I need help fixing this pulsing im having with my idle its getting really bad. Check my sig for my mods.
When i first start my car my idle goes to 2500rpm then slowly goes down to 1500rpm and stays there for about 3 minutes. Then when the the car is fully warmed up i get a quick, erratic pulsing from 1300rpm to about 1600 rpm and it continues for as long as i have the car on.
I just need you guys to know what ive already tried so that it is not mentioned.
Firstly i have checked and adjusted my TPS to within spec.
I have checked EVERYWHERE for any kind of vac leak and could not find one.
I have removed and cleaned the BAC valve as well as check resistancy, and it also clicks when i apply voltage.
I also checked the throttle cable and it is not at all tight.
I just need to know where to go from this point.
Thanks a lot.

 

I have seen bad BAC valves do that.

If you block off the air input into the bac does it solve the problem?

 

I have the same proble. See my 12/5 "eratic idle" posting. I havent figured it out yet but if I do. I'll let you know.

 

my does that but only when I rev it to like 2k rpm it will rev to like 2.3k and then down to 2k probably related just my idle is 900rpm and constant but if it where to idle at 1.3 or 1.5 k it would do that.

 

I dunno ill have to try that.
But i checked the BAC, what else could be wrong with it if it passes those steps in the FSM?

 

My car does the same thing but only in cold weather and only when its warming up, after that its fine

 

The first S5 BAC I used on my S4 to S5 intake converison had that same problem. What was weird was that unplugging the BAC didn't solve the issue. The BAC checked out fine other than that, just like yours.

When I replaced the BAC with a spare one I had laying around, the problem went away.

The only way I figured it was the BAC was that the problem also went away when I blocked off the input air line for the BAC

 

My car used to surge during warm up at about 1600 rpms. It was fine after a TPS adjustment(an unrequested TPS adjustment, I might add, that took me two hours to fix to get my idle back to normal But hey, my surging's gone now! ) The wierd thing was, I didn't have the TPS adjusted to spec. I ended up playing it by ear(read: guestimating where it used to be to get it normal. I know my TPS is bad/dying, perhaps yours is too?

Steve

 

Well you know when i unplugg the BAC the problem continues on the same. So its like its not even doing anything. Im going to try what you suggest tomorrow. But if i block off that input on the BAC what about the other side, does to be blocked off to? thanks Icemark.

This problem started when winter started. It seems that my car hates cold weather. In the summer i have high idle at startup, but then after driving all day on a hot day it goes right to 750. So it seems that for me the idle is dependant on which season im in

 

My car does the same, it progressed steadily worse until I took it to the mechanic two weeks ago. He replaced the belts, water pump and spark plugs and it doesn't do it as bad. My whole powerband is wack. If I rev to 4k and slowly drop down to idle, there are places where it'll do the surge and just drop 2-300rpm's instead of progressing smoothly down. It's worst spot is around 1500rpm's, It doesn't want to sit still, It'll just go rhh..rhh..rhhh as long as I hold it there. It's more of an annoyance than anything else. Sorry I don't have any insight. But I'm going to be watching this thread.

 

Any other ideas on this 1500rpm pulsing a lot of seem to have problems with??

 

I would check the fast idle system.

if it pans out ok, then I would try to set the idle as mentioned in FSM.

if you can't set it, meaning the base idle speed is too high, then you may have some kind of vacuum leak (maybe internal, like acv diaphragm busted or egr)

the bac could be stuck open also (unlikely but it could happen).

Hugues -

 

Here's the deal:
After initial warm up the AWS closes.
After that when the ECU sees the TPS at 1v (closed throttle) it limits revs to 1500.
If anything (EG: idle stop, fast idle cam, BAC bleed, or vac leak) pushes the idle above 1500, the ECU drops the BAC closed until revs fall below 1500.

I think that's where Mazda got the Zoom Zoom advertising thing.

My fast idle cam needs adjustment, so I get a minute of zoom zoom starting about 30 seconds after cold engine start.

 

Ok Icemark i tried what you said and it did exactly the same thing that your car did. When i blocked off the lower air port on the BAC with my finger the pulsing went away and the idle maintained at about 1400rpm but with no pulsing.
So now what does that mean? I must replace my BAC?
Hopefully it gets the idle down too.

 

My car was doing this. I just recently got it under control. I'm contributing mine to either a vaccuum leak or the TPS out of adjustment. Hell, maybe both!

 

bump

 

Your BAC is probably OK.
Something is feeding too much idle air.
When you ground the initial set plug, the ECU drops the BAC function so you can close down the idle bleed screw or the throttle stop if neccessary.

 

Sureshot i dont understand what you mean by this. Can you explain this in a little more detail?