Mechanics

ENGINE HESITATES AND DIES

1998 Mazda Millenia

Engine Performance problem
1998 Mazda Millenia 6 cyl Two Wheel Drive Automatic 165000 miles

I have replaced the plugs, wires, cap, rotor, air, fuel filter and crankshaft position sensor but my car still cuts out at idle and stumbles or dies when the throttle is depressed. Once above idle the engine appears to run OK. The engine does not smoke or use oil, and has had no other problems running since new. I don't see the engine having this problem when it is cold.
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Luvalotus
January 13, 2010.



Is the check engine light on? Do you have a digital multi meter if needed?

Racefan966
Jan 13, 2010.
No codes thrown, and yes I have a digital multimeter and the skill to use it. I appreciate any help guys.

Tiny
Luvalotus
Jan 13, 2010.
Ok if you would first get some mass air flow cleaner. Remove the mass air flow meter and clean it. Then put it back in and see if it runs better. If there is now change then turn it off and unplug the mass air flow meter and start it again. Now does it stay idling? Get back to me with what you find here.

Racefan966
Jan 14, 2010.
I cleaned the MAF, but still have the problem. I checked fuel pressure, it idles at about 32psi and increases when I open the throttle and the pressure was good when I experienced the problem, checked the throttle position sensor and it changes value smooth and evenly. It feels like an intermittent miss at idle, but will get worse to the point it may die if you let it idle for several minutes and will choke like it is starving for fuel when the throttle is opened. It does not do this every time I open the throttle. It also does not seem to have the problem when cold, but the idle is higher then too. I still have no engine codes. I can't find any vacuum leaks either. Thanks for any advice guys.

Tiny
Luvalotus
Jan 18, 2010.
Ok good so far. Now did you unplug the MAF when it acts up to see it is stops? If not please do that. What brand of spark plugs did you use? Did you have this problem before you did the tune up or did it start after the tune up?

Racefan966
Jan 18, 2010.
I have tested the MAF it does make it worse when I unplug it, I have checked every vacuum line, tested the coil primary and secondary and both are within tolerance ( the seconday is just inside the upper limit), checked that every injector is cycling at a steady rate, engine is worse in that it will not idle after it has been running for 5 minutes or more. It will start missing and die. It is harder to start after that like the fuel is not getting to the cylinders but I have good fuel pressure at the rail (32psi at idle). I have pulled the plug wires one at a time and they make it worse each time so it's not a single cylinder. If I cut the A/C on it will idle higher, but will still miss and die even then. The only thing I havent mentioned is that the fuel pressure seems to leak down slowly after the engine is shut off (it takes seceral minutes to drain to around 15psi). I have done every thing I can think of, so I hope someone has an idea as to what it might be. I have removed the throttle body to clean the BAC and IAC valves and will be reinstalling tomorrow.

Tiny
Luvalotus
Jan 18, 2010.
I forgot to add that the plugs are Bosch Platinum and I have used them throughout the life of the vehicle. Also I tuned it because it was acting up.

Tiny
Luvalotus
Jan 18, 2010.
Ok thanks. Did you check for any vacuum leaks within the intake and such?

Racefan966
Jan 19, 2010.