|
|
08 Nissan Sentra engine revs up without giving it gas
|
|
|
| |
|
|
gregg729
New User
Jun 21, 2014, 9:29 AM
Post #1 of 9
(1566 views)
|
|
08 Nissan Sentra engine revs up without giving it gas
|
Sign In
|
|
Hello everyone!
So I thought I'd ask all of you here about my latest car issue. I don't really have any experience working on cars but I am an electronics mechanic on submarines so who know, maybe I can take care of it myself if I get pointed in the right direction.
About my car:
- 2008 Nissan Sentra
- Not sure the engine size, it's the base model size, not souped up or anything
- Just shy of 81k miles
- Automatic transmission
This started happening about 3 days ago. I'll be driving along, go up a hill. Then when I go down the other side I'll lay off the gas and coast. And what happens is the engine will wind down to its normal idling speed and when it hits that RPM, it will give it more gas. The engine and tach will rev up to about 3k, stay there for up to 10 seconds, then wind back down to normal idle speed. The clutch is apparently still engaged because the car doesn't try to speed up, just the engine.
This is even more observable when it's in cruise control.
I've used my foot to pull the gas pedal back, and that is not the issue. So would that tell me it's something about the throttle valve? (Not sure of my terminology. By throttle valve, I mean whatever valve-type-thing opens up to give it more gas.)
Anyone know what the issue is, and what needs to be done to fix it? What skill level do you think one would need to tackle this? I'm decent with my hands and am mechanically knowledgeable but I really know nothing about what's going on underneath the hood.
And lastly, any ballpark idea of how much I should expect to pay to get this fixed at a garage?
Thanks, Gregg
(This post was edited by gregg729 on Jun 21, 2014, 9:34 AM)
|
|
| |
|
|
Hammer Time
Ultimate Carjunky
/ Moderator
Jun 21, 2014, 9:44 AM
Post #2 of 9
(1555 views)
|
|
Re: 08 Nissan Sentra engine revs up without giving it gas
|
Sign In
|
|
I can't tell you for sure for this specific model but this may be completely normal, especially if you are not seeing any check engine light. This may be programmed into the operating system for emissions reasons.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
|
|
| |
|
|
Hammer Time
Ultimate Carjunky
/ Moderator
Jun 21, 2014, 9:58 AM
Post #4 of 9
(1549 views)
|
|
Re: 08 Nissan Sentra engine revs up without giving it gas
|
Sign In
|
|
It's going to be hard for anyone to determine without examining the car to see what is going on. It may have a decel valve that is messing up if it even has one or an IAC not working smoothly. It really needs to be checked out by a professional to get some direction.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
|
|
| |
|
|
kev2
Veteran
Jun 21, 2014, 10:01 AM
Post #5 of 9
(1544 views)
|
|
Re: 08 Nissan Sentra engine revs up without giving it gas
|
Sign In
|
|
to add to HT's reply-
Take advantage of the FREE scans available at autozone, advance, Orielys - auto parts stores- yes even if the CEL light out.
It is an automatic transmission ? so there is NO clutch per say.
You were close - the term is THROTTLE BODY- that meters air to engine you were close with throttle valve.
Suggestions
Look at the transmission fluid
Take for a free scan... its FREE
that should take a sailor a day - or two :)
I will look into this AS I hope it is not a CVT trans,
Kevin
USAF retired
|
|
| |
|
|
Discretesignals
Ultimate Carjunky
/ Moderator
Jun 21, 2014, 10:09 AM
Post #6 of 9
(1540 views)
|
|
Re: 08 Nissan Sentra engine revs up without giving it gas
|
Sign In
|
|
We don't have steep hills where I live, but Nissan may have programmed the engine computer to add engine braking when the vehicle is going down hill and accelerating when the driver isn't touching the brake or gas for a period of time. It being more apparent with cruise control turned on would seem to prove that point sense the cruise control system is trying to maintain a set speed.
Best advise is to drive another Nissan the same year, engine, and transmission to see if the problem is actually normal operation.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jun 21, 2014, 10:10 AM)
|
|
| |
|
|
gregg729
New User
Jun 22, 2014, 10:15 AM
Post #7 of 9
(1491 views)
|
|
Re: 08 Nissan Sentra engine revs up without giving it gas
|
Sign In
|
|
to add to HT's reply-
Take advantage of the FREE scans available at autozone, advance, Orielys - auto parts stores- yes even if the CEL light out.
It is an automatic transmission ? so there is NO clutch per say.
You were close - the term is THROTTLE BODY- that meters air to engine you were close with throttle valve.
Suggestions
Look at the transmission fluid
Take for a free scan... its FREE
that should take a sailor a day - or two :)
I will look into this AS I hope it is not a CVT trans,
Kevin
USAF retired
I would love for it to be a CVT issue, as that's still under warranty.
Anyway, update:
I had it scanned at VIP, there were no error codes found.
But the guy at VIP and another dude who seems to be knowledgeable both say that even without any error codes, it still could be one of the throttle body - the air intake sensor, the throttle position sensor, and I forget the third one right now. And one of the guys said a faulty wheel sensor might be sending an erroneous wheel RPM signal to the computer, therefore causing the problem - is this possible?
EDIT: And I was also told by one of them that he was "reasonably sure" it was a multi-port vs. single port throttle body, if that's relevant at all....
So anyhow, I was also told that these sensors are tested with ohmmeters. Ha! That's right up my alley, I could use a multimeter blindfolded. So testing the sensors is something I can do, I think. Disconnect them - if it's giving me any number for a reading the sensor's good, and if it's an open or a short I found the bad sensor and most likely the problem - correct?
Am I on the right track? If so, a few questions come to mind. Is there a free online repair manual anywhere I can look at? Anything I need to bear in mind while disconnecting and testing, or any other considerations at all I need to be aware of?
Thanks so much!
(This post was edited by gregg729 on Jun 22, 2014, 10:17 AM)
|
|
| |
|
|
Discretesignals
Ultimate Carjunky
/ Moderator
Jun 22, 2014, 10:28 AM
Post #8 of 9
(1487 views)
|
|
Re: 08 Nissan Sentra engine revs up without giving it gas
|
Sign In
|
|
I can tell you right now that if there was a problem with a sensor, especially ETC related, you would be seeing the check engine light and possible throttle control limiting going on.
Ohm meters are good for checking continuity, but when checking sensor operation you want to use a volt meter or lab scope. You want to test the sensor or actuator under operating conditions.
I personally still think that you should test drive another Nissan the same as yours to see if the problem is actually a problem or not.
Once you find out it is an actual problem, time for diagnostics.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jun 22, 2014, 10:30 AM)
|
|
| |
|
|
kev2
Veteran
Jun 22, 2014, 10:47 AM
Post #9 of 9
(1483 views)
|
|
Re: 08 Nissan Sentra engine revs up without giving it gas
|
Sign In
|
|
I show this (tech data) as a CVT trans, one of 2 models MR20DE or MR25DE.
Unfortunately I never worked on them, CVT's are not very common- Trying to translate your issue to the list of symptoms
and likely repairs is difficult. It has (3days ago) changed its operation, the engine speed is independent -hunting- as the vehicle speed remains constant... only thing I could see close is engine braking issue..
There are a number of codes related to CVTs manufacturers specific & U series etc BUT most scanners* will not read them.
If there a warranty -I would let Nissan look at it...
*requires a professional all module capability
|
|
| |
|
Auto Repair Home
SEARCH
WHO'S 
LOG 
2011 Dodge Nitro OBD scanner seems to drain battery in 10-20 minutes
Grounding Cable, 2017 Jeep Renegade Trailhawk
equipment
Howdy
