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Discussion Starter #1
i've hit a dead end here...


The problem: hesitation/bucking/stumble. most severely noticeable when at highway speeds in OD with converter locked. if i give it a bit of gas it will run fine. so it's part throttle problem (as if there's a dead spot with TPS).
you can feel the miss at idle with car in park r in gear.


Now:


i did the "let's throw parts at it until it's fixed" thing however:


plugs and wires changed = no change
opti and coil and water pump) replaced= no change
EGR replaced = no change
TPS replaced = no change
Fuel pump, filter and pressure regulator replaced= no change
cats and O2 sensors replaced = no change




so i started taking parts out of the equation to pin point the issue.


disconnected the MAF to see if it'll run fine = no change
disconnected the coolant temp sensor to force it into open loop = no change
disconnected and capped the EGR = no change
took the vacuum line off of the pressure regulator to force max pressure at all times = no change


Data logged the car and i see nothing that jumps out at me.


I'm at a dead end here. only things i have not changed are ICM, IAC, MAP, IAT


possibilities:



bad or plugged injectors?
bad torque converter?




I have done everything i can think of to fix or pin point the issue with no success. i'll attach the datalog to this post


Car is stock other than basic tune and cold air that i did 12 years ago and was running fine until a year or so ago.


i sold the car and bought it back, the guy who bought it basically parked it for 7 years. bought it back and ran fine until this problem started creeping up and got worse.


it runs strong at WOT, even at half throttle, but off idle and a bit higher throttle , this problem is there




Link to datalog:


https://www.dropbox.com/s/65wxcyz8dvyh36y/fleetwood%201-21-19.uni?dl=1
 

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"....problem started creeping up and got worse. it runs strong at WOT, even at half throttle, but off idle and a bit higher throttle , this problem is there...."

Sorry to hear it limping. Phantom/parttime bogies are the pain. The gradually worse part combined with start-off stumble and your other symptoms sounded just like my first FWB. In my case = intake leak(s). The oil-scummed front and rear made me go after the intake. The compound on the china walls looked like sun dried worms. So, simply reseated the intake and it improved immensely. I also replaced about every hose under the hood, and poured over every point in the off-idle stumble stickie for more PM items like you.


Spray some carb cleaner on the china walls running and randomly around the motor and see what happens eh.
 

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Discussion Starter #3 (Edited)
i might buy a smoke machine and find the leak (if there is any). or puff on a cigar and blow it into the intake to find a vacuum leak.


Vacuum leak was one of my guesses early on also, you might be onto something there.
 

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lol reminded me of the term "chuggle" from the '70-'80s. Some more brain burps over morning coffee:
fubared TCC in the tranny
clogged/loaded air filter
whatever relay or somesuch controlling advance that's corroded/wore out (not that there is such in an LT- but WTH)
that nylon hose connector that rots in front of the tank and whatever other solenoids/stuff related to EVAP
that tiny orange grommet rots under the rectangular thing on top of the intake (everybody gets the Harley Dav. replacement)



The above are more or less stretches or broken record around vacuum related, but the part about setting 7 years is pointing most in that direction. Reading through the entire off-idle stickie years back included some unexpected issues in addition to normal gummed up regular PM stuff. Also, surprised your datalog is coming up blank. Curious whatever might happen from a cracked manifold hidden under the shield?


Good news you at least don't got a no-start, but still good luck finding it. Keepus posted.
 

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To find a vacuum leak, put water in an old ketchup bottle, and add a few drops of dish washing liquid in the water. Squirt the liquid on the vacuum hoses, and anywhere else that might have a leak. If there is a vacuum leak it will suck the liquid into the leak.

Check your PCV valve. It is notorious for causing weird symptoms and not throwing a code.
 

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To find a vacuum leak, put water in an old ketchup bottle, and add a few drops of dish washing liquid in the water. Squirt the liquid on the vacuum hoses, and anywhere else that might have a leak. If there is a vacuum leak it will suck the liquid into the leak.

Check your PCV valve. It is notorious for causing weird symptoms and not throwing a code.

I am gonna try your dish soap leak procedure trick ...
 

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Symptoms sound like a vacuum problem.


Another possible source, especially considering the 7-year sit: the IAC valve's plunger will gunk up and prevent sealing, even if the IAC motor is functional. Gotta follow the service manual instructions to remove/install, so you don't mess up the IAC's electric motor, but it's easy to take off, test, and clean it up along with the hole/passages in the throttle body. After 24 years the IAC is going to have some crud in it.



You say it has the problem at idle and reverse, and I'm guessing it does on the highway even if you're not in OD (shifter in 3), so it doesn't sound like the TCC. I had a bad converter lock-up in a $1000 Jimmy, and it would buck like crazy when letting off the gas, then finally drop out of OD with a huge thud slowing to a stop. Keeping it out of OD on the highway "solved" the problem at the expense of gas mileage.
 
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