I just nothiced something that might give a clue.
* The bucking is much more frequent when the fuel tank is in the last quarter and lower.
* When tank is full, the bucking is very very infrequent and milder.
* Also when AC is on, chances are higher for bucking to appear.
* I believe the problem might have started the last time I asked a mechanic to replace fuel filter - it might just be my paranoid thinking.

I have antother question. I am in 'D' while waiting on a stoplight. If AC is ON, should the RPM drop or increase slightly to account for higher load? I think I see intermittent behavior. Sometimes, when I turn on the AC while at stop light, the RPM goes up - I don't believe I ever see the bucking appear. But sometimes the RPM drops (by 100 or 150) when I turn on the AC and chances are much higher for the bucking to appear.

Two areas:
(1)
Does this recent finding narrow the problem to possibly in the fuel delivery section? I dont hear any sound from fuel tank, the freeway and other driving doen't have any problems - i get good throttle response and power. Fuel MPG is same as well. From the fuel pump to the fuel injectors, what are the different parts where a failure can occur? Any cheap parts to replace and see if it makes a difference?

(2)
RPM drop issue when turning AC on. Is that a problem with the IAC now listening to computer instructions for inceasing idle air requirement?

Thanks for all help. Other than this bucking problem, everything is running great and I am not going to give up on this.

thanks a lot
Phal
1997 Q45, 171K Miles, all fluid flush every 2yrs, synthetic oil for transmision and Engine since odometer reading of 35K miles.

94 Q45 160,000 miles.........................................90 Q45 237,000 miles

CEL is off, the only code it has thrown repeatedly is P0325 which is the knock sensor bank 1 that I am aware of for at least 2yrs now.

thanks
Phal
97Q

What is frequency of fuel filter replacement?

Discover the power of the button!

I replace fuel filter every 1yr or so. Going to do another tomorrow.

Now if not that, it could be a malfunctioning EGR (dirty) or if the q45 has a BPT valve on the EGR assembly it could be malfunctioning, dirty, or have a old vacuum hose thats leaking.