RPM drops while accelerating

Strange problem with my '92 buick park avenue. I was having problems with it cutting out while i was driving, but after replacing ignition module/coils/maf/tps/battery/camshaft and crankshaft sensor (crankshaft sensor seemed to do the trick), the car has stopped cutting out (for now).
I still have a problem ive had for a couple of years. When im driving in the 30-50pm range and steadily accelerating (lightly) i will have a sudden drop in RPM/ and power - i notice it will for example go from 2500 to 2000rpm even though i am pressing on the gas pedal. There is a slight sluggish feeling - and then about 2-3seconds later rpm and power return. Its quite annoying - i dont feel secure driving the car. Anyone have any clues to this? Couple notes: 112k on 3800 engine, did change the headgasket about 1.5 years ago (i first noticed the problem about 3 monthes before the headgasket change). Still has original plug wires, plugs are 1.5 years old. Everything else on car seems to be ok. Thanks!

is it shifting into the next higher gear and then back down?

I know exactly whats wrong. The plug wires are 12 years old. They wear out easily, I'm surprised they've lasted so long! Replace the plugs, AND wires, and you'll be good to go.

If there still is a problem, I can only think of a tranny problem.

Thanks - ill try replacing the wires/plugs this weekend - will let you know how it goes. Hope its not the transmission. Mike

hey, i got the same problem...i have no idea why it would do this...im thinking maybe something is wrong with the 4th gear overdrive or maybe the computer is faulty i dont know im gonna take it to a tranny place and see if they can find the problem...i will check back if i do..

the tranny problem I referenced to is a destroyed 4th gear. My cousin towed a trailer with his 91 park ave, and it would mess up in overdrive. he told the sap he sold it to that the D with the circle around it was for driving on a turnpike.

Well replacing the wires definitely helped the overall performance of the car - but it still has that rpm drop, acceleration hesitation issue. I examined it closer and it seems to mostly happen past 40mph, and i noticed that as im pressing the accelerator, the rpm will drop - and it will sort of 'plateau' at whatever speed its at. It wont Drop speed, just RPM drops, and mph stays there. If i let go of the gas and then press down again it will come back and continue accelerating, with RPM rising. Pretty strange. Opps123 - if you take to the tranny place let me know what they say. Ive got some other issues to deal with rightnow - brakes and now my brakelights/turn signals arent working. You have to have alot of patience with these babies!

hey, i took it to the trannny place, the tech said i have a bad missfire which just started to happen yesterday (when i took it there) so he said get the misfire fixed that should be 90% of the problem, hopefully they can figure this out...thanks again

Hi - anyone know what causes this misfire? May be the same problem as mine - as i forgot to mention that when i have the car parked and idling, if i rev it up press hard, it will stay revving strong and then i will hear a Loud pop sound, like i guess a misfire. Maybe this is what happens when i get into the 40mph+ area. I replaced plug wires- plugs are only about 2 years old - any other ideas? Thanks

my problem with the misfire was my ignition coil one of the cylinders wasnt getting enough spark..i switched out the coil no more misfire but i still have the problem with the rpm dropping i dont know what i could be hopefully nothing too big..thanks see yah

Hi - anyone know what causes this misfire? May be the same problem as mine - as i forgot to mention that when i have the car parked and idling, if i rev it up press hard, it will stay revving strong and then i will hear a Loud pop sound, like i guess a misfire. Maybe this is what happens when i get into the 40mph+ area. I replaced plug wires- plugs are only about 2 years old - any other ideas? Thanks


My 92 has the same problem. My mechanic tried for a month to resolve the problem and finally gave up. He even took it to the local GM shop and they could figure it out either. I would love to know the answer to this one.

Hi guys I am the owner of a 96 Lesabre Limited which has the same issue, my car is always interstate driven and currently has only 81,000 miles. I have read countless posts reguarding this same issue all over the US and Canada with miles as little as 30,000 however nobody ever seems to post a "fix" or cause of the problem. I have not taken mine into the dealer yet $$$ for a diagnosis. This just seems to be a common problem with Buick and the 3800 engine or is it a design flaw???


HELP!!! :banghead:

I had the same thing happen, along with a missing engine when I accelerated, I changed the plugs and wires and now when I push down slowly, the rpms stay the same until I push down more sharply... no drop in rpms at any time, I am thinking some sorta vacuum issue??

Ive basically got most things on my car fixed - and shes working great now - EXCEPT for this annoying drop in RPM when accelerating issue (more details in below posts). Anyhow know whats up with this? If i could figure this out i could Perhaps meet that Nirvana of actually not having a problem with my baby Buick for a few weeks (wouldnt that be amazing!?). Right now she is driving great - but wish it wouldnt do this hiccup thing as im accelerating. One time i was so frustrated i just crammed the pedal to the metal - and boy did she wake up and Go Fast - i was surprised she oculd have that much kick. But alas the strange drop in RPM issue is still there. I think i might ahve to suck it up and bring it ot a dealer - i like to fix most things myself. At least shes working well enough now that i can use her as my main car and restore my '64 galaxie and not drive that gas hog around. Mike

While holding steady pressure on the gas at 50mph, lightly touch the brake with your left foot. This will dis-engage the Torque Converter Clutch. Note the rpm raises. When you release the brake, the TCC will re-engage. Is this what you are feeling?

Hells Bells, Jed Rule - you seem to have something there! I tried out the idea of tapping on the brake with left foot while i noticed a drop in RPM - and sure enough the RPM will spike for a moment right when i do that. For example if im going 30 or 40 or 50mph (seems to have some range) and i notice the rpm drom from 2000rpm to 1500rpm - if i tap on the brake at the same time as i have the gas pedal down (while the car has kind of plateued in its acceleration) i will notice it spike back upto 2000rpm. So it appears that the TCC is very much involved. I have no knowledge of this device - does it mean its having a problem? You seem to have an idea as to the problem - pray tell. Im a pretty good shady tree mechanic - have fixed alot of things myself though in no way an expert - is this something i should be able to fix? I have access to a lift and a million tools (my buddies place). Mike

The Torque Converter Clutch is applied by fluid pressure which is controled by a solenoid located inside the transaxle.The solenoid is energized by completing a circuit through a series of switches and sensors.

There are a number of things to check that affect the trans operation.

TPS - provides throttle position data for determining when to shift or engage the TCC.

Vacuum modulator system - senses changes in engine load. Check for more than 17 in vacuum at the modulator with hot engine running in drive.

VSS - Vehicle speed sensor provides speed data to PCM for determining when to shift or engage TCC

TCC brake switch completes TCC engage circuit when pedal is released

Transaxle temp switch determines shift patterns during high temp operation. TCC will not apply until engine temp reaches 140F

To test the TCC solenoids ( and the A and B shift solenoids) without a scan tool you can read the resistance at the trans axle connector. I can give you more info if this is the route you wish to take.

You will need a scan tool to check for transaxle codes or properly evaluate the sensor readings.
You may also want to test the trans line pressure to verify the internal condition of the unit.

If a shudder occurs while TCC is applying the problem is within the transaxle or torque converter. Something is not allowing the clutch to become fully engaged or is trying to apply and release the clutch at the same time.

If a shudder occurs AFTER the TCC has applied most of the time it has nothing to do with the transaxle. Unnoticed engine problems become noticeable due to the lock-up between the engine and trans. Check the usual suspects with regard to engine missfire, to avoid unnecessary transmission repairs.

I hope this helps. I worked 27 years as a service advisor for GM and am familar with the operation all vehicle components. I would feel comfortable performing these tests but I wouldn't attempt to take a transmission apart. Leave that to the pros.

yes that is what i feel i figured it was the torque converter locking up but what can be done to fix this?>

The torque converter locking up is normal for your car and doesn't need to be fixed. It's functioning just like it's supposed to.... mine does the exact same thing like you described. The tcc will lock only in your highest gear and when the transmission fluid pressure is correct. Yes, it can be annoying having the sluggish engine feeling. Just give it about half throttle and it should unlock. If it's really bothersome, you can wire a toggle switch to the tcc. Just make sure you engage it when you're driving at highway speeds or you'll overheat your transmission.

I had the same problem with RPM dropping going up a hill on my 97 buick lesabre. I read the posts above and decided to just flush my auto transmission fluid and see what happens. paid $140 for complete flush of transmission fluid, replace filter and gasket, lube guard. The problem went away and I don;t hear the shudder anymore... happy ending in my case :)

mine does that sometimes too.. depends ont the situation ( 92 PA SC) but from what i saw, if you happen to step on it while the torque conveter is locking up it will not unlock the millisecond you step on it.. it will first lock and stay there unless you let go the gas and then step back on it.

i think this is normal .. and surely enough the torque will around 50 MPH. i find it annoying that the torque locks so low and then the rpms drop to 1400... geez.. when i drive around town i put in in D .. not OD... so i dont get that annoying thing happening too much.

btw,

i found out that a chip in the ECM will cure this problem by putting the lock up at 55- 60 instead.. and remove the speed limiter at the same time.

zooom zooom

i might buy this heheheheh i'll keep you posted :)


Deadring