RPM drops unexpectantly while driving on 2000 Nissan Altima

The car stopped working after I did an oil change before that the car was rough idling, took it to the mechanic we replaced the on board computer, replaced the engine, replaced the distributor, replaced the timing belt, did a tune up replaced all oil and liquids new spark plugs. The car ran fine for a week, but soon I noticed the RPM would unexpectedely drop. Eventually it would stop and the car would stop in its tracks. it stopped in the middle of the freeway, and the road. any information will help on what is the issue with this car.

by in Pasadena, CA on March 26, 2009
3 answers 1 comment
ANSWER by on March 26, 2009
It sounds like you need to take it back to the mechanic who did all the work. Possibly the computer was rebuilt and is defective ( not uncommon if it is not a factory unit ) Was it a brand new computer? Have the shop retrieve the code(s) and do a proper diagnostic of the problem. There should be a 1 year warranty for all the work you had done. I would do a sweep test of the Throttle Position Sensor on a labscope. They are notorious for a 'acting up' with out setting a code. They would also cause a 'fall on your face type of sympton'. Another thing to look at is the Ignition system. A Bad Cap and rotor and a bad igntion coil could cause theses symptons, as well as a defective distributor. I have seen Nissan Distributors fall flat on their face because the pick-ups in side get defective. They also will not set any codes, yet the car is basically undriveable. Have your mechanic check the spark output, it should be at least 40,000 - 50,000 volts. This will stress test the whole ignition system including the ignition module, cap, rotor, wires, coil and distributor. I assume that the plugs are brand new and are the factory recommended type.
COMMENT by on March 26, 2009
It was a rebuilt computer, warranty is only for 6 months we returned it and got another computer. My Mechanic tried it in his car, because he has the exact same year and model. I don't believe its the computer. The car no longer rough idles RPM stays steady until you give it gas while your on road the RPM drops totally kills the cars momentum and you kind fly forward in your seat. I don't know what item will affect the RPM directly from the engine. My mechanic took it to a Nissan dealership where they did a diagnostic and the dealership claimed to find nothing wrong with the car.
ANSWER by on July 28, 2010
Try the mass air flow sensor thats why my 93 was doing, its not real expensive if you order it from Ebay!
ANSWER by on January 25, 2011
must reprogram the trhotle it is a fly by wire system, it can be done manualy with out a computer, you will find the procedure on line for free