Looking for anyone with some tech exp on this matter. A couple fo weeks ago, I got a strange "bucking" coming from the car , at light to moderate throttle, when it's "cold" (first 10-15 mins of driving), and then it'd go away, as the days went on, the bucking comes back everytime I drive and lasts a bit longer, and the more I push down the throttle, the harder it "burbles" or bucks on acceleration, unless I go WOT, upon which it disappears. A couple of days ago I get the codes for the 02 sensors and so I figure "ah ha!" that's the issue. Well, I get the factory replacement pre cat 02s for dvr and pas sides, change them out as well as the #6 fuse and reconnect the battery..CEL is gone, no code...great...take it out for a drive...starts bucking again at partial throttle and CEL flashes (before it came on and stayed on until the battery disconnect). I drive for about 10 more miles and CEL goes away, car is driving better, only slight burble now on accel. I park it, let it cool down, go out again and the burble/bucking comes back, but not as rough as before and no cel. Whats going on here? The only thing I notice thats slightly different is a "rich" smell coming fromt the car when parked and idling. The only mod I've done is the VR TB spacer, but it was having the problem, only less so, before it's install. Anybody with any input? You think maybe the car is running too rich, caused the 02s to clog and throw codes and now it's happening over or you think it's something else? Maybe bad gas? I've filled up at the same station the last couple of times, but there is a rumor that the station is putting reg (87 oct.) in all the tanks instead of midgrade and premium.. could that be it and how can I test the fuel?Any input is appreciated. Here's the kicker, I ran it at the track well after this bucking started and it performed great, 127mph in the 1/4 but slightly higher ETs than normal. After a few WOT hits, the burble/bucking goes away, but I can't go out all the time I drive and nail it a few times before I go out into traffic....

 

Have you ran a log? If the CEL comes on there should be a code displayed. Also your log will show which cylinder/cylinders is misfiring.

Did you make any changes just before this started? Almost sounds like plugs or plug wires. Wouldn't think 87 octane would cause this. Normally the ECM just plugs timing and only at WOT with low octane fuel.

 

Larry...I don't have a scanner/datalogger...used a chepy A.Z. OBD2 to scan for the 02 codes, got two codes, basically saying the same thing, bad sensor bank 2 or bad fuse/curcuit for bank 2. Checked all connections after the 02 re-installation, checked the plug wires, boots, all seems hooked up properly, but if issues persists, I'll pull the plugs and check them out as well. Stange thing, after a 1 1/2 hour cool down, I took it out for a spin and back and the issues is almost 100% gone now, but I'm gonna try to replicate it after a night of sitting, if gone then, maybe it was just adjusting to the new 02s. The only thing I've done mod wise since this first occured is a TB spacer, but I checked it for leaks as well and no issues. I'll keep you posted as to what I find. Thanks for the input!

 

Let us know what you find out.

Wow! Running 127 in the 1/4 without a tuner. You might have a good shop doing your tuning but you might run even faster with fine tuning yourself. Sure would be easier to located this problem. I have HP Tuner myself.

 

Possible umetered air leak and or dirty/failing MAF. Could be a number of things, just start ruling them out one by one.

 

1.8: checked the Tb/Tb spacer and maf, all is good, clean, and free of any obstruction ,debris or oil. Also checked the seal of the tb and spacer and it's tight and looks good. I may remove the tb spacer and give it a try if the problem comes back tomorrow, just to see if the spacer exasberated the problem.

 

Update on the issues: Last drive yesterday, CEL was gone and slight bucking at low to mid throttle, but much better than previous to the replacement of the 02s.After sitting all nite , got in this morn and drove for a few miles, the "bucking" came back , slightly, and only from mid throttle and 30-60mph while accelerating. Went home, let her cool down for a couple of hours, removed the TB spacer, reassembled and went for another drive....problem is 100% gone as of this point, car accels and drives great, no bucking, no issues. Do you think maybe the computer didn't compensate for the TB spacer and was running richer, causing the 02s to clog prematurely? I'd love some input on this. FWIW, because of this, I do plan on swapping plugs withing the next 2-3K miles even if the issue does not return.

 

Bet you had some leakage that wasn't obvious with that spacer. Seal probably looked good but may have had a leak. Good you found the problem in any case!

 

If it comes back, look at the O2 wires. maybe one is a bit loose or slightly burned on a header so that you are not getting a proper reading?