99 QX4 - brake applied and tach surges

[99.5 qx4]

My qx4 is acting weird. When driving at 65-70 mph (no cruise) and the brake is applied, the tach surges from 2500 to 3500 before settling back. Took car to local mechanic, no codes (other than stored O2's with no check light). Car has not had onboard computer upgrades since I've owned it (2 years). They checked mechanical and can find no apparent cause. They suggest taking car to dealer to have all computer upgrades (~$175). They suspect it may be computer related since the throttle is controlled electronically. Know of any specific TSB's or have any suggestions?

I searched through the forums looking for tach surge, brake and tach surge and found nothing related

[elwesso]

So it ONLY does it when braking, or does it do it under general deceleration???

Seems weird, but i really doubt the dealer would help you much.... Let me think about this.

[99.5 qx4]

It is only when the brake is applied and it happens at both lower speeds 35-45 up to higher highway speed. It is as if you get a burst of gas. Not really surging the car forward but just revving the engine.

[Q451990]

On the Q45 there's a check valve in the vacuum line that goes to the brake booster. If the QX4 has this, and something was weird with it, could that cause an issue - e.g. pushing a surge of air into the intake? Just a thought...

Heath

[elwesso]

great thought heath!!!!! id check it!

[99.5 qx4]

Sounds like a possibility. How do I check this and/or replace it? Is it something that will be obvious when I look at the line to the brake booster?

[Q451990]

Here's a page from the FSM for a 99 QX4. I think this is a long shot - but worth checking.

Heath

[99.5 qx4]

Looked over this whole assembly and no apparent problem with the hoses. Removed the check valve and blew air through it. It seemed to have a 'catch' initially. It may have been sticking. Did not have vacuum tool to check it so reinstalled and it is much improved. Still does it but not as much. Ordered replacement and will see if problem goes away completely. It will be a few days. I'll post again after new part installed.

[elwesso]

how much was the new check valve?

[99.5 qx4]

It was $30 (through Nissan dealer p/n 47478-51E00 --$42 @ Inifiniti) -- Couldn't cross reference at any local parts store, so stuck with dealer. Do you know of a cheaper place? Also decided to replace the retaining clip (plastic broke on removal) at about $16.

[elwesso]

Thats not too bad... $22 from Joe at http://www.infinitipartsusa.com by the time you factor in shipping ($5 minimum charge) not really saving much.

[Q451990]

Please let us know how it all turns out... even if you are from Arkansas That was a nice butt whooping you guys put on us earlier tonight. (Ignore my rambling if you aren't a football fan)

Heath

[99.5 qx4]

Go HOGS!! Wooo Pig Sooie!

[99.5 qx4]

Sorry this took so long but wanted to report that replacing the check valve DID fix this problem! You're a WIZARD!!! Thanks so much for all of the help!

[elwesso]

Excellent, glad it was very simple!!!

This forum=+1 point

[Q451990]

Sorry this took so long but wanted to report that replacing the check valve DID fix this problem! You're a WIZARD!!! Thanks so much for all of the help!

Talk about a long shot working out... That's great news!

Heath