Higher RPM @ Idle with aftermarket muffler

[skip029]

So with my new Nissan I put on the aftermarket muffler I bought a few years ago. If you ebay search "UNIVERSAL DTM DUAL TILT TIP PERFORMANCE EXHAUST MUFFLER" thats the one. I had it on my little green 1997 Saturn SC2 for about 3 years and took it off for the Nissan. I don't remember it being as loud as it was.

I guess I'm just too old now because the deep noise that was cool sounding when I was younger, definitely wasn't doing it for me today lol. Or maybe it was just the fact that I loved how quiet my Nissan drove and it was weird to hear anything other than silence.

Anyways, I put the muffler on and I noticed that at idle my RPM shot up to about 1200-1300 RPM. I didn't like the loud deep noise so I asked the shop to put the stock muffler back on (which looks fine too) and my RPMs went back to being 600ish RPM at idle.

I'm going to take it that the higher RPM at idle was a bad thing due to back pressure? My brother told me that higher RPMs also meant I was going to burn more gas too. So I basically just flushed $150 down toilet to put it on and take it back off

 

[71Chevyguy]

Very possible that the backpressure was the issue, also remember that Nissans do not adapt idle themselves like other cars do. DO NOT attempt to ever clean the throttle body yourself because the idle has to be re-learned by the dealer afterwards. Could be the same type of situation. Had that issue with an altima once and it had to be towed to the dealer to have the idle re-learned since after the throttle body was clean the idle was now 1,700 RPM.

 

[expat]

I'd say the idle went UP because of the reduction in back pressure when the aftermarket muffler was fitted.
I agree with you with the sound. I recently fitted a Flo Pro Baffled, stainless, muffler to my Toyota Truck. It's too loud! I may try and add an additional muffler to reduce the sound.

 

[cmf]

Originally Posted By: expat
I'd say the idle went UP because of the reduction in back pressure when the aftermarket muffler was fitted.


Exactly. Even small changes can affect the idle. I replaced the PCV valve on my car with 65k because I felt like it and my idle went up maybe ~20 rpm at idle. Enough to where I could tell that the RPMs were slightly higher. Resetting the car via disconnecting the battery cable has put me back at what my idle originally was. I normally reset the computer every time I do something but I wasn't expecting the new PCV valve to have any effect. That sucks if yours has to be reset by the dealer though.

 

[skip029]

71chevyguy you were correct!! I finally got a hold of the Nissan service department in my area and they said it was likely due to the ECU registering high air flow and so it cranked the RPMs up

Now I'm [censored]. I wonder why the other shop didn't mention anything before I had them take it off? Nissan service said that they could probably just re-program it for me. I wonder if I would have disconnected the battery and reconnected would've worked too.... [censored].

I guess you live and you learn lol.

 

[mechtech2]

I can't believe the idle is not self adjusting.
Give it more time or re-boot it.
If you got that massive of an idle change, the stock muffler is a huge cork. To note this much at idle is especially concerning. It is hurting , not helping.

 

[Scott_Tucker]

There is no way less backpressure from an aftermarket muffler made the idle jump up 400 rpm. Exhaust systems have the least amount of back pressure at idle so there is no way the stock muffler would have been a restriction. Every new vehicle also has automatic idle control. I don't know what caused it without looking at but I can guarantee it was not the muffler.

 

[mechtech2]

Right.
At idle it would have the least effect.

 

[skip029]

Only thing I changed is the muffler guys, nothing else. When the aftermarket muffler was on, during acceleration it was just too loud for my taste but did become silent at constant speeds or deceleration. RPMs went back to normal after installing the stock muffler. I don't know what else it could be.

I just really wish I would've known about this before I dropped $150 for nothing.

 

[Scott_Tucker]

I know it looks like it is what caused the idle to go up but it is impossible. He must have done something else between these two events like disconnecting the battery or something.

Yes, it sucks that you had to shell out that money for nothing but live and learn.

 

[mechtech2]

Like Scott said, maybe the computer was disconnected for a while to allow welding.
This would cause the idle to be off for a while.