Surging at slower speeds

[rhubarb9999]

In the past few days I have noticed my 2010 4.6 has a surging issue when cruising at lower speeds.

On my drive to work I have long stretches where I am at a constant 45-50 MPH.

If I hold the pedal perfectly still, the car will (intermittently) lose power. Tach drops a few hundred RPM and the car starts to slow down. Most of the time, after a few seconds it starts to pick up again. But this morning, the speed dropped a full 10 MPH before I pushed down on the gas and got it to pick back up again. There is at least a 1-2 delay between pushing the pedal and getting any acceleration.

This happens to various degrees during my whole drive. Sometimes it will not pull back at all, sometimes only for a second or two. It does not seem to be related to gear changes.

It feels as if the cruise is on and the car is trying to adjust speed. However, the cruise is not on .. it actually only works intermittently as well.

I have also noticed that when I am coasting to a stop, as the transmission downshifts to 2nd gear, it really pulls the car back .. as if I was manually downshifting. Seems a little rough for auto mode.

I have not checked to see what TSBs have been done on the car. Does some of this sound like the 'harsh shifting' issue?

 

[landtuna]

I can't tell you what the trouble might be but I would get the car into a competent shop quickly. You could become a traffic hazard should that deceleration suddenly cause a total loss of power. I had that happen years ago in another car I owned (not a Hyundai) just as I was entering an intersection. Fortunately, I had enough speed to coast through without being t-boned. Scary. Very scary!

You might try pulling the fuse that controls the cruise control and see if the condition changes. Just to ensure the cruise isn't kicking in and out due to some flaw.

The problem in that other car turned out to be a plugged fuel pump. There was a rubber-type sealer in the tank that had deteriorated and little tiny pieces of "rubber" had plugged up a tiny little screen in the inlet of the fuel pump. It was just enough to starve the engine at certain engine speeds but it drove normally otherwise. In cold weather there was no problem but as the weather heated up (ambient air temps 80+) it would occur more often. Adding to the problem.....the car's tech manual did not show the screen and it wasn't until the dealer replaced the fuel pump two times that one of the mechanics found it. I put a standard fuel filter in line with the pump after that and had no more problems.

As for the harsh shifting.....I have a '12 R-spec but I think the same transmission as yours. Normally I cannot feel the downshifts when approaching a stop...until it reaches 2nd. I would not call that downshift harsh but it is definitely noticeable and the car does slow faster than in the higher gears. It has done that since brand new so I never worried about it.