1988 ( Cadillac runaway acceleration)

Is this a rear wheel drive caddy with a v8 engine? Assuming it is
would appear that the CC is the old style vacuum canister with a cable
connected to the throttle body. As far as I can tell it's not drive
by wire so both the gas pedal and the CC use a cable to "give it the
gas". So the first thing you should verify is that your mechanic
actually disconnected and removed the cable that goes from the CC
vacuum canister to the throttle body. Maybe he just unplugged an
electric connector and figured that would be enough. And maybe it is,
but if you disconnect the cable it's a done deal, no ifs ands or
butts. Once that is removed there is simply no way that the CC can
control the throttle even if it was working perfectly and you wanted
to use it. So that's the first thing to check. Once that cable is
gone there really isn't any intended way for the throttle to open by
itself unless you push on the gas pedal. There is a remote
possibility that the throttle return spring has come off or broke
(sometimes there are two of them and maybe only one came off). If
it's missing, for example, one of two return springs there is at least
a possibility that if you push on the pedal that the air rushing thru
the throttle body will open it even further then you intended, maybe
open it all the way. I don't know, just a guess. There also remains
the chance that the new parts your mechanic put on, like the idle air
control valve/gizmo is bad.

Item 22 in this diagram is the cable...
http://www.tonkinonlineparts.com/sho...ey_model=15756

On Sun, 19 Apr 2015 15:29:20 -0700, The Real Bev
> wrote:

>On 04/19/2015 01:30 PM, Ashton Crusher wrote:
>> Bev,
>>
>> My first thought was disconnect the cruise control. I see you listed
>> that it had been disconnected. What specifically was disconnected?
>> Electrical connections? Vacuum connections? A control cable from a
>> "box" to the throttle body?
>
>I don't know. I assume he did it in a way that would completely
>preclude it from causing the problem. It's a 1988, BTW. I stupidly
>forgot to mention that :-(
>
>> My limited experience with idle speed valves/controllers is that they
>> can't "do enough" to really feel like "full throttle" although they
>> could make the engine go perhaps 2000 rpm with no load and when under
>> load make it like you still have your foot on the gas when you are
>> trying to coast down, i.e. it might be able to keep you going 60 mph
>> on a level road.
>
>Nope, this was full throttle pedal-to-the-metal. Seriously hard braking
>to get the car to actually stop such that I don't think my mom could
>have done it. No idea what the RPM was -- you have to push several
>buttons on a hard-to-see console to get to that, and I was kind of busy :-)
>
>> So aside from really weird stuff like a computer gone mad, I'm still
>> thinking something is going on with the cruise control system but that
>> depends on how the one on this car is set up.
>>
>> When the car does this "sudden acceleration" does your foot on the
>> brake make it stop trying to accelerate and it returns to just idle
>> speed or does it fight you to a stop and keep revving till you turn
>> the engine off? If tapping the brakes makes the engine stop "running
>> away" and causes it to return to idle speed it sure sounds like the
>> cruise control has somehow engaged.
>
>Nope, it fights me every step of the way until I can turn the engine
>off. I don't want to do this in a traffic lane on the freeway, so I
>pull over to the shoulder. I've been thinking that perhaps I should
>shift into neutral and shut the engine off, but steering and braking
>without the engine is a nasty business and I don't like to think about
>having to do that in traffic. OTOH, if I can't get over to the shoulder
>that's probably the only option.
>
>I also don't feel comfy restarting an engine until the RPM drop to 0.
>Nasty sounds from the starter gears :-(
>
>> I'm guessing this car is "drive by wire" making the cruise control
>> just a bunch of speed sensors feeding a computer that then tells the
>> throttle how far to open. Disconnecting some of the wires from the
>> buttons in the steering wheel won't fix it if one of the parts of that
>> wire going to the computer is worn thru and shorting out somewhere
>> buried under the dash.
>
>Art is pretty smart -- I would guess that he would have thought of
>something like this. I don't know why the cruise control stopped
>working, it just wouldn't come on the next time I tried it -- after
>maybe a couple of years of never using it. I hate cruise controls and
>was just testing it.
>
>If it were a wiring problem I would guess that it would happen more
>frequently. Last time it happened, BTW, was over a year ago.
>
>> BUT, one of the other issues is that all cruise controls I've had are
>> set up so that they WILL NOT engage under about 25 mph. That would
>> mean it couldn't be the cruise control doing this from a dead stop
>> unless the computer or wiring or sensors was seriously messed up.
>
>The CC in the monsterhome resumes speed in a civilized manner, not a
>full stomp on the accelerator. Given the wussy nature of the Cad, I
>would guess it behaves the same way.
>
>
>> On Sun, 19 Apr 2015 09:29:22 -0700, The Real Bev
>> > wrote:
>>
>>>This (rec.autos.driving) used to be a good group. What happened? On
>>>the off chance that anybody is still actually alive, posted below is
>>>what I've posted into two Cadillac "forums" with no help whatsoever,
>>>although one person suggested replacing the stuff that had already been
>>>replaced.
>>>
>>> At least 5 times (2 with witnesses) this car (which I inherited
>>>from my mom in 2007 with 65K miles on the odometer and which has
>>>sentimental value) has suddenly accelerated as if I had floored the
>>>accelerator. I brake as hard as I can, pull to the side and shut the
>>>engine off. When I start up again everything is normal. The first time
>>>was from a full stop, with two more occurrences within the next 50 miles
>>>at freeway speeds. One time going uphill on a mountain road, and the
>>>remaining times at freeway speeds.
>>>
>>> I've had this stuff replaced by a trusted GM independent mechanic:
>>>
>>> Feb 2011 Replaced the idle speed actuator (idle air control valve
>>>D6576 due to accelerating on its own.
>>> Mar 2012 Replaced the throttle position connector HP4460, Throttle
>>>position snsr/throttle position sensor TH38, throttle spring kit (fast idle)
>>> Oct 2012 Rebuilt smog pump 32-428, serpentine belt. Disconnect
>>>cruise control and inspect powertrain computer for internal failure (tap
>>>test). Replace broken engine mount.
>>>
>>> I never used the cruise control, which stopped working while my mom
>>>still owned the car. It has 85K miles now.
>>>
>>> It's done the runaway thing at least once, possibly twice since
>>>then. No codes.
>>>
>>> The mechanic thinks it may be the computer dropping out and then
>>>resetting itself at full throttle, which sounds even dumber than
>>>deciding that a car should decelerate SLOWLY when you take your foot off
>>>the gas, and that there is no guarantee that a replacement will be any
>>>better.
>>>
>>> More recently it has started to occasionally maintain speed on
>>>level ground when I take my foot off the gas, and may have occasionally
>>>slightly increased speed, but braking stops this instantly. I haven't
>>>talked to the mechanic about this yet.
>>>
>>> I really hate to junk a car with only 85K miles, especially my
>>>mom's car, but even though I'm 5 for 5, it's still scary.