# Hey everybody, newbie has a random question...



## lrweeks1120 (Oct 12, 2005)

Hello,
Because of some financial situations I decided to to put some money into my 1995 Nissan Altima (instead of investing in a new car) to put it in much better shape. It's in the paint shop right now, woohoo! Anyway, everybody on here seemed really helpful to even the people who aren't so car savvy which is the category I fall under. So that's why I signed up! 

My first question: I'm trying to get my check engine light off, I've gotten the code for the EGR valve and knock sensor. I checked both of them and the EGR valve had a hose that was pretty much shot so I replaced it. I didn't notice anything irregular about the knock sensor. The light stayed off for a few days and then came back on (with the 2 same codes). My car idles pretty rough with a lot of vibration but I thought it was just because of the mileage and age of the car. I started to wonder that if the EGR valve isn't working properly, could that cause the rough idling and vibration and in turn cause the knock sensor to send the code to the computer? Any input on this issues would be helpful. Thanks everybody!

notes: 
Pistons are firing on time with no misses or pinging
No other hoses are leaking, I checked 
There's power to the two sensors
The check engine light came on when I was at a stop sign for a few seconds


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## LONDONDERRY (May 19, 2004)

You probably need to replace the EGR valve. Its a common problem and a very easy fix to do, just make sure you buy a new gasket with it

F


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## Agoudine (Feb 19, 2005)

I suggest www.nissanpartscheap.com
to buy Egr valve. I bot my for $98. Dealership charges over $150 for the same part. It did not help my rough idling,but at least I know it wouldn't cause any problems. Buy gasket in any store - less than $2.


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## gfriedman (Oct 12, 2005)

Agoudine said:


> I suggest www.nissanpartscheap.com
> to buy Egr valve. I bot my for $98. Dealership charges over $150 for the same part. It did not help my rough idling,but at least I know it wouldn't cause any problems. Buy gasket in any store - less than $2.


Most rough idling problems on this car seem to be caused by vacuum leak. See whether your intake manifold gasket is leaking.

Gene


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## lrweeks1120 (Oct 12, 2005)

*Good feedback, it's appreciated*

Thanks for your input everybody! Any other very common problems I should know about? And does anybody have any easy and good suggestions on finding a vacuum leak or is it just one of those tedious and time consuming things? Thanks again guys! This will definately be an educational experience for me! haha


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## jserrano (Oct 27, 2004)

_[Prepare for a brain dump...]_

If your car has over 60,000 miles and you've never serviced the EGR system, then it is probably full of carbon deposits. Too much of it could cause the EGR valve to either stick open (rough idling) or closed (excessive pinging). 

There is an EGR/EVAP solenoid valve which also plays a role with letting a vacuum signal reach the EGR valve and EVAP canister. It is controlled by the ECU.

There is also an EGR temperature sensor atop of the intake manifold which senses the exhaust going through the EGR valve. The ECU uses it to time when to activate the EGR solenoid valve and it also serves as a diagnostic feedback.

Finally, there is an EGR Backpressure Transducer (BPT) that senses exhaust pressure. When the pressure is low (idling/deceleration) it bleeds off the EGR vacuum line to air so the the EGR disactivates. During high exhaust pressure (acceleration/cruising), it lets the EGR/EVAP solenoid valve vacuum signal reach the EGR valve, to operate as normal.

The hose underneath the EGR BPT wraps around to a port located over the throttle body. That brass metallic tubing is known to clog up badly where it meets the cast iron piece. If clogged, the EGR valve won't activate properly. Getting that piece of tubing out requires some chemicals, lubricant, and some serious twisting but it can be done.

The knock sensor (KS) code is totally different and unrelated. Nissan KS sucks and are known to be one of the highest failure item in the car. Internally, they are made of a material called a piezoelectric crystal and the electrodes that connects to it somehow disconnects from the crystal with high temperature. That is why the diagnostic code seems to clear when the engine is cool but will eventually comes back on the first hot engine drive test you make. The KS doesn't set the the CEL but it gets stored in the ECU. The CEL came from the EGR problem.

An intake leak can be identified with a vacuum gauge. When my EGR went bad on me my vacuum was sitting around 16 in. Hg instead of the normal ~21 in. Hg. They're cheap and useful to have around.


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