Contour Enthusiasts Group Archives Forums General Troubleshooting No power below 3500 RPM - Duratec

My mother's Mystique have a problem since 2 or 3 years for sure. She have a '95 Mystique with the 2.5L ATX and currently have 139 000KM on it.
Well back 3 years, the car always smelled rotted eggs and CEL was on most of the time, in city or on highway, even when drove very gently of very hard. So, we started checking possible causes for that. Since then we checked/replaced them :

- Oxygen sensors (Both changed)
- Plugs and wires (Changed)
- Cat (Checked and OK)
- Intake manifold (Removed and cleaned)
- Injectors (Cleaned by the dealer /w new fuel filter)

The car is serviced every 5 000KM and since a year, we used synthetic oil and premium gas. Premium gas helped a lot and the intake manifold cleaning removed the CEL for good and the rotted eggs odor.

Now, the car have about 80% of his original power, but only when secondaries opens (over 3500 RPM), we can feel we're pushed back in the seat at soon as they open and speed goes up.
But before 3500RPM, it doesn't have any power. I mean, I know that it's running only on 12 valves, but the car doesn't want to accelerate at all if we don't push the accelerator past half. We can feel it struggle, but not that much.

I understand that '95 Duratec are vaccum controled, can it be a broken vaccum line causing this trouble ? If the problem was present all the time, it would be easier to diagnostic, but since it's only when secondaries are closed, I don't think it would be related to fuel or ignition.

Thanks for your help !

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Well, this FAQ entry treat more about problem over 4000RPM than before 3500RPM, but I'll check out the PCV valve anyway.

Secondaries open just fine, it just seems to run lean on gas or air on 12 valves. When secondaries kicks on, she runs fine.

The rotton egg smell though.. that's supposed to be your cats. You say you've checked the cat.. what about the pre-cats?

I'll check for the secondaries, it could be very possible that they stay open all the time...

Originally posted by SpliceVW:

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The rotton egg smell though.. that's supposed to be your cats. You say you've checked the cat.. what about the pre-cats?

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The smell is now gone, as strange as it looks, it was the intake manifold that have been clogged with carbon deposits. They cleaned it and the smell and the CEL are now thing of the past .
The car is driven mostly in town, and that's what probably caused that much deposits in the engine.

I've drive the car yesterday and I noticed that when the engine is started, it rev up to 1500-2000RPM for a minute before get back to 750RPM. I don't use that car very much, but some years before, it would not rev that much.
Also, it run a little rough at idle, and nearly stall when put in reverse, then rev to 1500RPM after when I put it back to neutral, like the engine need to adjust the idle a lot to keep it running in reverse.

BTW, thanks a lot for your help, I'm a newbie in cars mechanic but I like to learn a lot .