QuestionQUESTION: My husband has replaced both the Crank Positon and Ouptut Position Sensors, because of hestitaning and stalling problem. The car is still giving me problems. The RPM's continue rise and fall causing the car to jerk forward when I am driving it. No check engine light is going so we have no clue where to look. Anyone one have any ideas?
ANSWER: This could be one of the following problems:
-- Break in bellows between air cleaner and engine.
-- Air bellows only loosely attached to throttle body, allowing it to come loose.
-- Throttle position sensor issue, causing the transmission control module to command shifts based on the erroneous readings.
-- Internal transmission problem.
If you don't see any visual evidence of a problem, I'd recommend taking the vehicle to a competent and reputable shop. A scan tool will likely be needed for proper diagnosis. With this tool, the mechanic can monitor the transmission and engine sensor data and more easily determine where the problem may lie.
---------- FOLLOW-UP ----------
QUESTION: Without a check engine lit how can the scan tool detect the problem?
AnswerThere may be a trouble code stored even if the check engine lamp isn't on. A simple code reader can tell you whether this is the case.
A scan tool doesn't so much detect problems, but rather allows the technician to read pertinent data. In this case, after driving the car and determining whether it is a transmission or engine performance issue, the technician might be interested in data such as the air flow sensor voltage and throttle position sensor voltage.
