Nissan Repair: Lean running, intake manifold gasket, nissan altima

Question
QUESTION: Good Morning Calvin, Need some help with a 97 Nissan Altima. Car had engine light issue and rough idle with misfire on cylinder 4. Mechanic replaced plug, wire and distributor cap. Unable to clear code. I replaced fuel injector , removed and cleaned EGR valve. Reset light. Light reappears with " lean running on bank 1 " and rough idle with splashy exhaust. Same as before.  Internet sites suggest that a common issue with Nissan ( ? ) is a leaking intake manifold gasket.  Before I consider doing this , and it appears to be a substantial job , are there any other possible issues I could/should address ?  Would this be your conclusion ?  Hope you had a great vacation !  Thanks

ANSWER: Hi Mark -

Thanks for the well wishes. My vacation was great.

I need some info from you if you will -

Can you tell me what the color of the electrodes are for each spark plug, particularly the difference (if any) between the left bank and right bank (bank #1 is the passenger side)? Is it white, brown, dark brown, or black?

Is the engine running rough?

In my opinion, if it was the manifold gasket, it would be impacting both banks, not just one.

Let me know -
aloha
calvin

---------- FOLLOW-UP ----------

QUESTION: Calvin, All plugs are a light gray in color.  Normal running i.e. road speed is as it should be, no obvious missing , o.k. acceleration etc.  Idle is the rough spot and when the idiot light is triggered. Mark

ANSWER: Hi Mark -

Have you checked the O2 sensor(s). Could be it is not readin correctly and sending a lean signal to the CPU. That would definitely cause a rough idle.

Also check the fuel pressure and volume including the fuel regulator.

If you want to check the manifold gasket for leakage, I believe certain repair shops can do a pressure test for you.

Hope this helps -
aloha
calvin

---------- FOLLOW-UP ----------

QUESTION: Calvin,  I really appreciate your time and effort.  I performed a "test " by taking a handheld propane unit, unlit of course, and flooded the back side and underneath of the injectors and intake manifold with gas. Had two assistants stand behind the car and listen to the exhaust note. When the gas was turned on the idle smoothed out. Take the gas away and the idle and exhaust note went south. I am afraid that that this confirms that the intake manifold has a leak...  Looks like a have at least a day of tear down and R&R of the gasket...   Thanks, again, for all you insight and assistance and wish me luck. Mark

Answer
Hi Mark -

If you can confirm this is not caused by a defective or leaking vacuum device or hose, such as the EGR, restrictors, thermal switchs, etc, then you are correct, I am afraid you have an intake manifold removal in your future.

Good work, and good luck.

aloha
calvin