For almost 6 weeks now I've been dealing with an issue that has kept my car off the road and I'm at a breaking point so any help would be appreciated.

What is happening. When stopped with the car in drive or reverse the idle is dropping down from 700rpms to 550rpms. This noticeably shakes the car and dims the interior lights and happens infrequently from every 30 seconds to a minute or two. The car is running really rough overall at idle but like I said only doing dropping down in rpms in drive or reserve when stopped.

What has been was replaced already. Coil pack, spark plugs, valve cover, seals, both camshaft positioning sensors, crankshaft positioning sensor, cleaned throttle body, performed idle relearn procedure.

A coil pack was bad, oil was present on a spark plug and valve seals were cracked. The sensors were replaced one at a time, testing the car each time, believing this would fix the issue.

What it isn't doing. Throwing any codes; So far no service engine soon light and no codes what so ever. Shifting poorly under any circumstances; It still shifts as smoothly as the day I bought it. Acceleration hasn't fallen off at all either.

What I've read it could be and need your suggestions on:
-Throttle positioning sensor might need to be adjusted
-Air volume learning procedure
-EGR valve
-Timing chain
-Vacuum leak
-Power streering sensor, least likely from what I read

The car only has 89k miles on it and has never had any issues at all. I mean nothing has gone wrong with it in the 5 years I've owned it but this has been dragging on for as long that it is beginning to bother me.

My final question is should I resort to bringing the car to a Nissan mechanic? Is there anything you think they would be able to find out that the mechanic I've had work on my car can't? He's a really good guy who has always done right by me and doesn't want to replace anything else and cost me more money unless we can figure out exactly what is causing this. He has never had an issue like this come up before and that is what has brought me to post here. Thanks guys.

 

Instead of spending more parts and guessing you should go to the Nissan dealership and let them do real time monitoring and tests with that consult II device.

 

i'm a little surprised you didn't suggest buying two more maximas and swapping parts until he had one that worked correctly

 

That's another idea