Help me start diagnosing my Mazda Protege 2002, please!

Henry.E

Member
:
Mazda protege 2002 FS
Hi everyone,

I have a Mazda Protege 2002 with the 2.0 FS engine. the issue presents in the following way

- When the car is warming up, let's say 10 minutes after turning the engine on, it randomly drops RPMs for less than a second and then it stabilizes.

- It does this for a few more times and then runs fine after the car is fully warmed up

- I noticed that during that time when the car does this, accelerating from a full stop makes the engine stutter a little bit, but only when accelerating from a full stop. Also when the car is fully warmed up, it doesn't do this anymore.

- It only drops RPMs when idling, it never drops rpm when the car is moving.

- the RPM drops more frequently when under load, like when I have headlights on and A/C.

Any Protege experts or techinicians that can help guide me in the right direction to start troubleshooting?
 
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I'd start by doing a visual check of the engine bay. A problem I've encountered a couple of times was a vacuum line (5mm inside diameter) that would split at the connection tube (middle area, closer to the firewall). Hoses and tubing get brittle with age, as they lose plasticizers in the rubber. I just replaced my OEM tubing with 3/16-inch ID x 2 ft (actually, about 21 inches) tubing. If the split gets large enough, a check engine light will illuminate and drivability/fuel mileage will suffer.
 
The alternator could have a hard time keeping up at idle if your battery is weak.

If you have a volt meter you can read the voltage at the battery terminals before you start the car, and then while the engine is running.
 
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