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Old 08-07-2014, 03:27 AM   #1
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Default interesting "stumbling" problem 00' impala

hello all. let me start by saying that i have not experienced this problem myself.

lauren has been complaining that when she goes to accelerate to merge onto the highway the car seems to stumble and jumps between 1,000 and 1,500 rpm with a steady planted foot. (around 1/2 throttle or so)

my first thought was TPS, or MAF. so i promptly hooked up my scanner and set it to live data. the MAF is almost identical to my car (also 3800 sII) and the TPS is perfect (atleast when i tested it) no jumps or dead spots at all. it will read down to the 0.10% and it read every tenth of a percent. one thing i did notice though, is at idle, it reads 0.4%. my car reads 0.0%.

another thing i noted, is that if you very quickly floor it then go to zero throttle the car actually almost dies trying to recover. similar to the way a cold carbureted vehicle would. so much so, that the lights actually dim from dropping so far in RPM.

i could not make it die dispite trying this floor it let competely off for over 5 minutes. the fuel trims are also good, at idle it occasionally drops to -0.5% but i checked the FPR and it is not leaking. -0.5% was the largest negative number.

i plan to road test it on friday, but i figure she is about as accurate as i am going to be able to be in explaining the problem. any help is much appreciated!
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Old 08-07-2014, 09:45 AM   #2
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check the fuel pressure and plugs, look for crap on them. kinda what my inlaws lesabre felt like when he had the lim/uim issue. the plug on cylinder 3 was blackish and only half working. how old are your plugs, wires? could also try squirting a fine mist of water in a dark area along the wires and look for arcing
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Old 08-08-2014, 01:46 AM   #3
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plugs are less than a year old. wires are unknown. i have a spare set i plan on swapping in tomorrow. took it for a test drive and it didnt seem like there were any issues.

i did compare her car to mine... i took off the engine cover, went to full throttle, then let my finger slip off the side in less than a second. her car seems to stumble and takes a second to recover. mine revs up to probably about 1100 rpm a half second after i let my finger slip off.

im going to replace the spark plug wires tomorrow and see if that helps. hopefully it fixes it.
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Old 08-08-2014, 08:17 AM   #4
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take a look at the plugs while you are there, looking for black stuff on the part in the engine
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Old 08-10-2014, 01:31 AM   #5
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well, i replaced the wires and it seems to be running well now. should have replaced them when i did the plugs. it still had the original wires. that was stupid of me. ill update if it acts up again.
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