rubles23

What would cause a 2008 Navigator 5.4 to go into limp mode when put in reverse? This doesnt happen evey time, just every once in awhile. At least i think its in limp mode. It will start running real rough and sounds like the motor is coming apart. I believe this happened while in forward also. but mainly just happens when driving then put in reverse to back into a parking space. check engine light never comes up. once you put into park it clears up.

Im not seeing an Idle air control valve on this vehicle. Even looked up one on NAPA website for a replacement part. nothing comes up

I have a 2008 5.4 Lincoln Navigator that Idles around 2000/2100 when in park or neutral. Its has been sitting for almost 3 years with transmission problems. I finally put a used transmission in and seems to be all good except the high idle. It runs and drives fine down the road and when in gear it idles around 800/900. Could the used transmission be causing the high idle issue?? No codes come up. I have checked and found no vacuum leaks. I got the Autel MP808TS scanner and its saying the desired rpm is 2000. What tells the computer to set the desired to 2000? I have seen a few videos about a relearn on the throttle body but not having any luck getting it to change. Any ideas?