My 1999 Q45t with 94,000 miles has a stumble at idle

[ZMARKUS]

Whats happening fella Q owners. Here's an issue Im having with my Q45. My dead quiet exceptionally smooth idle is interrupted by this intermittent stumbling or tremors. It feels like a traveling electric current because I can feel it under me and then I may feel it behind me and by the way no ses light. The rpm needle is dead still during these episodes. This all started around 89,000 miles. The car is beautiful, a chic puller , and runs smooth and strong, which is why I'm anxious to resolve this. Took it to Infiniti of Charlotte and they couldn't determine the cause without a doubt. Their diagnostic machine said all 8 coils were working within specs, although two less than others but still within specs.They were able to pull a code p0330 while running the vehicle but said it was a generic code and only told the vehicle was skipping but not why. My search on this code says knock sensor #2, so whats up with the generic means nothing code talk from Infiniti . These have been my attempts at eliminating the problem with no success but with slightly increased performance.( new fuel filter, trans flush, coolant flush, induction cleaning, new air filter, new ngk plugs, new pcv valve, bg44k added to gas, new diff fluid, added ISO-HEET to gas), and I only fill up with 93 Texaco, Chevron or Shell. Your help is greatly welcomed
Modified by totaljett at 5:28 PM 5/31/2007

[gjh20]

come join us on this thread zerothread/253774. sounds like we have the same issue

[Q_SHIP]

I don't even know why I bother answering these posts anymore because someone always tells me I'm wrong. Even though I had the same issues and it infact WAS the knock sensors and harness.

[maxnix]

I don't even know why I bother answering these posts anymore because someone always tells me I'm wrong. Even though I had the same issues and it infact WAS the knock sensors and harness.

I can well imagine that a bad KS on one side or an intermittant harness failure could cause a similar failure.

P0303 is an OBD II specific cylinder code misfire (#3). Time to start switching coilpacks one at a time.

An intake induction fogging is good for maintaining a clean plenum, but won't touch a dirty (70K miles) one, nor the TB, IAC valve, EGR vavle or the EGR tube.

[miata007]

My 97 has similiar problem. In addition, sometimes it stumble or feels like the engine is shut down for a split second and it goes away. I've replaced both knock sensors since the rodent chewed off the KS cables. Still the problem hasn't gone a way at all. I am afraid its the coils. Which is labor intensive and costly (parts).

007

[maxnix]

007

The coilpacks? Not at all, if you determine which ones are defective and replace only those.

[paranoidjack]

Mine went away 20k miles ago.

Never seen it since.

I did nothing short of overhaul the entire suspension with OEM...only electrical parts replaced were the 2 TCS sensors....other than that, just routine maintenance!

[miata007]

Maxnix,The coils on the passenger sides, access is easy. How difficult is the access to the driver side? When I replaced the KS, the coils on the driver, seems like one has to remove many things before you can get to it (or them).

007

[miata007]

paranoidjack,

The TCS sensors actually have something to do with engine stumbling????

007

[maxnix]

Maxnix,The coils on the passenger sides, access is easy. How difficult is the access to the driver side? When I replaced the KS, the coils on the driver, seems like one has to remove many things before you can get to it (or them).

007

You do, but it is just more time, nothing like brain surgery.

[elwesso]

paranoidjack,

The TCS sensors actually have something to do with engine stumbling????

007

Not possible.

Yeah with the specific cylindre misfire its time to switch coilpacks around like Brian said. KS would probably not cause a specific cylinder misfire, however if they are known bad then you should replace them regardless.

[paranoidjack]

paranoidjack,

The TCS sensors actually have something to do with engine stumbling????

007

No, of course they don't...I was just making a point that it was the ONLY thing I had changed that wasn't metal and rubber. Just went away after she entered my maintenance program!

[db_autotek]

I haven't had any roughness in my Q, but in all my previous cars, rough idle was always always due to: (in this order)

1) PCV valve2) Vacuum leak3) Spark plugs fouled or out of gap4) Spark plug wire burnt up (racing)

Just my 2 cents...

[Q45tech]

The 90-96 Q coils were bullet proof in size and design, the Q41 cost cut redesign was significantly less robust and often problematic in different areas of the engine.

Be very careful about comparing the two very very very different models, just as one must segment the 90-93 and 94-95 and the unique 1996.

Only compare apples to apples year groups to year groups.

[paranoidjack]

The 90-96 Q coils were bullet proof in size and design, the Q41 cost cut redesign was significantly less robust and often problematic in different areas of the engine.

Be very careful about comparing the two very very very different models, just as one must segment the 90-93 and 94-95 and the unique 1996.

Only compare apples to apples year groups to year groups.

Tech-in all these idle posts, I don't think I've heard you 2 cents. What is your guess is the root of all this q41 stumble complaining?

[bullittandy]

X2. Let's hear it tech.

[maxnix]

If one reads all of Q45tech's posts, one will quickly realize that his interest in the economized build of the VH41DE is minimal.

In particualr, he has mentioned many times the cheapened design of the later colipacks.

[paranoidjack]

If one reads all of Q45tech's posts, one will quickly realize that his interest in the economized build of the VH41DE is minimal.

In particualr, he has mentioned many times the cheapened design of the later colipacks.

Duly noted. The question still stands, as I'm sure he would have something more valuable to say than most here *cough*cough*

[maxnix]

We'll see. But he is not too inclined to guess on things he hasn't studied in depth, and his interest in the VH41DE is incidental to some that have passed through the shop, not exhaustive like the VH45DE he has owned, experimented upon and maintained for years.

His depth of knowledge requires time spent in observation he simply hasn't dedicated to the later FGY33 and F50 like he dedicated to the G50. However, his principles are easily extrapolated for those who have the ability, interest, resources and discipline to apply them to other systems. That is why I recommend members of this board for less than 3 years go back and read all of his posts. It is an education easily gained compared to the time and expense of experience required to duplicate it.

[UM97Q4.1]

I have this same problem on my 97. This has been the mystery plaguing my vehicle for about 3 years now. Nobody can figure out what is wrong with it, dealer said it was #8 coilpack so I changed that and had the same problem. I have learned many things since then, such as.

!) it will only do this when it is in drive, put it in park and it stops.2) tends to happen more often when the AC is on.3) when it is really bad the car will hesitate from a dead stop.4) feels like there is a 50% loss of power at times.

I have taken it to many different places and no one has been able to get it to act up (very annoying). I absolutely love my car and when it is not acting up it runs and looks great. Please for the love of Infiniti if anyone knows what this could be I am sure many would appreciate.

[ZMARKUS]

Amen brother! What's the big deal with this issue. It puzzles everyone and even the Infiniti dealers seem to be clueless . The person that resolves this plague will be praised by Q owners all over. Somebody ,anybody, what the f*** is causing it. Whats really weird is that it stopped for a whole two weeks and then resumed . I'm gonna replace that knock sensor#2 code the scanner pulled and if that doesn't do it . I just don't know . Are you listening Q Gods, stop this suffering!

[Qproject]

there were a few people who had replaced their coilpacks (some all 8) with no improvement.

SO IT NOT THE COILPACKS!!!!!!!!!!!!!!!!!!!!!

now that we got that out of the way, what could it be causing this ?

are any of you with this problem getting a CHECK ENGINE LIGHT ?

[paranoidjack]

there were a few people who had replaced their coilpacks (some all 8) with no improvement.

SO IT NOT THE COILPACKS!!!!!!!!!!!!!!!!!!!!!

now that we got that out of the way, what could it be causing this ?

are any of you with this problem getting a CHECK ENGINE LIGHT ?

actually...one thing I did do....I added a can of BG to every tank for roughly 2 weeks. This seemed to help a bit. Overkill maybe, but I bought the car at 72k so you never can be too careful.

[ZMARKUS]

I haven't gotten a check engine light . Not so much as a blink but as I said earlier the scan on my car does have a p0330 code but still no check engine light.

[Qproject]

u mean P0303 right ?

anyhow you guys gotta remember, it could be another problem that is causing that "misfire on cyclinder 3" as the ODB2 code would spit out. It doesn't necessarily mean it IS the cylinder 3.

I haven't gotten a check engine light . Not so much as a blink but as I said earlier the scan on my car does have a p0330 code but still no check engine light.

[maxnix]

(yo)u mean P0303 right ?

anyhow you guys gotta remember, it could be another problem that is causing that "misfire on cyclinder 3" as the ODB2 code would spit out. It doesn't necessarily mean it IS the cylinder 3.

Actually, it does.

Which cylinder do you think it indicates?

Why one starts interchanging the indicated coilpack with a good cylinder and observes whether the next code follows the coilpack or not. If not, one looks at plugs and injectors in the indicated cylinder.

All the above assumes the intake path, EGR and IAC valves, fuel filter and fuel pump. are in as new operating condition.

there were a few people who had replaced their coilpacks (some all 8) with no improvement.

SO IT NOT THE COILPACKS!!!!!!!!!!!!!!!!!!!!!

now that we got that out of the way, what could it be causing this ?

On that particular car maybe, but on others, maybe not, per my preceding comment about the condition of the intake path. Too little information to make an inference.

[Qproject]

WE ALREADY KNOW IT'S NOT THE COILPACKS, a few dudes have already interchanged them all with same results.

SO WE KNOW IT IS NOT THE COILPACKS, geeze

so maybe it's the plug/injectors ? there was a dude that did the BG additive on his fuel tank and it seemed to improve a bit. Now can you start being a little more open minded and start to think a bit.

[QUOTE=maxnix]

Why one starts interchanging the indicated coilpack with a good cylinder and observes whether the next code follows the coilpack or not. If not, one looks at plugs and injectors in the indicated cylinder.

All the above assumes the intake path, EGR and IAC valves, fuel filter and fuel pump. are in as new operating condition.

[99q45t_vl]

In my particular case, the injector #5 and, more recently #2, were the source of the stumble and then misfire. I use only 93 Shell or Chevron gas, had the fuel filter replaced, all regular cleaning (EGR, Plenum, IACV, TB, etc.), and all up-to-date maintenance done (including new PFR5G-11 plugs, PCV, KS, harness, and O2 sensors).

[UM97Q4.1]

In my particular case, the injector #5 and, more recently #2, were the source of the stumble and then misfire. I use only 93 Shell or Chevron gas, had the fuel filter replaced, all regular cleaning (EGR, Plenum, IACV, TB, etc.), and all up-to-date maintenance done (including new PFR5G-11 plugs, PCV, KS, harness, and O2 sensors).

Interesting info, how long ago did you have this done? and it is gone completely, no signs of it rearing its ugly head again. If you dont mind me asking, how much did this all cost you?

[Qproject]

OK thanks for the info, BUT you forgot to mention one really IMPORTANT thing.

DID IT FIX THE PROBLEM ?

In my particular case, the injector #5 and, more recently #2, were the source of the stumble and then misfire. I use only 93 Shell or Chevron gas, had the fuel filter replaced, all regular cleaning (EGR, Plenum, IACV, TB, etc.), and all up-to-date maintenance done (including new PFR5G-11 plugs, PCV, KS, harness, and O2 sensors).