PT Cruiser to live on

My Aunt has had 3 of them. She really likes them but she has had
some really odd ball problems. One of them would refuse to stop
running when she turned the key off. Modern cars have too many things
under computer control just to save $50 in wiring costs. Her first
was non-turbo Touring, the second was a limited with turbo. She
complained that the second on didn't get nearly as good of mileage as
the first. Based on her experience (and others I've heard) I would
not get the turbo because I want halfway decent mileage. Her third
was a basic model because she was out of money and that was all she
could afford. My Dad is on his second Pontiac Vibe (same as Toyota
Matrix) and he has really liked them. If it were not for their
satisfaction with these fairly small yet versatile vehicles I doubt I
would have considered the PT or similar.

 

Sounds like the old "dieseling" effect. I thought that was gone at the end of the '70's when all the engines were
strangled on emission controls.




"What do you mean there's no movie?"

 

Dieseling was. But when the act of turning off the key only "suggests"
to the PCM that it needs to shut the engine off, odd things can happen.

At least the PT isn't throttle-by-wire. I've never heard of anyone
having problems with a TBW car thinking they were flooring it when they
just barely touched the accelerator, and TBW cars tend to have a very
nice "feel" to them (especially since the PCM can throttle back the
engine seamlessly when the transmission is in the act of shifting). But
I still have to wonder what will happen when those potentiometers moved
by the accelerator pedal get old and gritty....

 

No doubt part of the firmware looks for signs of such problems - like
instantaneously jumping voltages (from a dirty or worn potentiometer)
rather than continuous changes that have to occur no matter how rapidly
you move the gas pedal with a 100% working sensor. But I agree - it is
scary to have too much direct control of something like acceleration by
a computer designed by people who *think* they have anticipated every
possible failure mode.

 

Google "Prius big hand syndrome"

 

I'm sure it does look at that, just like firmware has looked at the
output of throttle-position sensors for years and set a code when they
get glitchy... but even still I've had a TPS render a car miserable to
drive before the computer figured out it was dead and started ignoring
it. The problem with fault detection like that is that it changes the
odds of a fault causing something unintended from something like 1 in 2,
to 1 in <very large number>. But it doesn't make the odds *zero*. I
guess if they can get the odds comparable to the odds of a stuck
throttle cable on an old-tech engine, then they're good enough. The
difference is that a stuck throttle cable always happens after the
driver has *intended* to apply big power in the first place (though it
always comes as a shock that the power continues after release), whereas
a TBW fault could conceivably apply high power just as the driver
intends to barely touch the pedal.

 

Geeez, I wish I could find those goodies for a C-Body.