Mechanics

ROUGH IDLE WHEN ENGINE IS WARM, POOR FUE

1997 Mazda Protege

Engine Performance problem
1997 Mazda Protege 4 cyl Front Wheel Drive Manual 240574 miles

My car still runs great after putting a couple of repairs to it.
But there is one thing; engine starts perfectly fine in the beggining exept I noticed a lower rotations per minute (1000 rpms instead of 1300).
when I drive it and engine is warm, the engine idle decends at 500 quickly when I put my gear on neutral while the car is still rolling.
when I stop at a red light and apply the brakes, engine begins to rotate at lower 500-450 (the car would often rattle and sometimes stall when it rattles too much.
when you let go of the brakes while engine is warm and on neutral " while im parked'', rotations per minute would go up 1000.
I am also experiencing carbon buildup in the engine as well as on the muffler pipe and poor fuel economy.
I changed the spark wires and the car is preforming a little better but still same problem.
I did not open the idle control motor nor I have not spoted any holes in the air hoses.
for the past months I keep losing a little bit of oil in the engines before oil change.
i just want to know wt the problem might be.
real answers, real diagnostics
thank you
Avatar
Joel321
June 21, 2009.



Hi joel321,

Thank you for the donation.

The low idling speed indicates a fault in the idling circuit and the most likely cause is reduced air passage at throttle body or IAC. Cleaning them up and readjusting the idle speed should solve the problem.

As to oil consumption and carbon buildup, with the amount of mileage and age of the engine, valve stem seals should be worn and this would allow oil to get into the cylinders and manifolds. The oil would be burnt or purged out of manifold. Replacing the valve stem seal should reduce the oil consumption by at least 60 %.

Continued use of engine is ok but the plugs would tend to foul up earlier.

KHLow2008
Jun 21, 2009.
I fixed the car myself and discovered that there was a leak in the air vacuum chamber (a crack with air leaking out of it).
When I pathed it up by sealing it with glue, a cut out section of a bag and wire tape.
I also checked the idle control valve and noticed small amounts of gunk in it - really not enough to kill its preformance.
Cleaned it out with paint thinnner.
Spark wires were changed
and drove my car; I noticed better engine torque, no bad idling, better fuel economy
the muffler has no thick smoke; oil is not leacking in valves (same oil level).
Thanks for your help tho it was good to know some of your theories as something to watch out afterwards.
Thanks

Tiny
Joel321
Jun 21, 2009.
Thank you for the input.

I keep thinking of air passage restriction and forgot about the vacumn leakage parts. Sorry if I was not helpful.

Glad that problem has been resolved.

Have a nice day : )

KHLow2008
Jun 22, 2009.