[SOLVED]

2000 Maxima 5sp 186k
Just replaced coil packs, plugs, MAF, and IACV
​​​​​
[PROBLEM]

Car seems to run fine when it's warmed up, gets 27mpg on the highway, and idles great. But when I start it first thing in the morning, it:

1. Idols rough
2. Runs rich, I think
3. Has muffled backfires somewhere before the final cat

​I can hear the muffled backfires out of the muffler, but just barely, so the backfires aren't after the main cat.

Any idea why it would be running so rich as to cause backfires when it's cold?

​​​​​​Thanks.

[SOLUTION]

I changed the lower and upper intake manifold gaskets (used RTV one the upper gasket). Fixed the problem.

 

Beginnings of a clogged cat.

 

check the ETCS - Engine Coolant Temperature Sensor

 

Is the air filter clean ? I would start with the simple stuff and work my way down...sounds like it gasping for air

 

Air filter is new. Dirty air filters don't cause backfires and running rich when cold, though.

I'll change the engine coolant temp sensor just in case.

I'll swap my cats from my other car. Dang...I really didn't want to have to do that. It's a pain...but I think that's probably the issue. That's what it sounds like, anyway.

Thanks.