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

[maxnix]

could it be the KNOCK SENSORS?

weren't these known to be faulty on the older g50's ?

Since turning on my AC adjusts the IDLE.

Knock sensors fail due to heat and age. Same for their harnesses.

IAC valve is active whether AC is on or not, as I understand it. The on and off again drag of the compressor will require it to cycle more often, of course. Why it (and other parts of the intake path) must be clean before diagnosis is attempted. If it's sticking, it will introduce a stumble.

OK, one last time - there are many possible causes for the stumbling. One must start from a known good baseline (clean intake path, TB, IAC & EGR valves and interior manifold tube, air and fuel filter) and proceed systematically to diagnose the problems, provided one does not have supernatural extrasensory perception.

Modified by maxnix at 6:51 AM 8/11/2007

[Qproject]

according to farfetched here:

zer...12366

it was the knock sensors.

[ZMARKUS]

Simple two different causes of the misfire: a lean mixture in the cylinder and a weak spark. Partially improve one defect [for 3 weeks] by cleaning up the injector, just enough spark to begin to work. Until the injector gets back dirty again from the gasolone without BG44k.

Hey Q45tech, I noticed the link in this particular message and was curious were you employed with T3 or just kinda giving a shot out so to speak?

[Qproject]

so did anyone check out this link ?

zer...12366

[ZMARKUS]

I've read the forum that link leads to you speak of and found it quite helpful and interesting. It actually provoked my first attempts to resolve my issue trying ISO-HEET, injector service and BG44K in gas. That forum brings attention to the IAC valve and sometimes I think I should have it along with the EGR cleaned to eliminate those possibilites, but having a P0330 code keeps me looking at replacing the knock sensor 2#. Especially since it seems the successful stories tend to stem from knock sensor replacements.
Modified by totaljett at 10:25 PM 8/19/2007

[ZMARKUS]

Well, guess who finally got a check engine light to go along with this fancy stumbling. Whats that, you give up, me . I scanned it and it the code represents multiple cylinder misfire. Did I mention it stumbles less when I am well below half a tank of gas . The p0330 code is still there although it never activated the check engine light. Could it be knock sensor worsening has caused the misfires to grow to the point of trigger ing the check engine light and sometimes I wonder do I just need a professional intake cleaning.


Modified by totaljett at 12:24 PM 10/25/2007

[96Qowner]

A misfire won't throw a code until it happens so many times in a certain period of time.

Which cylinder(s) misfired? If you can narrow it down, yer in luck. The biggest problem has been no code = no cylinder.

Link to another thread with detailed discussion of Q45 misfires:

y33 idle jerk / hesitation discussion

[ZMARKUS]

A misfire won't throw a code until it happens so many times in a certain period of time.

Which cylinder(s) misfired? If you can narrow it down, yer in luck. The biggest problem has been no code = no cylinder.

Link to another thread with detailed discussion of Q45 misfires:

y33 idle jerk / hesitation discussion

Thats exactly whats happening, looping multiple misfires coming and going instead of the once singles . They've gotten that bad and I expected that CEL to come on eventually. It doesn't say which cylinder when scanned just the p0300 for random multiple cylinder misfire and the p0330 code that was already there but never triggered the CEL. Also still noticing the misfires are cut by 90% when I add a bottle of Techron or BG44K to tank but return after fill up without either addiditive. Maybe the random misfires represent not particularly a bad cylinder, but a culprit like carbon causing misfires in possibly perfectly fine cylinders. This is why I'm considering a professional BG induction service. Then again it could be a knock sensor worsening causing this, but the fuel addiditives almost eliminating it altogether suggest fuel related. Then again maybe.............. ah dammit .

[ZMARKUS]

Since the weather has gotten cold my stumbling has minimized greatly. Now for the last 5 days we have had unusual warm weather ( high 70's reaching 80) and the stumbling is often again. Anyone have a take on this and could carbon in the induction system cause more symptoms in warmer temperatures than cold. I ask this because my first attempt at resolving this will be the BG induction service.

[bullittandy]

Thats exactly whats happening, looping multiple misfires coming and going instead of the once singles . They've gotten that bad and I expected that CEL to come on eventually. It doesn't say which cylinder when scanned just the p0300 for random multiple cylinder misfire and the p0330 code that was already there but never triggered the CEL. Also still noticing the misfires are cut by 90% when I add a bottle of Techron or BG44K to tank but return after fill up without either addiditive. Maybe the random misfires represent not particularly a bad cylinder, but a culprit like carbon causing misfires in possibly perfectly fine cylinders. This is why I'm considering a professional BG induction service. Then again it could be a knock sensor worsening causing this, but the fuel addiditives almost eliminating it altogether suggest fuel related. Then again maybe.............. ah dammit .

"Q45tech

Simple two different causes of the misfire: a lean mixture in the cylinder and a weak spark. Partially improve one defect [for 3 weeks] by cleaning up the injector, just enough spark to begin to work. Until the injector gets back dirty again from the gasolone without BG44k."

I like the failing coil that's helped along by a perfectly clean combustion chamber.

[bullittandy]

I had a bad coil in my wife's Volvo V70, exact same symptoms, stumble at idle but would eventually smooth out with some throttle-though not perfect.

I found the bad coil by pulling the connectors on each coil until the idle stumble didn't change. In other words, every time I pulled disconnected a good coil, I then created two misfiring cylinders, but pulling the connector on the bad coil did nothing because it was already dead-kind of like pulling plug wires on a distributor cap.

Now, the V70 is an inline 5 cylinder with the coils laid nice and pretty under a small plastic cover as compared to the Q which has a bunch of crap in the way. But if the stumble is at all reliable the above method should work.

[Mint Q45A]

Here are my two cents (based on something I remember reading somewhere else)....

Check (clean and tighten) the connections going from the ECM to each of the two Power Transistors, and from the Power Transistors to the Ignition Coils.On the G50 there are two Power Transistors (one for each bank), located on top of the valve/coils covers. The connector with 5 pins is the one from the ECM; the one the other side, has 4 pins and feeds each one of the four coil packs on that side.

This thread has a picture posted by Goody94q45 that illustrates how to do something similar, but in this case it is for the MAF connector on a G50. I assume the same principle could apply to the Power Transistors

zerothread/297840

I know you are referring to a different car, but is worth trying....specially considering that some of your error messges have pointed to the coils...
Modified by Mint Q45A at 12:34 PM 12/15/2007

[Q45tech]

Inside the ignitor assembly there ar FOUR TRANSISTORS [actually 8 in darlington configuration] plus 4 zener diodes and assorted resistors.

The low voltage from ecu [another transistor] controls the conductance of the ignitor transistors, much like how a relay allows a small current/voltage to control a big current voltage. [headlights. fuel pump, fans , etc].

Afterall to saturate each coil takes more than 10 amperes and this is repeated every 2 rpms......19 million times per 100,000 miles

Never seen a bad/corroded connector on ignitor failing to trigger transistor inside ignitor. There is an excess and the drive current is miniscule.

Comments don't apply to flooded or submursed cars sloppy rebuilt.

An almost NASA quality system in 90-93 Q, which declined in robustness as the designs progressed: > 94-95> 96 >97-01. saving dollars here and there allow the prices to stay ~~ $50k.

"This thread has got me thinking. Why haven't Maxnix or Q45tech solved this problem yet?"

We have solved this every week or month since the problems started on 97 Q and I30/I35/M45. We give a 12month replaced parts warranty and 12 months labor warranty on the parts replaced.

The usual problem is the customer doesn't want to spend the $500- $1,500 it might cost................we charge them $85-$170 for diagnosis and wait until they sell some blood.

[ZMARKUS]

Hey.....anybody here? Well, I just wanted to say the problems of this thread were finally resolved. Although I did replace all ignition coils, something was done before that and eliminated the symptoms. An EGR carbon cleaning service was done. Got all my passages cleaned out and the problems were no more . I still changed the coils shortly after because it was due anyway. I feel the EGR passages became more and more clogged overtime as the stumble became worse overtime. I had a induction cleaning done but didn't know of EGR system cleaning at that time. The support was greatly appreciated.

[maxnix]

Thanks for commenting your result, totaljett.

Same thing happened to me when I replaced the defective coilpack. A little while later, very slight hiccup would occur on a hot day at idle, no code.

Cleaned everything under the plenum, especially the EGR tube in the plenum which was coked (how was yours?), EGR and IAC valves and now it idles butter smooth.

[ZMARKUS]

Thanks for commenting your result, totaljett.

Same thing happened to me when I replaced the defective coilpack. A little while later, very slight hiccup would occur on a hot day at idle, no code.

Cleaned everything under the plenum, especially the EGR tube in the plenum which was coked (how was yours?), EGR and IAC valves and now it idles butter smooth.

When the guy was performing the EGR service on my vehicle, he stepped out the bay from time to time because of the serious carbon smoke coming out. It was filthy and like I said an Induction and fuel injection service was done some time back to remedy the problem but it was the EGR passages needing cleaning all the time. My overlooking cleaning that area caused me to live with the issue much longer than I had to. It's now as smooth as a Chicago Pimp and powerful as a Middle Eastern Dictator. Infiniti Parts Usa prices are incredible by the way, that Infiniti Dealerships should be egged. All 8 OEM coils were $660.00 shipped.

[maxnix]

Man, I just used a Dremel with a steel brush and copious quantities of Berryman Chem Tool.
Modified by maxnix at 8:59 AM 4/8/2009

[Ludeaem]

i used seafoam

[maxnix]

i used seafoam

How did you break out the carbon coke?

[Ludeaem]

How did you break out the carbon coke?

Not sure if i did or not just saying it did burn off a lot of carbon evidence of all the smoke. I'll do it again soon

[maxnix]

I doubt if any amount of solvent, especially kerosene and paraffin based like Seafoam, will dislodge the coked up carbon. The solvent introduced into a vacuum line is not even getting into that tube.

[miata007]

Hi is cleaning the EGR valve be sufficient?

I am hoping I don't have to remove the plenum. What kind of effort will that involve. I've read is a pain for 1st gen Q45.

007

[maxnix]

Can't get the EGR tube out without removing the plenum.

The inside of the tube is where all the coke is. The VH41DE plenum is a piece of cake compared to the VH45DE. And once you are in there, you will see why it is a good thing.

[ZMARKUS]

Speaking of EGR , mine has triggered a p0402 CEL ( overflow) the other day. So today I removed it and sprayed it out with carbon cleaner. Don't know how much that helped because there was very little if I recall any dripping from the valve. Unlike my Lincoln Ls which was making chocolate milk . Not as easy to get to as the Lincoln as well. So, I'll see if the code comes back and if so the EGR valve probably needs replacing.

[maxnix]

So, I'll see if the code comes back and if so the EGR valve probably needs replacing.

Better to clean it and the plenum tube downstream in particular.

[slybydesignq45t]

This was an interesting read. Makes me wonder, if these issues led to the depreciation in the Q45's compared to other makes and models of the same vintage. I know a lot of the Q's depreciation was do to the original advertising, but these other issues may have contributed to its depreciation after the initial launch.