It's not dying (hasn't yet) but when the car is idling or in low RPMs the car (Mazda Protege 5 2002) is fluctuating in RPMs.

Also, the last start was rough.

I've had issues with air intake before that seemed similar (cracked intake) but this seems a little different. I don't recall the rough idling having the regular up/down like it is doing now.

Any idea what I should be checking first?


This sounds like a problem with the Idle Air Control (IAC) valve. This valve is a small motorized gadget which helps maintain the idle in the engine. (NOTE: Not knowing what year your car is, I looked at the last year for the Protoge5, which was 2003, which does have an IAC.) You may be able to clean up the old one with some carb cleaner, which I would try first. Next, if that doesn't work, I'd try a SeaFoam treatment. If that fails, you would next try to replace the IAC.

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    Problem just went away on it's own. I will try to fix by cleaning the IAC once it comes back (to know whether the problem was fixed, not postponed) – Daniel Jun 15 '15 at 23:39
  • I started seeing ssome stalls now, and I've tried cleaning the IAC, which didn't do much. I did replace the IAC solenoid (with a used one) and found that the rough is not as bad, but still quite rough. – Daniel Jul 2 '15 at 23:38
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    While your at it, clean the throttle body and the MAF sensor, can't hurt. – Capsule Jul 3 '15 at 2:37

Check engine fresh air intake hose, look for cracks in the bellows region in the middle.

  • having had that be a problem in the past, that was the first thing I checked. However my alternator went kaput since and I haven't spent the time and energy to fix it yet, which could have caused these issues, and I've noticed that a cold start often got a bit of white smoke coming out the tail pipe, also could be related. – Daniel Mar 10 '16 at 2:04

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