Popping/backfiring sound when idling

Post by **gnalan** » 22 Aug 2020, 13:55

I can hear a popping/backfiring sound, and feel it through the air box with my hand on it. Has anyone else had this problem, or know what would be causing it?

There's no codes checking with DiCE/VIDA, so I don't know where to even start to find what/where the problem is.

It also doesn't matter if the MAF sensor is plugged in or unplugged it still stumbles, hesitates, and hunts around trying to idle both ways. I've tested the ETM with VIDA, and it seems to be ok. I was thinking a vacuum leak somewhere could be causing the rough idle, but I don't think that would cause a popping/backfiring sound all the way up into the air box would it?

This is the NA B5244S, so no turbo to cause any additional problems.

ignatz · Post by **ignatz** » 22 Aug 2020, 17:00

Check compression. Maybe you have a bad valve leaking back.

Post by **gnalan** » 22 Aug 2020, 17:11

I was hoping to hear more of an easy fix, but it doesn't sound like it's going to be. I'll rent a guage tomorrow and check it since they're closed now.

This car has been nothing but a nightmare since I bought it, and was probably a nightmare for the seller and the reason for getting rid of it.

There's a 2001 S60T for parts about 3 hours from me, for $400. Any chance the parts for the engine will interchange with the NA engine if I do have a bad valve, or worse?

Post by **cn90** » 24 Aug 2020, 17:23

Is 2001 model year affected by the infamous Throttle Body issue?

How many miles in your car?

Post by **gnalan** » 24 Aug 2020, 18:06

Right now it has 182,068 miles on it.

Post by **cn90** » 24 Aug 2020, 18:43

Search forum, I am not familiar with 2001 but it might be ETM, Xemodex issue.

Post by **gnalan** » 24 Aug 2020, 19:05

I checked the ETM with VIDA, both cold and at operating temp after the idle started hunting around. Everything checked out ok, at least from what I could see. Both cold and hot the variation was under 7, which I think 13 is the factory limit.

I have seen a difference in VIDA between the desired throttle position and the actual throttle position. Desired value stays at a fixed number, while the actual value is all over the place. Could this be my idle problem, and what's causing what sounds like backfiring through the intake? What would cause the two values to be different, and the actual value to jump around like it is? I'm hoping it's an easy fix, possibly a TPS problem, rather than a bad intake valve/spring or worse. Maybe a wiring issue somewhere? Would that cause my problems?

Post by **cn90** » 24 Aug 2020, 19:24

I'd check the fuel quality first.
This happened right after you filled gas at that Sunoco gas station.

Post by **gnalan** » 24 Aug 2020, 19:26

I've already filled it twice at Kroger's since then, and I'm still having the same problems.

Georgeandkira · Post by **Georgeandkira** » 25 Aug 2020, 14:27

Time WAS that "backfiring through the carb" was associated with lean conditions.
I don't know if today's hardware and software allow such a thing to occur.

Be easy whilst removing the spark plugs. I've taken to cracking them free and adding a fews drops of oil down the well and "back 'n forthing" the plug to get the threads lubed...steel plug body in aluminum head and all.

That "desired value vs. actual value" ETM measurement may be speaking volumes. The absence of solid positioning data is what the MM ETM problem is all about. The oxide coating on a piece of mylar plastic wears off and the resulting positioning signal jumps around. This causes the hunting.

Also, if a bad load of gas can be mentioned then so can a clogged fuel filter. It is the most neglected, you know!

Man, 182K is well beyond the point where those early ETM's went bad.
You're eons and light years past the warranty extension so, if you stumble upon notice of such a warranty, ignore it.
Also, a different colored label was used to differentiate an original ETM from a replacement.
White and yellow were the colors but I do not remember which was for what.
Plus it wouldn't matter. If your ETM is bad you need a modern Xemodex rebuild, not a replacement oldie.
They replace the fragile mylar strip with something else.