Place automatic transmission in Park or manual transmission in Neutral position. Ensure the emergency brake has been set and all accessories are turned off. Start engine and bring to normal operating temperature. Allow manual transmission vehicle to idle in Neutral for one minute. Allow automatic transmission to idle in Neutral for one minute and then to idle in Drive for one minute. Once initial relearn is complete, process will be completed during normal driving. Always complete the procedure before returning the vehicle to the customer.

Drive Cycle Test (AOD-E, AXOD & AXOD-E TRANSAXLES)

With transmission gear selector in Overdrive, moderately accelerate vehicle to 50 MPH for a minimum of 15 seconds. Transmission should be in 4th gear. While holding speed steady, lightly apply and release brake for about 5 seconds. Stop and park vehicle for a minimum of 20 seconds with transmission gear selector in Drive. Repeat procedure 5 times. Always complete the procedure before returning the vehicle to the customer.

Drive Cycle Test (E4OD)

With transmission gear selector in Drive, press Overdrive Cancel Switch (LED should light). Moderately accelerate vehicle to 40 MPH for a minimum of 15 seconds (30 seconds above 4000-ft. elevation) Transmission should be in 3rd gear. While holding speed steady, press Overdrive Cancel Switch (LED should go off) and accelerate from 40 MPH to 50 MPH. Transmission should shift from 3rd gear to 4th gear. Hold speed steady for 15 seconds. While holding speed steady, lightly apply and release brakes enough to turn brake lights on. Maintain 50 MPH for about 5 seconds. Stop vehicle for a minimum of 20 seconds with transmission gear selector in Drive. Repeat procedure 5 times. Always complete the procedure before returning the vehicle to the customer.