3.9 engine is idling rough but smooth when accelerating or driving. If I put in neutral it's still rough. Have 250000 thinking maybe injectors? Or where do I start?

SOURCE: ford f350 6.0L Turbo runs rough

Still sounds like there is a fuel issue. I would check the obvious. Check the Air filter and fuel filter and water seperator. Debris could have gotten into the new injector, which also could have upset the other injector. Get the exact code from the dealer your truck experianced.

SOURCE: rough idle / engine surges until power is applied

Sounds like a possible vaccume hose leak?

Marvin

• 85242 Answers
• Posted on Feb 18, 2009

SOURCE: ROugh idle

there are 2 things that usually cause this, one is a dirty intake idle control valve and the other is hard engine mounts, I would say that both most likely apply to your car. try cleaning the intake with the following procedure from Ford.
Here is the most common cause of surges and stalls and low idle rough idle, it is the idle speed control air-bypass valve and throttle valve (IAC for short), they get full of gunk 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: 1996 FORD CONTOUR 4CYL ROUGH IDLE ROUGH ACCELERATION

no problem. If you are getting that low of voltage on a load then you might want to test the alternator as well to make sure it is running at capacity.

SOURCE: hesitates on acceleration

Does the car always hesitate during acceleration? If it ALWAYS struggles when it starts or ALWAYS hesitates on acceleration then I would say the issue is fuel delivery. If the problems are more intermittent and come-and-go then it could be an electrical issue.

I would start by changing the fuel filter. Changing plugs, wires, cap, and rotor are all good things to do as your budget will allow. I doubt you will have to change your injectors.

If you end up replacing any rubber fuel line, be sure to use the high-pressure stuff made for use on fuel injected cars.

I hope this helps! -Nick