I know I've said it before, but I think I have finally solved the
Herky-Jerky problem I posted about
here over the last several months.
As a final effort to diagnose the problem, while we were on vacation
for a month
I left it with an independent garage noted for their diagnostic
talents. Naturally, they found nothing concrete, just
like my other independent and the Buick dealer. However, they did say
it sure seemed like ignition break-down.
Some of you may recall that I replaced plugs and wires early on in the
ordeal, using the OEM AC plugs but
Federal-Mogul wires from a local parts store. Someone on this listed
said at the time that "new wires
are sometimes worse than the ones removed," and the Buick dealer
complained mildly about "non GM parts
on the car." Finally, in desperation, I decided to follow up on these
thoughts and replace the wires again,
this time using the genuine GM set, which by the way were cheaper than
the Federal-Moguls. As you have
probably already guessed, the problem seems to have gone away. I'm
hedging a bit since there have been times
in the past when I thought it was fixed only to have it come back.
However, over the months I learned it would
always happen if I drove the car about 20 miles, stop for a Starbucks,
and drive back, all in the warmth of a
Southern California afternoon. I've now done that twice since putting
the GM wires on, and got absolutely
no herky-jerky, so my confidence level is higher this time.
Just to review, here are the other things done, none of which fixed
Coolant temperature sensor
Throttle position sensor
Did not replace it, but ran with the EGR valve disconnected
Fuel pressure sensor
Tested rail pressure
Gasoline additive to displace water
Spark plugs (twice)
Spark plug wires (non-GM)
In the meantime, we bought a new Avalon. So, the Park Ave is up for
sale and I will probably never know
if the GM wires really fixed it in the longer term.