1999 Mazda Protege idle speed changes, occasionally stalls

KARINIER

MEMBER
1999 MAZDA PROTEGE
4 CYL
FWD
MANUAL
90,000 MILES

Protege has new intake manifold gasket on it.
When car is started it runs fine, initially. As it warms up it starts to have idle speed changes of 400 rpm to 1500rpm. When you hit the gas pedal, it runs fine again. Then it begins wandering again, up and down, up down, until it finally stalls out.

3 Replies

MERLIN2021

MECHANIC
17,250 POSTS

Get a can of spray gumout, start the car and spray around, pay attention to vacuum lines and manifold, if the idle changes, you found a leak. You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs!

The other possibilty is the idle air control, it, s bolted to the side of the throttle body.

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Tuesday, August 4th, 2020 AT 12:18 PM

KARINIER

MEMBER
2 POSTS

I think you are right about the IAC and vacuum leaks. I need to get a garage heater first though, to check this out more fully.
Can I clean the IAC, since I priced the part and it costs $350.00. Or is there any way of double checking that this is the cause, other than ruling out the other black rubber hoses leaking vacuum?

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Tuesday, August 4th, 2020 AT 12:18 PM

MERLIN2021

MECHANIC
17,250 POSTS

Ouch! yes I just priced it...WOW, the one on my lincoln doesnt cost that much! I would definatley reove the old one and clean the port out as a trial, but when there gone...there gone. Try finding the vac leak and plugging it. Here's a picture of the little bugger!