When the car starts, it idles smoothly but after about 30 seconds the idle slows down to about 800 rpm and slightly runs rough and then eventually runs rough and stalls. The car starts back up and goes through the same routine. After driving and stopping at a red light for example, the car runs smoothly for a few seconds and progressively runs rough and stalls.

SOURCE: Rough idle

I took mine in to change the plugs and they said there are four O2 sensors in the fuel mixture system and two were bad. I didn't replace them since they were a little pricey ($500 to replace both) and I have 103,000 on the car. Has very similar roughness and occasional oscillations, but no stalling. Hope this helps.

Marvin

• 85242 Answers
• Posted on Nov 12, 2008

SOURCE: rough idle

Have you had the throttle valve cleaned?

Here is the most common cause of surges and stalls, it is the idle speed control air-bypass valve and throttle valve, they get full of gunk over the miles and cause idle issues (stalls) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

SOURCE: rough idle stalls at low rpm's

check your transmission fluid,the motor will stall when fluid is low

Marvin

• 85242 Answers
• Posted on Apr 29, 2009

SOURCE: 1996 mercury mystique stalls when I stop a red light

I am a Ford tech (35 years) and this is the cause of the problem in about 90% of the cars I see with this problem.
Here are some of the causes of surges, stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

SOURCE: 2003 Sport Trac runs ok above 1000 rpm's but if

scan it check the egr valve.make sure its not staying open.