Seriously bucking under full throttle

[Mad Cow]

I don't know when this started, but my engine bucks and jerks really badly under full throttle, especially at low RPM's. I've read that a bad TPS could cause bucking under deceleration, which it does too to a lesser extent. What I don't understand is that I pulled this TPS off a 626 that ran really well and smoothly. I adjusted the idle switch with a ohm-meter and feeler gauges, but that didn't help much. Did I screw up adjusting it?

Also, I'm getting codes for my O2 sensors (unplugged because they're so fouled up it actually runs better without them), and the VRIS#1 solenoid. Could that have anything to do with my problem? And which VRIS is #1? The one with the white or blue sticker?

[Ryan]

You could be running uber rich/lean b/c of no O2's. Thats the only thing on the ehaust side that tells your ECM how it's doing with the fuel ammount. VRIS shouldn't change much except powerband

[Mad Cow]

I guess it could be that, but I always though they were for pretty much just fine-tuning the mixture.

[Nd4SpdSe]

I'm trying to think if the ECU doesn't care about the o2's @ WOT

[marcdh]

yea doesn't it go open loop? Apart from the likes of the knock sensor, clt, iat, I think it just goes open loop - no feedback from o2s.

[wytbishop]

Still...if you know you have bad O2 sensors wouldn't you just replace them?

[Mooneggs]

maybe a fuel issue? bad FPR or clogged fuel filter or injectors?

[Mad Cow]

I'm gonna replace them soon anyway, I was just asking if maybe it was something else. I got a set of injectors and and FPR mounted to rails from solo-ryder a while back, so I assume they're good. Maybe the fuel filter, but it only started doing that suddenly after changing the timing belt, I tried re-timing it again after and it made no difference, so it's not that. Could it be a clogged cat?

[Whisper]

So it started doing it after you did your timing belt and you're wandering if it could be a clogged cat? Unless your old timing belt somehow got sucked into the cat, I doubt it.

[Mad Cow]

I know it sounds stupid, but that thing is, it ran stupidly rich for a while after that a flooded more than a few times because I damaged a coolant temp sensor while unplugging to to get the wire out of the way, and I heard that can seriously screw up a cat, that's probably also what ruined my O2 sensors. I replaced that sensor and it's pretty much fine now.

I'm just throwing ideas out there because I honestly don't know what could be wrong.

[Mooneggs]

what about your timing belt tensioner - did you replace it or are you sure it's working?

[Mad Cow]

I replaced it, it was knocking a bit before.

[projectzemx3]

my friends klde pgt has bad o2 sensors and it bucks hard under accell sometimes. you are probably right about the oxygen sensors being the problem.

[Mad Cow]

I guess I'll try that, also, I just realized it can't really be a fuel or air problem because it gets better at higher RPM's, it's worst around 3-4k.

[Mooneggs]

I just had this issue where I was driving and I had major hesitation, etc ONLY between 3-4k and my tach needle was going crazy... it turned out that something was wrong with my distributor - I haven't tested it yet but I believe its something to do with the pickups inside.

Make sure your disti is good or at least not too far advanced or retarded