Nissan Repair: 1996 Maxima P0325 & P0400 Nightmare, exhaust leaks, haynes manual

Question
My 96 Maxima has 130k miles.  It runs great.  Aout 3 months ago, I received the P0325 & P0400 codes.  I cleared them and the P0400 came back on a couple days later.  The P0400 seems to come on when the weather is hot.  I replaced the EGR Valve.  The P0400 returned on the first hot day.  I then replaced the EGRC solenoid.  The P0400 returned on the first hot day.  I then replaced the EGRC-BPT, fuel filter and PCV valve.  The P0400 returned on the first hot day after clearing the code.  I replaced all the vacume lines between these components.  I also cleared a carbon clog from the small metal line coming from the EGR valve to the EGRC-BPT.  The P0400 returned on the first hot day.    After I replaced each part I cleared the code with a code reader and the P0400 and sometimes the P0325 would return. Next, I took a small pipe off the engine (right next to the ERG valve and EGRC-BPT) and found a cork of carbon in the pipe.  I have never seen anything like that, but it cleaned up nicely.  This little pipe had a small sensor in it and I also cleaned it.  I cleared the code and it stayed off for a week in 80 degree weather.  I thought I got it.  Then, five days later, both the p0325 and p0400 have returned.  I am tempted to remove my manifold and see where the port is that the tube that was clogged goes into.  I have also read that one of my six ignition coils may be bad.  Lastly, I have heard an exhaust leak can cause such codes to occur.  Any advice would be appreciated.  

Answer
Todd,

Yes, an exhaust leak can cause the codes you listed.  Your model is known for breaking exhaust manifold bolts due the the exhaust manifolds expanding when hot.  I would check for all the bolts first.  Also, the intake track can plug up too.  But, I would check for the manifold bolts and exhaust leaks first since the manifold is a pain to take off.  Do an ohms check on all the coils and any that fall out of range should be replaced.  Purchase a Haynes Manual or go to nissantechinfo.com and view your manual for the $20 buck fee.