Engine stalling on decelleration...

Hi,
Buick Century Limited 89 3.3 300,000 km
Starting cold, drive at about 60kph, let go gas pedal, going for few seconds then stall. Will do this 2 to 4 times for the first 5 to 10 mins then no
more problems.
When it's stalls, I put on Neutral, restart the engine, put back on Drive and go.
Looks like the problem persist only when tranny's cold. The engine will also hesitate sometimes when pushing the gas pedal but only for the very first 1 or 2 seconds, then it goes back ok, but this symptom is omnipresent whatever hot or cold.
Also, on hiway, let's say at 100kph (speed not revelant), as soon as there is no more "pull" (fwd) needed (ie: down a hill or overpass), the tranny shudder like it's "in between" two speed goin up and down very rapidly.
Is there any other thing to check besides changing ATF fluid? A selenoid valve perhasp?
Any clue?
TIA
PS: (Please, spare me the sarcasms, I know it's an old car but I wish to keep it the longer I can since a cant afford another one)
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Fastload wrote:

IMO, the 3.3 is one of the best engines GM/Buick ever made. Do the usual, clean the throttle body, clean the MAP, check the plug wires with them hot, fix all the vacuum leaks, clean the IAC, check the TPS.
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seconds
Drive
also
first 1

whatever
there
TPS.
Did that already. plug need to be replaced soon, will do next month, wires are 6 month old only, TB cleaned 2 weeks ago, MAP cleaned at the same time, Vacuum seems OK since cruise control works great, Scanner tool (Snap on) show all sensor data as OK and within range including TPS and O2, no trouble codes, coil packs checks out OK.
Did I missed something?
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Fastload wrote:

What is fuel rail pressure? How old/condition of IAC? How old/condition of crank sensor? How old/condition of ignition module? Any waveform or p-p voltage on the crank sensor at different temps?
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Lockup torque converter still locked in? Not all the problem, but something...
-- David Algie Algie Composite Aircraft http://members.iquest.net/~aca /
http://groups.yahoo.com/group/algiecompositeaircraft /

no
will
tranny
rapidly.
selenoid
time,
trouble
What is fuel rail pressure? How old/condition of IAC? How old/condition of crank sensor? How old/condition of ignition module? Any waveform or p-p voltage on the crank sensor at different temps?
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Yeah, that would explain stalling in decellaration, is this a selenoid? A valve? Anything I can check?
TIA
PS: Bear with me as I'm a total newbie.

then
the
wires
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Fastload wrote:

As David Algie said, check the TCC solenoid. Parts of your description fit that and parts don't. It should not stall on decel if the TCC is locked until it reaches 10-15 mph or so. The problem usually manifests itself when the trans is hot. Unplug the TCC at the top of the trans and try it out. You will get a 2nd or 3rd gear temp warning light - don't worry but do get it fixed eventually, if that is the problem.
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A
Will try that tonight and let you know.
Thanks
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selenoid?
After a discussion with a mecanic, the symptoms at hiway speed with low load (ie: slight downhill, low RPM) was looking like the TCC is cycling on and off rapidly, it will do it on 3rd or 4th gear only, anyone as experienced that before?
TIA
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no
will
tranny
rapidly.
selenoid
time,
trouble
What is fuel rail pressure? How old/condition of IAC? How old/condition of crank sensor? How old/condition of ignition module? Any waveform or p-p voltage on the crank sensor at different temps?
Fuel pressure check OK 2 days ago, How do you check crank sensor? If bad, it's not supposed to trigger a trouble code? IAC looks OK but do you have a way to certify that? How do you check condition of ignition module? Will try to monitor crank sensor with scope before the weekend.
All parts are original I beleive but I'm not sure.
Stay tuned
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| > > | > > Buick Century Limited 89 3.3 300,000 km | > > | > > Starting cold, drive at about 60kph, let go gas pedal, going for few | seconds | > > then stall. Will do this 2 to 4 times for the first 5 to 10 mins then no | > > more problems. | > > | > > When it's stalls, I put on Neutral, restart the engine, put back on | Drive | > > and go. | > > | > > Looks like the problem persist only when tranny's cold. The engine will | also | > > hesitate sometimes when pushing the gas pedal but only for the very | first 1 | > > or 2 seconds, then it goes back ok, but this symptom is omnipresent | whatever | > > hot or cold. | > > | > > Also, on hiway, let's say at 100kph (speed not revelant), as soon as | there | > > is no more "pull" (fwd) needed (ie: down a hill or overpass), the tranny | > > shudder like it's "in between" two speed goin up and down very rapidly. | > > | > > Is there any other thing to check besides changing ATF fluid? A selenoid | > > valve perhasp? | > > | > > Any clue? | > | > IMO, the 3.3 is one of the best engines GM/Buick ever made. | > Do the usual, clean the throttle body, clean the MAP, check the plug | > wires with them hot, fix all the vacuum leaks, clean the IAC, check the | TPS. | | Did that already. plug need to be replaced soon, will do next month, wires | are 6 month old only, TB cleaned 2 weeks ago, MAP cleaned at the same time, | Vacuum seems OK since cruise control works great, Scanner tool (Snap on) | show all sensor data as OK and within range including TPS and O2, no trouble | codes, coil packs checks out OK. | | Did I missed something?
Can you detect any odours, vapour or smoke when it stalls. If so check the throttle position sensor. That would account for your transmission's apparent gear selection fault. The TPS also sends data to the Buick's transmission control unit. When the TPS says you got her floored, your secondary fuel is active, your spark curve is shortened but your not giving it any vacuum to go with all that juice so a nasty foul smell should be there.
After that I'd look at the EGR and crankcase ventilator valves. (Bypass and Change for cheap). You might want to test the vacuum and take a long listen around your intake manifold when the engine is good and hot and turned OFF. Listen for any hissing or coolant boiling off inside the manifold. That would be an intake manifold gasket.
That would thankfully be the least likely cause. My bet is TPS or EGR. Good Luck. Let us know.
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Lazimodo (nospam) wrote:

for few

mins then no

back on

engine will

very
omnipresent
soon as

the tranny

rapidly.
selenoid
plug
check the

month, wires

same time,

(Snap on)

no trouble

check the throttle

gear selection

unit. When the TPS

curve is shortened

nasty foul smell should

(Bypass and Change for

around your intake

any hissing or

manifold gasket.

EGR. Good Luck. Let us

Problem of hesitating solved!
The problem was: A coil pack!!
One of the coil pack was flaky and when tested in the past was working. Last saturday, the coil pack had gone bad once for all and engine was running rough. Did the troubleshoot to find one of the coil was bad, replaced and the engine is smooth as it was when purchased.
Didnt had the time to test the shuddering on highway yet, will keep you posted.
Thanks to everyone who answered and tried to help.
L8R
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