Hey guys,

We've had quite a bit of rain here and last week the 7 was sitting for a couple of days in the driveway and when I went to start it, I got a solenoid click but the starter gear didn't spin or engage the flywheel. I figured it was a bad starter and swapped it with a good one.

Same issue.

Got a jump, just in case the battery had somehow gotten low and it started right up and has started like a champ every time since then.

However,

My idle quality and part-throttle cruise is terrible. The idle has a rhythmic blip and the car bucks at part-throttle (just enough to feel it) I tried cleaning the negative battery cable connections and adding a second engine-to-chassis ground, just in case, but it didn't make much difference.

So, in short, the car idled great and only had the faintest hesitation at part throttle before the starting issues. Now, the idle quality is terrible and the part throttle issues are noticeably worse. Cleaning the negative battery cable connection and adding another ground has not changed the situation.

Any thoughts as to what it might be?

Here's a video:

 

Rough Idle and hesitation during acceleration are classic signs of a vacuum leak. But this has more of a pulsation effect, so maybe it is electrical. The Vacuum leak I just fixed in my SE was causing much wilder swings in idle speed.

 

Just a follow up for anyone who's interested:

Turns out that the jump start was just a red herring. I've got the emissions removed and the large nipple on the upper rear passenger side of the intake manifold (anti afterburner valve, I think) had a vacuum cap installed. Unbeknownst to me, the cap split just enough to leak but not enough to be visible/obvious. One new cap later and it's as smooth as buttah.

So thanks to Cameron for reminding me of the obvious truth: when in doubt, check for leaks.

 

Thanks for the follow-up - good for the rest of us dealing with idle inconsistency to first focus on vacuum hoses and caps.