mad_7tist: I plan to test it this weekend. I don't have the new sensor yet, so that's all I can do.

look at the press before you worry about the voltage.

OK, I've check some things today.

I have tested the car with wideband, and results are as follows. Idle is 1:13, WOT at 13psi up to 7000rpm is below 1:11. That all sounds ok. I still think it's a bit rich at idle... the rear bumper is black around the exhaust and your eyes start to burn if you stand close to the exhaust...

The bucking. As expected, the AFR turns lean when this happens. So, we checked fuel pressure and f/p hold pressure. Everything read exactly as desrcribed by workshop manual. I couldn't meter the fuel pressure on the road, tough.

Next what I will do will be monitoring the F/P voltage and see if there's anything unusual with voltage. I suspect something is wrong with fuel pump resistor or fuel pump(speed) relay. Maybe there's a problem with switching voltage from 9V to 14V... Or a bad connector / harness.... I think so, because the bucking goes away few moments after I wot it -> probably switching to bypassing f/p resistor? We'll see...

OK, if that doesn't help, then I'm replacing fpr, fpd, iat, wt, ft, prs... I'm getting sick of this bucking...

Altough, it still seems that if I push the car for few minutes in higher revs, the bucking disappears - on the second tought tough, it might be connected with reseting the ecu... I will try this again...

Some update:

I have checked the voltage and pump and everything is ok, neither I have found any connection with rising voltage and bucking.

This weekend I have replaced the waterthermosensor and intake air thermosensor. And the bucking is still there. It wasn't bad at all, because I wasn't testing there through the city driving - which seems to stimulate the bucking the most. I tried running it at idle and simulating stop/go traffic, but it still isn't the same. I managed to get it to some slight bucking (actually more like surge at constant speed and surging at very very slight acceleration). And what is still annoying is the response when I suddenlywot it in the lower rpm range (from 1000 to 3000) - it's a momentarily pause (less than one second) with backfire and then goes away with strong. I don't know what is causing this, but it is seems to me that bucking is just the worst form of this sudden-wot-backfire thing.

Next on the list are fpd, fpr, fuel thermosensor and fuel lines...

I am also experiencing this same problem since installing a new engine. It is not a hard bucking/hessitation and it seems to only happen somewhere between 2k & 4k. It seems almost cyclical as you drive, kind of a surging. It doesn't seem to do it all the time, more when I have warmed up the car and go and drive it again. If it sits over night it seems to drive fine. But even after sitting for 4 hrs or so it will seem to do it. My car didn't have this problem before replacing the engine. I also have a PFC which was tuned by kdr for my previous engine. I will be going there to have it re-tuned for the new engine once I have 1k miles on it. I also had my injectors cleaned when I had them out. I also replaced the cat with a stock one with only 25k miles on it since my original was becoming clogged. I am very interested in determing what the cause of this problem is. If anyone has solved it yet then please respond. It could be one of those issues that is caused by multiple sources and could therefore be very difficult to track down. I am hoping to investigate a few things this weekend. has everyone who is experiencing this problem recently messed with the vaccume lines, replaced spark plugs, had the uim off, replaced engine??? any common threads??? In any event add me to the list of hessitators.

I had this problem and it got completely worse when my Air intake sensor went out. But when my air intake sensor went out, it gave me a check engine light. It went away after I replaced the air intake sensor.

I have this same problem. I adjusted the TPS and installed o2 and thermosensor. these things did not solve the problem. One thing I did notice is that adjusting the idle setting seems to help (somewhat). If the idle is set somewhat high or somewhat low it acts up more than usual.

I'm wondering if adjusting the air bleed screw may help.

I have solved this issue on my car. I took it to KD, they changed the engine wiring harness among other things. I posted a list of everything that was wrong in another thread on this subject, just search for my username to find it. Hopefully this will help someone else.