Code P0171, with idle surge?

JACKIEMCNTY510

MEMBER
2003 MITSUBISHI DIAMANTE
3.5L
V6
AUTOMATIC
200,784 MILES

I recently changed the gasket for the air intake manifold and the valve cover myself which I've done plenty of times before without any problems until now. I got a check engine light on p0171 lean code and the engine surges at idle. I've checked for vacuum leaks, found one and fixed it, erased the code, but it popped back up. I did try unplugging the MAF sensor which stopped the surging. So, does that mean I have a bad or dirty MAFsensor? Would that cause my engine to run lean? I included a video of the surging. Thanks in advance for any help given.

Video (Click to make bigger)

1 Reply

KEN L

MASTER CERTIFIED MECHANIC
47,690 POSTS

Thanks for the video. The P0171 code means that the fuel system is running lean. I would check for vacuum leak first with the engine cold, if no leak is present, I would replace the MAF sensor because cleaning it will not help once the sensor is affected as it is. Here are two guides to help fix the car with instructions in the diagrams below to help show you on your car.

Test with engine cold only.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

and

https://www.2carpros.com/articles/how-to-replace-a-mass-air-flow-sensor-maf

Clear the codes once the repair is complete. Check out the images (below). Please let us know what you find. We are interested to see what it is.

Images (Click to make bigger)