Throttle hesitation at 1200 rpms in 5.7L

[Goob]

I have a throttle hesitation that recently developed in my 5.7L with 117,000 miles on it. At 1200 rpms driving 50 mph down the road in overdrive the engine will surge between 1200 adn 1500 rpms. This will stop once the engine warms up to normal operating temp, or if I down shift to 3rd which raises the rpms. Trany fluid is ok, I changed plugs, cap, rotor, and fuel filter at 100,000 miles. It had a new intake gasket at 90,000. Can it be an intake leak? I have a small oil leak comming off the block just above the power steering pump? Fuel pump? Injectors? The computer hasn't thrown a trouble code yet. Anyplace to start?

 

Thanks

[GM-Tech]

This sounds like a surge, not a hesitation. A hesitation typically occurs when pulling away from a dead stop. As you press the throttle, you hit a dead spot and the vehicle, well, hesitates or holds back slightly. Then, after that momentary hesitation, it accelerates normally. This was something that happened on carbureted vehicles when the accelertor pump was bad. Rare on an injected vehicle.

 

A surge is a more gradual increase/decrease in engine rpms with a steady throttle position. A buck, or fishbite, feels just like... if you've ever been fishing, it's the feel when a fish tastes, lets go, tastes, lets go. You get that slight tug feel. A surge is smoother.

 

So, would you say it's more of a surge or a fishbite?

[Goob]

This sounds like a surge, not a hesitation.  A hesitation typically occurs when pulling away from a dead stop.  As you press the throttle, you hit a dead spot and the vehicle, well, hesitates or holds back slightly.  Then, after that momentary hesitation, it accelerates normally.  This was something that happened on carbureted vehicles when the accelertor pump was bad.  Rare on an injected vehicle.

 

A surge is a more gradual increase/decrease in engine rpms with a steady throttle position.  A buck, or fishbite, feels just like... if you've ever been fishing, it's the feel when a fish tastes, lets go, tastes, lets go. You get that slight tug feel.  A surge is smoother.

 

So, would you say it's more of a surge or a fishbite?

 

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It's more of a surge, no dead spots.

[Goob]

It is a surge, no dead spots. It feels more like the tranny than a misfire.

[GM-Tech]

While driving down the road when this is occuring, lightly step on the brake pedal. You want to push it just enough to cause the torque converter clutch to disengage, but not enough to apply the brakes to any degree that will slow you down. It shouldn't take more than a light touch on the brake pedal.

 

Hold the pedal in that position and see if this makes the surge go away.

[Goob]

Yes, slightly depressing the brake pedal makes it go away.

[GM-Tech]

Yes, slightly depressing the brake pedal makes it go away.

 

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That's the torque converter clutch, so you either have a trans problem or a control problem.

[Goob]

Yes, slightly depressing the brake pedal makes it go away.

 

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That's the torque converter clutch, so you either have a trans problem or a control problem.

 

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What does control problem mean? Thanks for all the information. Sounds like it is a little over my head, not just a nuts and bolts tranny swap. I'll have a transmission shop take a look at it.

[GM-Tech]

The torque conv. clutch is turned on/off electrically, so there are a lot of components involved that control it.

 

Maybe I should clarify. The TCC itself is applied hydraulically, but the hydraulics are controlled electrically. It could be a hydraulic problem or an electrical problem.

[1998Z71]

What exactly would the needed repairs be for this problem? I have exactly the same problem on my 98 Z71. It started to do this probably more than two years ago, no real problems, just really annoying. I have 146,000 on the truck now, it started at roughly 120,000.