I have a 04 mazda 3 I 2.3L auto. With the car in drive with the brake applied the idle drops to around 450 rpm. If I release the brake but remaining in drive the idle returns to normal 700 rpm. In park or nuteral with brake applied the idle is normal. the idle only drops if the trans is in Drive and the brake is applied.
If I remove the Horn fuse , the idle is normal , 700 rpm in all gear positions and brake positions.

Anyone had or herd of this problem.

ktm181

 

check the passenger junction box (behind the glove box), it controls a lot of the electronics, and since the horn shouldn't have any connection with the brake or idle, i'm guessing a corrosion issue is the problem.
How'd you find out the horn fuse removel fixes the issue anyway? seems like an odd thing to check.

 

I will take a look at that Junction box. I read somewhere that the horn fuse also controls the brake circuit.
And it does, when I remove the horn fuse the brake lights no longer work, and the gear shift lever is locked in park. To perform the fuse test I have to put the trans in N , then remove the fuse. Thanks again for the sugestion I will look at that J-Box

ktm181

 

There are two horn fuses, F38 in the PJB is the 12V side of the relay for the horn, as well as the source for your brake lights... which you need so people don't run into you!!!
you can try pulling the horn relay instead to see if that has the same effect.

 

low rpm, rough/unstable idle on brake apply may be caused by leaking vacuum brake booster diaphragm or atmospheric valve (faulty vacuum booster ).

Scott

Do you hear a hissing noise under the dash on brake apply?

 

Hi, I have same problem but if turn on front lights RPM are ok, I have a 2.0 litres automatic trasmision, any solution?
thanks

 

I have the same problem. Have you been able to sort it out ?

 

Hi mate. I have the same problem with a Mazda 3 I'm working on. It's been a few years since your car had a problem. Did you get it fixed and what was the cause ?

 

check/replace the 02 sensor 1st

 

did you fix the problem?? please can you tell what it was,,, I have waste several money already,, thank you!

 

Hi ktm181,
I have the same problem with my 2006 Mazda 3 2.0L auto. The idle drops off to about 5oo rpm when the transmission is shifted to "D" and the foot brake is applied.
I also have removed the stop/horn fuse and all is then OK. I would really appreciate any information regarding fixing this problem as I have tried the following to no success.
Cleaned throttle body and MAF sensor, check purge valve, checked for air leaks, run a diagnostic test no codes.
Regards
SSB

 

Hi mazda32005, I have the same problem, can you give any advise?

 

Hi Mattrac, I have the same problem on my 2006 Mazda 3, can you give any advise?

 

HI tomasv, I have the same issue with my Mazda 3 2006, can you give any advise?

 

For my 2006 Mazda3 2.0 auto also faced the same problem recently, i.e. low idle (500 rpm) when brake applied when in D gear. Spent a bit monies to check but in vain, Is there any fix for this problem and what is the real cause of the problem? Many thank!