97 Q45 - bucking saga continues

[pnanda16]

So I replaced the MAF and the occassional bucking while waiting on stop light continues. I have so far cleaned throttle body, replaced TPS as once a code had been thrown, cleaned AAC/IAC etc. The problem has been on for more than 6months without aggravating.

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 lotPhal1997 Q45, 171K Miles, all fluid flush every 2yrs, synthetic oil for transmision and Engine since odometer reading of 35K miles.

[goody90q45]

I'm not sure if your 97Q is set up the same as the G50, but just for kicks why not take a look at your FPCU connection for any signs of burning/melting/scorching. If it's anyhting like the G50 it's easy to get to through the trunk and is on the passenger side under the deck. The FPCU is in the background in the pic. CEL or codes with this one?

[pnanda16]

Will check the FCPU tonight, but I believe it might be near left side of the driver seat (will check the service manual).

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.

thanksPhal97Q

[maxnix]

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.

Think it will be self healing?

What is frequency of fuel filter replacement?

[pnanda16]

You mean the knock sensor self healing? :-). It didn't create trouble for smog test. I am keeping that work until something else makes me remove the plenum.

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

[maxnix]

CEL for two years is pretty much abuse. Even if it was working for smog test, it has failed repeatedly during operation. Usually their death throes only last a month or so.

[bullittandy]

Its a bad coil, search around and you'll find some other threads.

[Garage Battle]

Bad coil possibly. While the car is running, unplug one coil at a time to see if it makes a difference in the way the car runs. Whichever one you unplug that makes no difference is the bad coil.

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.

[maxnix]

Bad coil possibly. While the car is running, unplug one coil at a time to see if it makes a difference in the way the car runs. Whichever one you unplug that makes no difference is the bad coil.

Better to switch the indicated bad cylinder coilpack with another non code throwing one.

[sdkhalsa]

Before going after the individual components in the fuel delivery system, I would recommend teeing in a fuel pressure gauge and placing it so that you can see it while driving, i.e. under windshield wiper. You can note if the pressure holds while the bucking is happening. What is your mileage? Joe at Scottsdale Infinity tells me that at least on the G50 model the fuel pump tends to fail at the 70-100K range.

[powrserj]

I been having the same issues for about a month now changed the Fuel Pump couple days before and now I am fine for now.....