Hesitation Dance

[LauraSVT]

Around town and through the lower gears, I've got great driveability. However, I've got a symptom that appears more in the upper gears that perhaps some of you could sound off on. I have no check engine lights, and no reliablity concerns. No noises -- no signs of any other malfeasance. Plugs and wires are new. Redline fuel injector cleaner has been run.

When the throttle is applied quickly and heavily (this is most notable in fourth and fifth gears), I'm getting a slight hesitation as the car continues to pull. You can hear it -- manifests as a harmonic disruption, an MMMmmmMMMmmm sound, and is accompanied by a few slight jerks. The car does settle in after your foot's been planted for a few counts.

This also happens in the reverse, when the throttle is suddenly lifted. Both scenarios exceed what I would expect just from changes in throttle application. Thoughts?

Many thanks for your help.

 

[TourDeForce]

Around town and through the lower gears, I've got great driveability. However, I've got a symptom that appears more in the upper gears that perhaps some of you could sound off on. I have no check engine lights, and no reliablity concerns. No noises -- no signs of any other malfeasance. Plugs and wires are new. Redline fuel injector cleaner has been run.

When the throttle is applied quickly and heavily (this is most notable in fourth and fifth gears), I'm getting a slight hesitation as the car continues to pull. You can hear it -- manifests as a harmonic disruption, an MMMmmmMMMmmm sound, and is accompanied by a few slight jerks. The car does settle in after your foot's been planted for a few counts.

This also happens in the reverse, when the throttle is suddenly lifted. Both scenarios exceed what I would expect just from changes in throttle application. Thoughts?

Many thanks for your help.

Does it happen only when your AC is on?

Have you checked your TPS?

When was the last time you cleaned your MAF?

How's your fuel mileage lately?

I'm having a similar problem with my Mystique, but I think it's a problem with my IAC valve and/or idle compensation for the AC. My rpms will regularly drop to under 500 at idle, then smooth out at 800ish, then again...

 

[LauraSVT]

Does it happen only when your AC is on?

Have you checked your TPS?

When was the last time you cleaned your MAF?

How's your fuel mileage lately?

I'm having a similar problem with my Mystique, but I think it's a problem with my IAC valve and/or idle compensation for the AC. My rpms will regularly drop to under 500 at idle, then smooth out at 800ish, then again...

The problem is excacerbated by the A/C, but does not go away when it is turned off.

Haven't looked at -- only thought about -- the TPS.

MAF was replaced last year and cleaned recently.

Fuel econ is good -- 24 zipping around with my foot occasionally on the floor in mixed driving.

IAC was replaced 15K ago, and cleaned with Berryman's two weeks ago.

Thanks for dropping a line on this. Feel free to add other insights.

 

[hetfield]

Do you hear anything at idle? What are the plugs and wires you installed?

 

[LauraSVT]

Do you hear anything at idle? What are the plugs and wires you installed?

No noises at idle. Plugs and wires are all Ford Motorcraft, stock specs. Had this issue before changing them, though.

 

[TourDeForce]

IAC was replaced 15K ago, and cleaned with Berryman's two weeks ago.

The IAC might need a little lube to work properly. A quick squirt or few drops of light machine oil might be a good idea.

Check the resistance across the TPS terminals and make sure there is no sudden drop. Transistion from closed to full open throttle should be smooth.

Also, check your accordian tube (seen cracks in them along the fold that is very hard to see), and the attaching vac tubing for cracks and holes. Particularly the hose that runs past the water pump - remove the plastic imrc cover to get a proper look at it. Also carefully inspect the PCV hoses under the throttle body & the PCV valve itself. Pull it & make sure it moves freely - if not, replace it with a new one. They're very cheap and the aftermarket ones are built poorly.

 

[FavoriteMystaque]

What RPMs and gear does your problem happen? I had a surging while moderately accelerating my sister's Mystique at 2200 RPM, 40 MPH, 4th gear if I remember right. Revved up fine, then upshift, hit gas and it would surge. Problem was carbon tracking on Plug 2 center rear of engine. It was a new set of Autolite plugs and wires. Carbon tracking looks like pencil marks or cracks in the ceramic part of the plug. A new plug and thorough cleaning of the boot and silicone grease in the boot fixed it almost 2 years now. Have to use a clean socket to install the plug.

 

[LauraSVT]

With a new throttle position sensor, the car runs perfectly. It is smooth and powerful all the way through the rev range. Also rotated the tires, so ride quality is improved, too. I love driving the car.

 

[FavoriteMystaque]

The TPS gets jumpy, like a volume control knob on a cheap radio. Good fix!

 

[iBrent]

With a new throttle position sensor, the car runs perfectly. It is smooth and powerful all the way through the rev range. Also rotated the tires, so ride quality is improved, too. I love driving the car.

I have a similar problem, except much worse. To be honest, the TPS is probably the ONLY thing i haven't replaced yet. Maybe i'll give that a shot. Thanks for the updates.