Bucking at low speeds

[Flw Sock]

My festiva has had this problem for a few months now, and I haven't gotten a chance to figure out what it was.

From a stop, when I start to accelerate the front end bucks really hard. Up and down. It's accompanied by a very loud knocking on the passenger side in the front. If I don't ride the clutch the car bucks and refuses to cooperate and run from 1st gear normally. It goes away if I floor it from a stop. Once I get moving (~20mph+) everything goes away.

I took off the passenger side tire today to expect a broken tie rod, loose axle or sway bar. SOMETHING. I didn't notice anything bad. I checked the tie rod (inner and outer), axle, sway bar, and ball joint. Everything checks out. I planned on taking it into the mechanic tomorrow for a diagnosis because as I said before everything checks out with me.

Anybody have ideas as to what it could be? I could still go out tonight/tomorrow morning and see if anybody's suggestions line up.


Thanks.

[sketchman]

Are your trans mounts in good shape? Mine is starting to buck and vibe against the firewall with my engine swap because my mounts are all worn out.

[bhearts]

Mine bucked for a while, it was the throttle position sensor.

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[Flw Sock]

I'm almost certain it's not an electrical problem. It's mechanical. I'll have to check the trans mounts tomorrow too

[WmWatt]

If it only happens when overcoming inertia then it sounds like something which is slipping under stress like, say, probably, the CV joint. Logically it should be something in the driveline, hopefully not transmission related. Doesn't sound like you have time but I'd be inclined to slide the CV boot up the shaft and a look after playing around with the brake and clutch under initial load to see if I could get it to happen. Good luck.

[Flw Sock]

Where are the trans mounts? The only trans mount looking thing I see is behind the oil pan and it checks out.

[sketchman]

Behind the oil pan? Like in line with it? Cause it should be attached to the trans. Both of them should.

They are the only things holding the trans to the cross member. Rear has 1 bolt through the member and the front has 2 IIRC.

[scitzz]

Mine bucked for a while, it was the throttle position sensor.

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DING DING DING Sounds just like it.

The knocking on the passenger side front is probably the VAF slapping closed.

There is an uber easy procedure for testing it.

[Flyin4stroke]

X3 for tps. I've had a car do this. It was very random it would kick out occasionally like it was barely out of whack.

[Flw Sock]

You guys were right. I unplugged the TPS and the car ran way better. I have one on the way. The mechanical sound must've been the VAF.

Thanks so much!! I'll update when I install the new tps.

[NaturalSelection]

Where is the Throttle Position Sensor located? My car will do this sometimes.

[scitzz]

You guys were right. I unplugged the TPS and the car ran way better. I have one on the way. The mechanical sound must've been the VAF.

Thanks so much!! I'll update when I install the new tps.

Hey! Look into just adjusting it, over the years it can move a little bit, there's a thread on how to do it with a multi meter, and shadetree once told me of an easy way to do it by eyeball. I can't recall the procedure off the top of my head right now, but save your money!

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[Flw Sock]

I just bought a new one after unplugging it while the car was running. When I unplugged it, it ran better.

So I replaced it a few minutes ago and took it for a drive. The car is much more responsive to throttle now which is nice, but didn't do anything about the bucking. If anything, the bucking has gotten severely worse. I think it's a mechanical problem. Does anybody know the location of the tranny mounts? Maybe one of those came loose or something.

[Flyin4stroke]

Did you say that it didn't do it when you unplugged it? If it's not in the right spot it will buck.

[Flw Sock]

I didn't drive it with the tps unplugged. I just unplugged it while idling. I'll take it around the block with it unplugged now that you say that and see if it bucks still. brb

Edit:
I took it around the block with the tps unplugged and it still bucked...