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Brendan Block
Brendan Block, Technician
Category: Car
Satisfied Customers: 259
Experience:  BMW Technician specializing in engine conversions, braking upgrades and race car prep.
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hello i have a 03 infiniti g35 sedan and the car shakes at

Resolved Question:

hello i have a 03 infiniti g35 sedan and the car shakes at idle. there is no cel and drive fine only a slight hesitation when u hit the gas. i have change plugs, coils, injectors and fuelpump and the upstream 02 sensor but still shakes..the muffler is black and makes a poping sound like a backfire at idle..
Submitted: 1 year ago.
Category: Car
Expert:  Brendan Block replied 1 year ago.

Fidhle007 :

Hi there!

Fidhle007 :

My name is XXXXX XXXXX I can help you today!

Fidhle007 :

What do you have for diagnostic equipment?

Customer:

right now dont have any but i know enough to explain and help u out

Fidhle007 :

Ok, one more question: does this happen all the time or is it more prevalent when the car warms up for a bit?

Customer:

all the time but it shakes more when warm up..

Fidhle007 :

Ok, so off a cold start it will be better, right?

Customer:

yes on a cold start no shake at first but as it warms up it starts

Fidhle007 :

Ok, good

Fidhle007 :

This is a classic case of a failed ECU coolant temp sensor

Fidhle007 :

The sensor is no longer reading the increasing engine temp and so the ECU is assuming the car is still cold and is supplying air/fuel in a much more rich mixture than it would on a hot engine

Fidhle007 :

Once you get on the throttle, the o2 sensor should be handling most of the mixture but I would be willing to bet it's still running rich

Customer:

the car is running rich, u can smell it and it make the poping sound like a backfire

Customer:

why not the mass air flow

Fidhle007 :

Exactly :-)

Fidhle007 :

Because the temp sensor is $30

Fidhle007 :

MAF is my second guess but I've had this same situation on two very different cars recently in my own shop

Fidhle007 :

The temp sensor is a cheap and easy fix so if it winds up being an MAF you're only out $30 and you have a new temp sensor!

Customer:

ok i see what ur saying..could bad 02 sensor cause that too

Fidhle007 :

Not likely, if the MAF or O2 sensors were bad, chances are you'd see issues all the time

Fidhle007 :

It would cough and hesitate under load as well

Fidhle007 :

You say it hesitates but once it goes, it's ok?

Customer:

yes..driving is ok no problem but once stop or at idle u feel the shake and hear the poping noise from the muffler

Fidhle007 :

Ok, good. I wanted to make sure I understood

Fidhle007 :

I would definitely replace the temperature sensor, the worst it can do is not fix the issue but I would be very surprised if it didn't!

Fidhle007 :

After that your next shot is going to be the MAF as it's the only other part that can cause the same symptoms. I think you would notice them over the whole rev range if it was the MAF though, the fact that it's just idle is what screams "temp sensor" to me

Customer:

ok so what i did tonight was start the car after it was sitting all day, it hesitated and did not start on the first try, after it started i waited a while the unplug the maf the car stall a bit but did not cut off and the shake got better the cel came on and the slip and vdc light but still making the poping sound..plug back the maf no difference and when i unplug it again nothing

Fidhle007 :

When you unplug the MAF, the car reverts to a "Safety Mode" where it's running off a set a preprogrammed parameters

Fidhle007 :

These parameters are not good enough for everyday driving as the ECU has no realtime monitoring of the engine states but it's enough to limp you home

Fidhle007 :

Go get yourself a temp sensor and see what it does! If I remember correctly it's a blue connector on the water pipe on the back of the passenger head.

Fidhle007 :

It's been awhile since I've been under the hood of a G35 though so you'll have to bear with my vague description

Fidhle007 :

sorry!

Customer:

lol...

Customer:

so why no cel for coolant temp sensor

Fidhle007 :

Because it's just a resistor

Fidhle007 :

If there was a broken wire, sure you'd have a CEL or at least a code stored

Fidhle007 :

You may have a code that doesn't throw a light "Coolant temp implausible" or something like that

Customer:

and why safe mode the car did not shake as much cause the engine would shake but after i unplug the maf it was not shaking

Fidhle007 :

But generally it's just a slow breakdown of the resistor internally and eventually it won't change as much as the temp changes

Fidhle007 :

Because the safe mode is just a stock program that is ignoring the sensors, or at least a lot of them

Customer:

so that bad sensor is causing the poping sound from the muffler and running rich

Fidhle007 :

Exactly

Customer:

ur the first person that said change the coolant sensor

Customer:

what happen if that dont work whats my next step..

Fidhle007 :

The MAF is the next step

Fidhle007 :

it sounds like you've covered the rest of the bases already!

Customer:

i have change almost everything...why was that ur first choice for the problem instead of the maf or 02 sensor

Fidhle007 :

Because I JUST had this same issue with an M3 a few weeks ago

Fidhle007 :

same deal, tried EVERYTHING and in the end it was a $30 sensor

Fidhle007 :

It was an engine rebuild but somehow the new sensor was bad

Customer:

i really hope that it and not the maf..cause thats 500..

Fidhle007 :

Exactly!

Fidhle007 :

I think you'll be pleasantly surprised

Customer:

i have one more question

Fidhle007 :

Sure

Fidhle007 :

and then I'm going to be

Fidhle007 :

lol

Fidhle007 :

:-)

Fidhle007 :

*bed

Customer:

when i start my car tonight it hesitated and did not start on the first try and started on the second try but i head a whinning noise could that be the starter..

Fidhle007 :

Hmm, like after it fired up there was a starter noise?

Customer:

yes like right after it started for a few sec..like it when hand in hand

Fidhle007 :

That could be the starter solenoid sticking

Fidhle007 :

Unfortunately the only fix for that is a new starter

Fidhle007 :

I'd say leave it be until it happens every time and then plan for it.

Customer:

ok thanks, XXXXX XXXXX be very helpful..i will keep u posted on my problem..

Fidhle007 :

Thanks!

Fidhle007 :

Good luck, please leave me a positive rating!

Customer:

sure no problem.. i will contact u direct with any problem i have..

Fidhle007 :

Perfect. Thanks!

Brendan Block, Technician
Category: Car
Satisfied Customers: 259
Experience: BMW Technician specializing in engine conversions, braking upgrades and race car prep.
Brendan Block and 16 other Car Specialists are ready to help you

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