Bucking Cavalier

[tracker_66]

Hi, first of all I just wanted to say I'm a noob, but I do have some experience with car repair and 2nd-Gen Cavvies... I've got a problem that's gotten me totally stumped!

I have a 1994 Cavvie VL 5-sp. that I've owned for two and a half years. I bought it with 77,000 miles on the 2.2L engine and I currently have 119,000. This issue I have has been plaguing me since I bought it...

While maintaining a steady speed, I frequently get a rapid bucking that seems like a misfire. Acceleration and deceleration are normal, except for a severe bucking during acceleration when cold. To date I have replaced three throttle position sensors, a head gasket, spark plugs five times, new wires, coil packs, higher-flow muffler, fuel and air filters, etc. My EGR valve moves smoothly, I've cleaned the IAC valve, use injector cleaner frequently, and I've changed brands/grades of gas but all of these do not help. Well, every tune up I've done has reduced the bucking when hot, but it never disappears and eventually comes back to "normal."

Another perhaps unrelated symptom is that I have to "prime" the fuel rail by turning the key on and off multiple times when the car gets below 1/4 tank, even if it has just been running.

I'm at my wits end with this, can't really afford to have a dealer diagnose the problem, and don't want to keep throwing parts at it until I find a magic cure. Has anyone else had this problem, and does anyone have any ideas on how to fix it? I love my Cavvie, it's a great little car and has never broken down on me, and I will drive it until it's dead... I just want to make it run decent again! Thanks!

[i3o2Matt]

i'd ohm the wires to see if they are in good working condition or not...i kno, i kno, you have replaced them, but dont forget--new parts do not guarantee proper working condition--always check new parts.

it does sound like an ignition problem...unfortunately, you have OBDI, so i doubt you can attach a scanner to it to see which cylinders are misfiring, but i dont remember if you use the waste-spark method or not...if you say you have replaced coil packs, then i'd assume so...

i had an issue kind of like this recently and it turned out to be a dead wire...i had it for about a year and it went dead for no apparent reason...so yes...check parts.

[tracker_66]

I indeed have replaced wires, I'm on my fifth set since I bought the car. I've even changed brands (from Xact to Autolite), and it's always the same result.

Another thing I forgot to mention is sometimes during prolonged acceleration (i.e. merging into freeway traffic) the car begins to hit a plateau around 2500 rpms. If I release the accelerator an inch or so and then get right back on it, and sorta "feather" it this way during hard acceleration, the car takes off really well.

[S_chevy]

Sound like it could be a fuel pressure problem, like a fuel pump going bad or a bad fuel line.

[420_4life]

I have a 94 cavalier and recently replaced one fuel injector that was leeking, the car bucks now when idling and sometimes at speeds around 70 km depending on how much gas it gets. it bucks in all gears, park and neutral doesnt shake the car much but i can still hear the engine as if its misfiring, when its in drive with full break applied it bucks pretty good

any suggestions?

peace
jack