Q: Car is running slow, what could it be?

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The codes I’ve been given are P0502 & P1406. My check engine light is on & my speedometer isn’t working; it’ll get up to what feels like 30 mph & sometimes do a jerking motion/speed up or start to slow down. I've also noticed that on the right side a fan will start up & my car makes struggling noises. I’ve been told to check my Transmission Fluid, but that looks like the proper color & fills to both holes on the dip stick. I’ve had a mechanic come out once for checking the problem & again to fix a possible solution (speed sensor). After the 2nd time, he told me I would need a speed sensor pigtail connector, which I found & need replaced. Any suggestions if that might not work?
My car has an automatic transmission.

If you already replaced the sensor then now it will need that connector you’ve mentioned. Replacing it may fix the code P0502. The code P1406 is for the EGR valve position, you would need to have the valve tested to see if it is stuck open or if the valve is bad. Have a pinpoint test done on the code P1406. I suggest to have a qualified technician perform these checks and properly diagnose your trouble codes further. From there they can perform the necessary repairs. Good luck

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