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sprinkles08
sprinkles08, ASE Certified Technician
Category: Infiniti
Satisfied Customers: 21586
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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1999 qx4, is there a constant vacuum of the EGR valve when

Customer Question

1999 qx4, is there a constant vacuum of the EGR valve when the throttle is applied? or is there only vacuum when the throttle is first pressed?? also when i apply vacuum to the valve when the car is at idle should the car kill? it just chuggs but doesnt
completely kill.
Submitted: 1 year ago.
Category: Infiniti
Expert:  sprinkles08 replied 1 year ago.

Hello and welcome to JustAnswer!

There will be constant vacuum to the EGR solenoid when the engine is running. The solenoid is turned on and off by the engine controller to keep the EGR valve closed at idle, where the engine can't really tolerate EGR flow.

Some engines will die if an EGR valve is forced open at idle, some will just run poorly. If it does cause the engine to run poorly then it's flowing. If you aren't setting a code for lack of EGR flow there isn't a reason to be concerned with it not dying, if it runs poorly then the valve is able to open.

Customer: replied 1 year ago.
Okay so here's the thing. There is no vacuum going to the solenoid unless the gas is pressed and if you keep holding the gas the vacuum goes away. Does this mean I have a vacuum leak somewhere? Or what does this mean? I'm getting a po430 code for bank 2 where the egr valve connects to the exaust could these be related
Expert:  sprinkles08 replied 1 year ago.

There's no reason to be concerned with the EGR system if you aren't setting an EGR code or having driveability concerns from the valve leaking when it should be closed. P0430 indicates an efficiency failure of the bank 2 catalytic converter, this can only be caused by the converter itself, a lazy upstream oxygen sensor, or an exhaust leak upstream of the converter drawing oxygen into the exhaust stream.

Customer: replied 1 year ago.
Well heres another thing i should bring up, the car misfires when you rev it a low rpm. when you give it gas the rpm will not stay steady. which maybe sounds like its not burning the oxygen??? and because i dont think this EGR valve is working properly i think it may be causing misfires.
Expert:  sprinkles08 replied 1 year ago.

If you suspect the EGR valve is leaking then you can block the tube temporarily for testing and see if it runs better, but not until after the catalytic converter issue is repaired. A restricted converter will cause misfiring and can also blow the EGR valve open from backpressure.

Customer: replied 1 year ago.
How do you check each Catt with an infected thermometer
Customer: replied 1 year ago.
Infered
Expert:  sprinkles08 replied 1 year ago.

A backpressure gauge would need to be installed in the upstream oxygen sensor location on that bank to see if the converter is restricted if that's what you were wanting to check.

Customer: replied 1 year ago.
There is a plastic screw In The back of the manifold what does it do?
Expert:  sprinkles08 replied 1 year ago.

In the intake? Can you upload a picture of what you're seeing?

Customer: replied 1 year ago.
It's in a tight place to get a picture of. I read it is the idle screw. I ended up replacing the bad cat. Turns out it was broken inside. After replacing the cat the emissions are still to high but better. I wonder because I was messing with the screw and the throttle position screw. Is there a trick to adjusting them both? I want it to pass smog here in California. My nox and HC are too high
Customer: replied 1 year ago.
In other words should I raist the idle screw and lower the flap or lower the idle screw and increase the flap
Expert:  sprinkles08 replied 1 year ago.

Changing idle speed isn't going to correct emissions issues. Is idle speed correct?

Where did the replacement converter come from?

Customer: replied 1 year ago.
I got the converter from autozone. $200 with $50 mail in rebate. Not a bad price. However I am getting no vaccuum on any of the small vacuum lines which concerned me and makes me think egr is not working properly
Expert:  sprinkles08 replied 1 year ago.

An aftermarket converter is sometimes enough to keep the engine light off for a couple months but it's not going to perform as a factory replacement would.

Are any fault codes currently setting?

Customer: replied 1 year ago.
no there is no faults, however when i first picked up the car. it had a cat code for both sides. I swapped out all the o2 sensors and the bank 1 code went away. i would assume since the left was fried the right is probably on its way out. i noticed there was a vacuum line that ran from the manifold to some sort of electronic switch which i by passed and now there is constant vacuum to the solenoid and the car seems to be running okay.. i will see the results on a pretest tomorrow, if it still fails i will probably break down and buy another catt.
Expert:  sprinkles08 replied 1 year ago.

Can you explain more abut or upload a picture of what you bypassed?

Customer: replied 1 year ago.
it kind of looks like this
Expert:  sprinkles08 replied 1 year ago.

Did you remove that and run the vacuum lines together?

Customer: replied 1 year ago.
I put one vacuum line
Expert:  sprinkles08 replied 1 year ago.

That's at least part of the issue, you're constantly drawing out of the evap system with full manifold vacuum. The solenoid is going to need to be replaced.