2007 Maxima SL with 190K had to be towed recently for a drained battery. I felt that the tow was impacting the exhaust. A couple of days later after jumping starting the car it started to make a loud rumbling noise and while driving it keeps hesitates when accelerating at speeds above 20 mph.
A mechanic checked it out and said a broken flexpipe was the reason for loud noise and quoted $600 to replace that part. He said he had to diagnose the misfiring issue for a $85 fee. I ran the OBD scan and it gave 2 codes P0300 (superscript $0010) & P0300 (superscript $0010pd). Not sure what those superscripts mean.

1. First, Is $600 a reasonable charge for flexpipe replacement. I'm trying to place a claim with towing company. Otherwise will have to pay out of pocket.
2. Is there a chance that the broken flexpipe be the cause for misfiring or are they unrelated?

Appreciate your help.

 

A few years ago I bought a new flex pipe from ebay for $150. You might want to shop around.

 

Thank you. I was told the pipe is rusted and beyond welding in a new flex pipe. I got the exhaust sectionpipe (part# 642264) replaced for $800 and the noise is gone. But now it threw a 0305 and I'm replacing the spark plugs and the rear ignition coils (even though only coil 5 was the culprit). I'll replace front coils later based on the need. While working on the spark plugs, I found some oil in the 3rd cyclinder. Based on my reading it is a valve cover leak. Is it absolutely necessary to replace the valve cover or can I wait and see for a year or so? This is my first major work on the car and already a bit nervous if everything will work after I put together. I want to avoid valve cover replacement unless necessary adding another failure point into the task of putting it back together.

 

unless you want to replace the coil again replace that VC now

 

Makes sense. Thank you. I saw the video and it seems doable. There is a part where RTV is applied in 2 corners. What is that for and can I screw it up. What would happen if RTV is not properly applied. Would it cause a bigger problem?

 

its so oil doesnt seep past the seams in the head. clean up the old silicone as best you can, degrease oil with brakeclean, use permatex ultra grey silicone. dont need a ton. just a dot where the gasket sits on the seam. generally no more than about 1/4" diameter dot.

 

As stated by slvr2KSE5, It's basically for added insurance as Nissan realized that the valve cover gasket alone couldn't handle the task of prevent leakage.

 

I replaced the spark plugs and 3 coils in the rear. Looks all good now. No codes. Throttle body I noticed is dirty. So, I need to clean it. Hope there is no relearn procedure involved.

 

there is a relearn

 

For full context, I replaced all 6 plugs (NGK) and only 3 (#1, $3, #5) rear coils (NGK) hoping I wouldn't have to deal with the intake manifold atleast for a couple of years.

After a day of driving, I got a new code P0300, random misfire. I thought of doing the throttle body cleaning, but the advise was to do it while the car has no codes. So, I erased the code and drove for 5 miles to see if P0300 will come back again, but it didn't yet. So I went ahead to perform the throttle body cleaning. It was then I realized that each car operates differently. I recently cleaned the throttle body on an Odyssey where the butterfly plate would open with ignition on and have a helper step on the gas pedal. So, what is the process to clean the throttle body. Remove it, move the plate with hand, clean, put it back & relearn? In my mind, I'm not supposed to move the plate manually.
Based on what I'm reading, P0300 is hard to diagnose since it could be plugs, coils, vacuum leak, fuel injectors, timing belt. Any advise on how to move forward. Is it ok to keep on driving if it comes back again if there is no noticeable difference in driving except for the code?