2003 H6 shudders when driven easily

[Wallis_93]

Hey everyone, just looking for help with a recent issue. So lately I've been driving my car super easy to see what kind of difference I could get in mpg. I did it for a week and had this issue pop up two or three times. The car basically shudders. That is the best way I can put it. It is three quick jolts that almost feel like a downshift except of course there are three jolts. This happens when the vehicle is doing a constant speed. Once at about 45mph and again around 25mph. RPMs did not change when it happened and it sort of felt like something was seizing up. It only happens when driving the car extremely easy and has never happened to me before this week. 

 

My car does seem to have some other problems at the moment. I have a check engine light on for what I believe is either an oxygen sensor or a spark plug possibly. I had the code read and it said one of the banks were running lean. Reason why I say spark plug is because I did not check the gap and feel that maybe it was an issue. Has anyone ever had this happen? I used some plugs recommended on this forum while doing my valve cover gasket. Anyway, hoping to get some advice and appreciate any help!

[Fairtax4me]

Recommend plugs for that engine should be platinum and shouldn't need to have the gap adjusted.

What plugs did you use?

 

The lean code may be due to a loose vacuum hose or breather/phv hose attached to the air intake tube. Double check everything that was touched or moved when you put the plugs in.

 

Beyond that, depending on mileage, it may possibly need the front O2 sensors replaced.

[1 Lucky Texan]

most car parts stores can read codes - could be more than one stored. An ELM327 BT adapter and an app (Torque) on your smartphone can do the same., maybe more helppful readings.

 

shuddering could also be a 'dead' spot on the TPS - I believe there's an upgraded style available for our cars? might be more noticeable at specific steady-state speeds, but not felt during acceleration.

 

tires all the same size/model/brand? any jerkiness felt during tight maneuvering in parking lots?

 

Edited December 4, 2016 by 1 Lucky Texan

[CNY_Dave]

The trans in the H6 cars is for some reason even clunkier than in the 4 cyl cars, it can get a set of learned parameters that make it work like crap.

 

Try disconnecting the battery to wipe the learning.

[1 Lucky Texan]

^^^ I like that - it works for me by eliminating hard downshifting when passing at highway speeds. I do the disconnect trick before road trips.

[Wallis_93]

The plugs I used were platinum but I will try to find the receipt for the actual plugs to make sure. I will definitely try the battery disconnect trick and see how it does. My engine does seem to vibrate more but I think one of my axles is bad and heard it can cause that. Check engine light is back off for now. I will check all the hoses for correct fitment again. Thanks for the advice everyone!

[Caboobaroo]

Fix the issue with the check engine light first.

 

The first generation EZ30D have known issues with the throttle position sensor and the harness for it as well. Under easy acceleration, it can feel like a stumble real quick before it gets out of the trouble area. My car used to hesitate right about 2600 RPM in any gear. I installed new front and rear oxygen sensors, new intake air temp sensor, new spark plugs, and a few other things. Once I could graph the TPS voltage line, it showed me the issue. Since I replaced both the TPS and harness, I've had no issues since.