well the 95 sc400 I just purchased was bucking a little on light throttle...then buckin alot...then bucking all the time!

eventually I would get a check engine light on deceleration that would go away when I'd accelerate. the code was 31 (low voltage from MAF). I tried cleaning the MAF and that made the CEL come on permanently.

Well I have since replaced the MAF and it is no longer bucking (so far) and Lord willing it won't anymore.

In the process things I did that did NOT resolve it but needed attention anyway...

New plugs
New wires
New Dist cap and rotors
New battery
Replaced a few worn vacuum lines

Now though a problem that has been ongoing since day one is an engine vibration that I feel primarily at 40-45mph...and the car literally bounces while it's idling but rpm's are steady and where they should be.

I'm thinking either Engine mount(s) transmission mount (I have one waiting to be installed) and more related to the 40mph problem rack bushings are waiting to be installed also.

 

I haven't had the problem in a long time. Every once in a while, I'll get a very slight buck/jerk but nothing like it used to be. The maintenance I had on it might have helped or fixed it but I'm not really sure, because a few days or weeks after I had the maintenance done, it did a HUGE buck/jerk and a few other minor bucks/jerks but nothing in a long time.

A few other possibilities I was wondering about was clogged, old cats or something to do with the intake.

BTW, what's the MAF?

 

MAF = Mass air Flow sensor

and funny thing I honestly do think my cat are screwed up...they rattle like crazy and when i rev it sounds like crazy backpressure.

 

Does it seem to do it more when the engine has just started and is cold(er) than when the engine is warmed up to you? Right when it goes into 3rd? at 40 MPH, so not sure if it has anything to do with the gear change. Before maintenance, one time it idled bad, like it was about to die, felt a big vibration that vibrated the whole car, maybe it's related to the buck/jerk, don't know. The one massive buck/jerk I experienced, my car went up and down so hard, seemed like the front bumper could have touched the ground. I thought I was stalling and the car was going to die but it didn't, scared the hell out of me.

 

well the bucking was at almost all speeds...it mostly happened when I'd start to throttle lightly after decelerating. The hesitation / vibration (but definitely not from the road or suspension) is dead on 40 mph like you said.

 

it might be the cat. cuz when i was on a impala forum, cuz of my old car, the ppl wit clogged cats said they where accelerating hard but it wasn't going anywhere and then it would bang into the next gear when it did. so...might be? they said to check it, go to a exhaust shop and get some kinda test done to check for it.

Peace out

 

i have same problem i disconnected my MAF and my car runs great with out it. looking for a new one..

 

if u disconnect it does it give u a CEL?

Peace out

 

hmm.. iono but i guess you can try seafoaming :].. might clear out your bucking problems.

 

well here's what I have gathered today...

my cats are not messed up...they are actually pretty healthy. the violent rattling I had was from a really loose bolt back at the Y in the exhaust. The hesitation I believe is from a very audible exhaust leak up by the passenger cat.

I replaced the tranny mount this afternoon (found the loose exhaust bolt while down there) and due to the way the tranny sits about one inch higher (old mount collapsed) I think the engine also is situated alot different exposing the leak around the headers.

I also have a feeling the engine mounts are pretty messed up too.

 

Did you ever look at the TPS?

 

yea I loosened the bolts and turned it as far clockwise as possible but that didn't help. The bucking has stayed away still since I replaced the MAF.

 

i meant testing it, not adjusting it. My TPS was busted and i had similar problems. try taking a whack on the tps body with the end of a socket wrench (dont break it or something). It cleared mine up a lot; not perfect though. Once i replaced it, it worked fine.

 

Bucking at 40MPH is 100% MAF issue. How I know this you ask? I was leaving an arby's one day, and it bucked at 42mph. I was like WTF is wrong? I open the hood and notice that my Air filter had fallen off the mounting. I reattached it, and bam back to normal.

 

I think your car was just dry heaving cause of arbys...lol