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Feeling a "bump" in the gas pedal after coasting...?

1999 Cadillac Seville STS, 130k miles, 4.6L Northstar V8, FWD.

When coasting at around 35,40 mph (and other speeds but most noticeable at those speeds), if I get back on the gas (not hard, just normally), I feel a “bump” in the gas pedal before it accelerates…almost like there is a disconnect in the drivetrain.

If I reeeally ease into the gas, this doesn’t happen. And if I don’t let the RPM’s get down to around 1500, this doesn’t happen (i.e. if I only coast for a few seconds and don’t let the engine get down to “coasting” RPM’s, I don’t feel the bump). It doesn’t happen starting from a stop. There’s no loud thunk or other noise, just a bump that’s mostly just felt not heard.

Took it to the mechanic and they thought it was the front motor mount, which was replaced. Can’t tell if it got any better, it might be a little bit better now, but the bump is still definitely there.

Any ideas would be greatly appreciated before I spend more money on this issue. My main concern is wear on the engine (if it is not mounted securely), or other drivetrain components.


Did this just recently start or did it always do it and you maybe never noticed it until now.
It is possible that this is the electronic fuel injection transitioning from DFCO (deceleration fuel cut off) to normal running mode.

It’s done it as long as I’ve owned the car, which isn’t long. What would make the fuel injection system do that, and is there a way to “fix” it?

Did they check all the motor mounts?

I would think so…but maybe not closely after they found the first one? Do you think it’s another mount? I understand there are 4 total.

I don’t know about your specific car, but it is not unusual for more than one mount to be damaged. They are all subject to torque and when one goes the other ones have to absorb more stress. Put the car in drive and hold the brake hard and tap the gas (not hard). Have someone look at the engine (hood up-stand to the side). If the engine jumps more than what you would expect, you may have another bad mount.

Ok thanks, that makes sense… I’ll try that out and see what the engine does.

Anyone have any other ideas or anything else to check?