Mystery fire air filter and housing

I took my 1998 Infiniti I30 to my mechanic for routine maintenance, and I noticed the engine was working a tiny bit harder to startup and to accelerate on highway in the last 2 weeks. They discovered the air filter and housing were completely burnt out! We’re scratching our heads. Internet search and check with other mechanics- no clues. It’s been a dream for years with routine maintenance, has only 125k, last service May 2013 since I only drove it 5K since then. I’m the only driver and it sleeps in my garage (secure, no rodents). What the heck? Thank you for any answers.

Your two options would be an electrical short - but I don’t think this box has any wiring that goes into it - or backfiring through the intake. Since I don’t think any electrical stuff is involved I’d have to guess that over the past couple of weeks’ loss of power you’ve been having a pretty big issue that is causing backfiring. Is the check engine light on? Your shop has to look for the cause of persistent backfiring - things like timing chain problem, preignition, valve problems, clogged exhaust…

If you look at the housing you can see where the hot spot was. Where the big melted hole is.

Before installing the replacement filter box, I would check to see what could get so hot in that area to melt a hole that big.

Edit: What did the Mass Air Flow sensor look like?


My guess is some debris was set on fire by the MAF sensor wire.

The filter is totally gone! I think you must have had a backfire that spit raw, burning gas into the filter. But my next question would be, how far is the filter housing from the engine intake? Is there another plastic tube that connects the filter housing to the intake? It’s surprising that the connecting tube would be in good shape, but maybe the air filter housing was the only place that had enough air available to support combustion. Maybe the air intake picked up some dry leaves or something else that helped the fire get going too.

Someone left a rag in the airbox and the MAF set it on fire?

I’m guessing an engine backfire into the air filter. Sometime this can happen just by completely running out of gas. Has that happened since the last time this area was inspected?

I looked at those pics again, got myself right side up, looked at the I30 intake set up - I don’t think that could have originated in the engine. Not only would that just be odd and rare to begin with, but between the TB and air filter are two small pieces of intake hose, a resonator box, and the MAF.

What does the MAF look like? The intake tube and resonator box? Does the PCV system hit the air box at some point? Here’s another totally half-baked theory - your intake sucked in a lit cigarette butt that was bouncing down the road from a vehicle in front of you. That’s slightly less half-baked if there is a PCV connection that brings any oil vapor or residue into the box.

Thank you all for the ideas. I got similar from Brad Bergholdt ‘Under the Hood’ columnist in Pacifica Tribune/San Jose Mercury News Group. I reviewed these with my mechanic who confirmed the MAF, check engine light checked out fine. He pointed out the nearby intake, and that there were some leaves in the burned out box. I never noticed engine backfire.

My mechanic and I did a visual since repair - all looks good. The car drives like a dream again after routine service also done. I got lazy and stopped doing all the little checks my dad taught me- check fluids, do visuals on engine and tires- time to resume this. Best assumption- leaves sucked in through the intake then ignited? Thanks again.

I don’t see leaves just spontaneously igniting in an air filter box. It’s not that hot in there - if leaves caught fire in a filter box, trees would spontaneously combust and be torches in the fall.

I’m wondering if maybe the hood prop rod or some other hunk of metal got jammed over the airbox. Looking at the picture, if a piece of metal got jammed it could possibly touch the positive battery terminal and the shock tower and cause an electrical arc, but that’s just a wild stab in the dark, because there’s really nothing over there that should set it on fire.

I would recommend very carefully and with a flash light going over every wire in the vicinity to see if there are any signs of arcing or burning. Beyond that, I would consider who my friends are and if any of them are stupid enough to put something flammable in there as a joke.

Pic of a '98 i30 engine bay for everyone’s reference:

You didnt drive through a pile of burning leaves any where did you? The car obviously aspirated something hot or glowing and it ignited some fine residue or chaff in the intake(unless a backfire did it,unlikely)-Kevin

I’m still going with the lit, discarded cigarette butt - perhaps ending up on the leaves and other debris. I’ve heard of this happening and have seen pics of singed and burned air filters (never that much damage to an air box though). And I don’t know where the bottom of the intake box goes on the infiniti but I know that on at least one of my cars this is perfectly possible given the orientation of things. On other cars the set up of the pre-filter intake would make it unlikely for any debris like that to make it to the air filter.