Shake+Bad Fuel Mileage [Archive] - Forum


View Full Version : Shake+Bad Fuel Mileage

01-21-2004, 02:09 PM
Ive posted a few threads on this, none have gotten much of a response, so Ill post again.

Im getting a shake (car vibrates, rattles change in my cupholders) above 40mph in top gear. This does not occur in any other gear. I just had an alignment last week, didnt help a bit. Im assuming that my transmission is going (99,000 Miles as of today). Any ideas? I havent changed my spark plugs in the last 20,000 miles, or the fuel filter in the last 20,000 or so either. But, if those were the culprits, wouldnt i get a vibration all the time? I can sit in my garage and rev it to the rpm's that its usually at cruising at 40 and up, and I get no vibration. It only happens in top gear, under no to light loads, from 40 MPH and UP. Used to only be from 40-50, now its 40-90 (as high as I wanted to test it), although it is definitley worse at 40 than at higher speeds. Any Ideas?

Dealership has no clue what It could be, im hoping someone has similar experience and can help me with the diagnosis. Again, its a '99, 99000 Mile, 2.4 with the 4t40E automatic. THANKS


01-21-2004, 02:27 PM
Tire could have thrown a weight and is off balance, it won't show it till higher speeds.

Ice in the rim will also throw the balance off and cause a good shake.

01-21-2004, 04:36 PM
Wouldnt it then vibrate even if i downshifted? I can do 40 plus, but in third gear, and get no vibration at all. It only happens in 4'th for some reason. Thanks for the ideas though. It started about 3 months ago, and since then has had new tires, and an alignment. Stupid Car.

01-21-2004, 04:37 PM
hmm, could have a broken tooth on a gear then.

01-21-2004, 06:22 PM
possibly motor mounts maybe. in my jeep it would vibrate when it shifted into overdrive and we replaced the mounts which were worn and it cut down on half the vibration, the other half was from an out of balance front driveshaft.

01-21-2004, 07:51 PM
Wierd. Its too bad not many people here have the engine/tranny I do. I wonder if it could be transmission mounts?

01-21-2004, 08:00 PM
Do your RPM's drop when you experience this shaking?

I had this problem at about 50 mph... rpms would drop... shaking.. would let off the gas the hit it again and it'd be gone. I was getting horrible gas mileage too.

I didnt notice the rpms dropping until i considered a misfire problem. I never got a SES light so I didnt know what to look for.

My brother's car is doing the exact same thing as you explained. Car has 120k on it and doubt the plugs have ever been change.

The thing is.. i dont see why your plugs would go bad at only 20k.. interesting..

01-21-2004, 08:18 PM
Well, they are Denso iridiums!:D So you think its the plugs? If so, Ill go buy me some good ole delco's tomorrow and see what happens. It just sucks, I have class every week day, and its about a 120 mile round trip! So, I drive a LOT.

I also have a gently used MSD DIS 2 on the way, pre-wired for everything that I need. So, if youre thinking its the plugs, maybe with the new plugs, plus the MSD, ill be a happy camper. I HOPE its the plugs...

01-21-2004, 08:19 PM
PS, the engine sounds like the RPM's should be dropping, but the tach doesnt show it.

01-22-2004, 08:51 AM
If it's fine in 3rd gear at 40 mph, but it's not fine in overdrive at 40 mph, it's not your plugs or your wheels or your tires or your suspension or anything like that. Looks like you have a trans problem.

01-22-2004, 09:13 AM
Torque converter lockup selonoid? Perhaps...

01-22-2004, 09:15 AM
Maybe if it was rapidly locking-unlocking.....

01-22-2004, 10:42 AM
So Dave... got any updates for us??

lol this is off topic...

is it just me or does 71z28rs and atc3434 travel as a couple to threads? lol Not flaming... you guys both always have good info, just realized you guys pop up and discuss stuff within the thread together sometimes... :thumbs:

01-22-2004, 12:47 PM
Multiple Personalities perhaps?

Went to the dealer today, they wanted 15 dollars/plug, so ill be ordering the online for half that. And, they told me 720 dollars to replace the trans, if I provide one. I often see them on ebay and things with few miles for only a couple hundred dollars.

Now i have to hope the trans makes it to tax return time...

01-22-2004, 01:04 PM
:rolleyes: Yeah... thats weird. If its a split personality, I dunno about it yet! I dunno what it could be that would cause only one gear to shake. And you'd think it woud be worse under a harder load. So, lemme just make sure I understand this... if you drove up to say 70 mph and kept it in third... it wouldn't shake at all, but as soon as you shift into 4th you'd get the shake? In other words, its defintely isolated to one gear, right?

01-22-2004, 01:32 PM
My other personality seems to know what's up. If it's isolated in just that one gear (top gear), I don't see how it could be anything other than the trans.....unless of course the TC lockup is cycling rapidly like my personalities were discussing earlier. I guess that could cause some sort of vibration. And it does seem like it would be worse under heavier load. But, it seems impossible that anything external of the trans could be the issue since the problem is limited to overdrive while moving above a certain speed.

I guess the weird part about it is that it seems very unlikely that you'd damage your top gear before any other gear. That gear sees the least abuse. Maybe a defect in one of the planetary gears or syncros or something....sounds like something is out of balance....

Good luck with that and let us know how things work out.

01-22-2004, 01:40 PM
Thanks guys, I really appreciate the input.

Yup, if i kept it in third, I get no vibes. Let it bump up to fourth, and im shaking. Do you think eventually it may spread to other gears? Im not to up on operation of the 4t40e peice of crap...

01-22-2004, 01:46 PM
From what it sounds like, it shouldn't quickly spread to the other gears. But to be brutally honest with you, it isn't exactly good for the car. Anytime you have something that rotates at high speeds that is vibrating off balance, you risk causing extra wear to mating parts. If the whole car is shaking because of a misbalance of the trans for whatever reason, then you're putting alot of extra lateral load on the engine's crankshaft bearings since the trans is tightly splined to the torque converter and the torque converter is tightly bolted to the flex plate. I don't think I'd let it go for too long before I took care of things. Of course, all that is based on the assumption that the trans is bad.

01-22-2004, 06:35 PM
Again, thanks for the advice! Ill keep you all up to date, and if you think of any other (cheaper) ideas, let me know!

01-22-2004, 07:10 PM
Get your wheels balanced! (cheapest check you can do)

01-22-2004, 08:18 PM
Done along with brand new tires and an alignment a few weeks ago.

01-22-2004, 08:32 PM
Originally posted by Rba007
Thanks guys, I really appreciate the input.

Yup, if i kept it in third, I get no vibes. Let it bump up to fourth, and im shaking. Do you think eventually it may spread to other gears? Im not to up on operation of the 4t40e peice of crap...

Same thing with my bro's car. If its above like 3000RPMs no shaking... but if i put it in drive, RPMs drop to about 2000-2500... then they drop all of a sudden to 1500 and the car shakes to hell!

01-22-2004, 08:35 PM
Did it fix it?

If not: Have you checked your tie rods for wear?

01-22-2004, 08:37 PM
All my suspension parts look nice and shiney (if they werent covered in snow of course). But, if it was a suspension part, wouldnt the vibe continue no matter what gear i was in? if i get up over 40 and drop it into third, the vibe dissapears.

01-22-2004, 08:39 PM
uuuuuhhhhhh.... my guess

did you put it in neutral when traveling over 60?? does it still vibrate... if not then it is not the tires...

if it only vibrates in gear you have 2 causes

bad marriage mount...(mount that mounts the motor and tranny) less stress at lower rpm's...the higher rpm's may make the lose mount undetectible do to the torque on the motor)

bad tranny gear teeth on the 4th gear! does you OD vibrate also?

01-22-2004, 09:10 PM
No vibration in Neutral.

Anything in top gear, under no, or light load vibrates. Its also starting to vibrate under heavier load in high gear.

Dealer told me today that by the time they ripped it apart to fix the 4'th gear, i might as well have bought a new tranny cause itd cost less.,.. I may end up having to grab a remanufactured one for 700 or so, its better than the 2300 gm wants...

01-23-2004, 11:35 AM
I should also add that I dont get a shake until the car starts to warm up. Meaning, as soon as the temp is high enough to start registering on the temp gauge i will get the shake.

02-09-2004, 02:09 PM

Installed New Delco Plugs this weekend, along with an MSD ignition. No change.

Ran seafoam through the car (gas tank, and vacuum line method), no change.

Getting the fuel filter changed, and injectors professionally cleaned wednesday.

Also, I noticed that when im idling, my Volt gauge will dip about 2 volts occasionally, and the engine feels like its gonna cut out. The RPM's do not dip though. Could the alternator be going, and could that have anything to do with my shake? Remember, it only does it after a good bit of driving, and usually when traveling 40mph or up. Any new ideas??????? PLEASE???

02-09-2004, 08:47 PM

02-11-2004, 08:50 AM
bump II

02-11-2004, 09:43 AM
If its only in one gear, its the tranny, not the motor, thats simple enough. Now, what it is in the tranny could be compicated. Mileage should be a tad nicer with a new fuel filter, that defintely makes a difference if they are clogged up bad. Now, is it 40mph and up in just forth, or third as well? Perhaps a torque converter intermitent lockup problem. Just some stuff to think about...

02-11-2004, 09:54 AM
Since it is only occuring in forth and when warm, it sounds like the lock-up converter. The converter will not lock-up until the car reaches a pre-set tempeture.

If it was the tranny itself, it is unusual for the OD to go first. It ususally is 2nd gear that goes first. I had this happen when the tranny on an Eclipse I use to own let lose while exiting a highway. I lost second as it was down shifting and the computer put the car is a sort of safe mode, which only gives you 3rd. Really sucked as the turbo couldn't spool up.

02-11-2004, 10:03 AM
i dont know if this will help you or not, but i had the exact same symptoms as you are describing and i THOUGHT it was the TQ going on me. well, i changed the timing chain when i did some major tune up's to my car, i had 160,000 on the odometer at the time. once i got it back on the road, no more shake and back to the 30+ mpg on the freeway again.

just something to look at because it was a diagnosis in the haynes manual for me.

02-14-2004, 07:54 AM
I take it that you want to keep this car for awhile and have the best experience driving it, but you *could* save the money and just drive it in 3rd, you would lose some gas mileage, but you would save the money on a new tranny or tranny fix.

02-16-2004, 03:14 PM
Ok, just got her back from the transmission shop. Here is what I was told.

Its not the transmission. They dropped the pan, and said it was about the cleanest tranny they'd ever seen. They hooked it up to all their diagnostic equipment, and got no codes on the tranny.

Then they hooked it to the engine. This is what they got (I have no idea what it means):

"Incorrect timing, or temp for closed loop. o2 sensor off back 2"

My second (by the cat ) o2 sensor is only a year old, and i doubt it would cause my car to shake. Remember, the engine hasnt set any codes cause of this shake. Any new ideas? Why would my timing be incorrect???

02-16-2004, 03:59 PM
Originally posted by Rba007
Ok, just got her back from the transmission shop. Here is what I was told.

Its not the transmission. They dropped the pan, and said it was about the cleanest tranny they'd ever seen. They hooked it up to all their diagnostic equipment, and got no codes on the tranny.

Then they hooked it to the engine. This is what they got (I have no idea what it means):

"Incorrect timing, or temp for closed loop. o2 sensor off back 2"

My second (by the cat ) o2 sensor is only a year old, and i doubt it would cause my car to shake. Remember, the engine hasnt set any codes cause of this shake. Any new ideas? Why would my timing be incorrect??? You need to get the code number(Pxxxx).

02-16-2004, 04:56 PM
They said it didnt throw a code (ive had no lights or anything), and i thought if it didnt trip a light an actual code number wasnt stored?

02-17-2004, 07:06 AM
the light only displays codes that are stored in the may have a "error" record in the memory of the pcm.......take it to a dealer so he can scan should cost you 35 bucks

02-17-2004, 03:54 PM
Or bring it to autozone and they will check it for free

02-17-2004, 03:57 PM

02-17-2004, 04:10 PM
Exactly, autozone only reads things that throw lights.

My dealership charges 92 dollars per scan!!!!!!! So, ive spent about 184 there the last 2 months trying to get this problem taken care of. They obviously didnt find, or atleast didnt tell me they found anything either of those two times. Stupid Dealer.

02-17-2004, 06:53 PM
I wish you were right! stupid autozone

02-26-2004, 01:30 PM
First post here! Hi everybody!

I have a similar situation in my '94 except it's becoming more evident in all gears around 2k rpm. At first it was just noticable in 4th at around 70mph (so I'd drop it to 3rd). But now I am noticing it lugging around town to. It basically feels like a tire is out of balance, but we all know that's not what it is.

It's under light to heavy load, completely disappears in neutral at the same speed (engine or road speed), and I haven't figured out a correlation to engine temperature yet (I normally only have a 1 mile commute).

I was just curious if anyone who's been reading this has any advice for me on this or if there were some new thoughts on this problem. I got my Granny for a steal ($1600 w/ 108K at auction) but I am not going to give up on it easily. One thing I noticed when I got her was the tranny fluid looked brand new, and I was wondering if the wrong type could cause something like this.

Any help would be appreciated!


03-08-2004, 02:50 PM
I just wanted to follow up on my own post here.

I swapped out my plugs, wires, fuel filter, PCV valve, and air filter this weekend and the shaking went away!

All signs point to the spark plugs and wires being a major contributor to the "shuddering". They were more than likely the originals. If anyone wants to see what an AC Delco with 108K miles on it from a 3.1 looks like, I'll throw a picture up... NASTY.

In any case, my assumption is since I usually just drive short distances the plugs were getting more and more fouled and the engine was lugging along / practically wanting to stall around 2K rpm. With the older suspension components and crappy roads, I think the engine was shaking it's head 'no' to the task and causing the vibration.

Incidentally, and not surprisingly, I am seeing a HUGE difference in the old Grand Am. It's running like a scalded kitty now. VERY impressed with it!

03-08-2004, 03:53 PM
i think his issue may be bad ignition coils?? you should check those out!!

03-08-2004, 07:58 PM
I replaced all those toys and the problem persisted. Guess I should have updated this though.

Brought the car to a transmission shop about a month ago, they scanned it, and dropped the pan. They said it was just about the cleanest they had ever seen. They didnt do any other work. But guess what, the problem went away after they dropped the pan!!!!! Odd i know, but funny since the dealer supposedly did it twice this fall. Stupid dealer.

03-09-2004, 08:45 AM
hmm, maybe dropping the pan 3 times replaced enough of the fluid to fix the problem.... unless it was the only time they dropped it, then a fluid change could have fixed it

03-09-2004, 03:01 PM
They didnt change the fluid the last time, but did the first two times. Wierd huh? I think its possessed. I need a young priest and an old priest...

03-09-2004, 05:26 PM
The shudder started at what mileage? Just wondering, maybe ill take some miles off that and subtract about 10k and base what mileage I want to have my tranny's fluid swapped at, actually ill probably just do it at 36k

03-09-2004, 05:29 PM
Good idea, then youll have a looonnggg while to go before you get to my mileage! It started at 90,000, im at 101000 now.

03-13-2004, 01:19 PM
Meh, ill just do it at 36k miles then, because im getting a strange whine, i think im going to open a thread asking about it though, could be some other problem in the tranny that wont get fixed with fluid swap

04-24-2004, 02:27 PM
My wife's GT started shaking just as described here. It only happens when in OD - 3rd gear fine. Car just turned 70k - she finally got around to telling me about it - "it's been doing it for a while..." - My wife.

It seems like the torque converter clutch is trying to lock, but it is slipping and can't lock. When the shaking starts, the RPM dips. When the shaking goes away, the engine RPM increases.

I have no idea what to do next. I do not trust any of the dealers around here (every one of them has screwed this car up...), and it seems like the local Aamco shops don't want to touch this problem.

It seems like it could be the converter clutch slipping (either bad solenoid or clucth), or could be that the clutch is locked, and the engine is misfiring. It does seem to run a little rough when in neutral, but nothing outside a normal 3.4L.

Any more feedback/updates from anyone relating to this problem? Thanks!

04-24-2004, 02:47 PM
Have you had the fluid changed?

04-26-2004, 09:38 AM
Fluid was changed at ~64k. It was a change - not a flush and change. The problem has started since then.

I was worried that something would get screwed up during the change.

Did anyone ever pinpoint the cause of the problem?

05-30-2004, 12:15 PM
Anyone have an idea what a new transmission/torque converter would cost? How about a rebuilt unit?

Or... what am I looking at to get this one rebuilt? Just wondering if I should fix or get rid of the car...