1996 f150 5.8 4x4 idler controll,fuel Syestem is good Changed throttle sensor,mass .Whole distributor,wires,Plugges.Engine will run ruff with mass unplugged & soon after reconnecting the mass,go dead

I would suspect the mass air flow sensor. It is located on the passenger side of the throttle body (under the air cleaner). These are very poorly made and fail often without throwing any codes. Here's a link of the part. Some emission parts for the 1997 pickup are different depending on the month of manufacture so make sure you get the correct part.
http://www.aipelectronics.com/index.php/mass-air-flow-sensor-meter-1996-2004-nissan-pickup-frontier-and-xterra.html?Tracker_ChannelID=28&Tracker_CustomerID=319&Tracker_variantid=419611&gclid=CLPJs_Wr4b4CFVJefgodmIUANQ

clean the idler on the intake and also clean the throttle sensor, it would also be best to change the air filter and clean the maf sensor. Idler does more than just idle vehicle it controls low revs, and drop down from reves. throttle sensor tell ecu what air to add to the fuel. and the MAF tells ecu how much air is coming into the intake. also check for broken cracked vacuum lines.

This could be air or fuel, if you are getting a mass air flow code then make sure there are no vacuum leaks around the intake also if the distributor is in wrong depending on how far off it is it could run but will run bad and will stall out, did you mark the distributor housing and also where the rotor was pointing as it is very important that the distributor rotor is point in the same spot as it was coming out if not then you will need to set the engine at top dead center and then locate the #1 cap location and install the dist rotor to be pointing to that wire,,top dead center is with #1 cylinder at the top of the compression stroke, make sure before you do that that there are no leaks try to keep it running by holding the gas pedal while someone look for a vacuum leak, you will hear a hissing sound for a vacuum leak, good day.

The only part that would come to mind after all of this would be the fuel pump relay. This is located on the fire wall on the drivers side of the car. When that goes bad it does not allow for adequate fuel to cycle through.The other thing would be timing. You need fuel air and spark for the vehicle to fire. After all the test and after replacing the fuel pump relay. I would do a compression and a leak down test. Are you sure that the timing did not jump a gear? You can also look and test the IAC (Idle Air Control) or the MAF (Mass Air Flow Sensor). Also do a test to check fuel pressure. The last Corvette that I worked on personally that had this issue it turned out to be the Fuel Pump Relay. Good luck let me know if you have any further questions.

Sounds like throttle position sensor or mass air flo sensor.Both of these can be checked by hooking up to computer.You dont want to ramdomly start changing sensors can get costly.

I would check your spark plug wires as well. One could be faulty. But if the RPM's are fluctuating up and down, theres a good chance that the engine isn't getting a consistent air flow. Some things to check are your intake, Mass Airflow Sensor, Throttle body, and air filter. On the intake, check the hose that goes from your air filter to the engine, make sure there aren't any holes or anything abnormal to it. As far as your Mass Airflow Sensor, some times if you go without changing your air filter for a good while, debris and dirt will pile up on the sensor causing it to send incorrect signals to the computer for the engine making it take in too much or too little air to the engine. You can solve this by getting a can of MAF sensor cleaner and following the instructions on the can. BE VERY CAREFUL if you choose to pursue this troubleshooting option because that sensor is very sensitive and can break easily causing you to have to buy a whole new sensor. Buying a new sensor should be a last option after everything else has been tried. As far as the throttle body, make sure that the wire that controls the air intake isn't broken or frayed, which would cause it to operate incorrectly. Additionally, check your Throttle Positioning Sensor, and Idle air control valve. The Throttle positioning sensor tells the computer how much air to allow into the engine when accelerating or idling, and the Idle Air control valve does a similar function by regulating how much air flows through the engine when in idle (rest). And finally your air filter. It's good to change that out pretty much every oil change to maintain a clean airflow to the engine, which is a huge factor to its performance and fuel economy. Further troubleshooting options would involve your spark plugs and spark plug wires, you may have a faulty spark distributor. Its that box that the other end of the wires are connected to, it is what sends out the current to the spark plugs. And after that if it gets this extensive, you may have a problem with your fuel lines or fuel distributor. Most likely it has to deal with air flow because I had to solve a very similar problem on my friend's Mazda Protoge. If you have a check engine light, next time you get the vehicle to start, bring your car to an auto parts store and see if they can read the codes that the computer is putting off that signals what the problem is. It should give you the exact location of the problem with your vehicle. I hope this bit of information is useful to you, and I wish you good luck.

check for vacuum leaks, check distributor cap and rotor button, clean or replace as necessary. Use quality injector cleaner.

Check the fuel filter, it might be clogged.

Hello,
your problem appears to be the idle control motor located on the air intake manifold it is a small motor that goes bad quite often. Other items that can cause this is a bad /clogged air filter or a tune up (spark plugs and wires), or clogged fuel injectors. to clean the injectors you can buy a container of fuel system cleaner and pour it into the gas tank and as you drive it cleans the system.

Once the fuel system is cleaned via a tankful of cleaner & gas then the idle controller motor would be next on the list to be replaced.

Good Luck !
Rich Lilja

my 1988 mazda 626 starts okay then dies everytime it idles down to normal idle speed. i replaced the throttle control sensor and the mass air sensor. i replaced the rotor in the distributor but is still dies. if you throttle up to about 1500 rpm it keeps running. any ideas???