Revving on its own

[kawasakirob]

I drive a 2001 Hyundai Accent with 257k miles. It started revving on its own just recently. It has a manual transmission and has been running just fine until now.

I've been told to check the airbox, the vacuum hose connecting to the airbox (for cracks) and the spark plugs. I've also been told to add some additives to the fuel in order to clean the injectors.

What do you guys think?

[Zach929rr]

Checking for vacuum leaks and cleaning the MAP/MAF is a good start.

My explorer would do this when the MAF got dirty thanks to the head ventilation dumping into the intake tube pre-MAF.

[asp_125]

Need more info. Revs go up while idling? Revs drop (like it wants to stall)? While in gear? While under load? Clutch slippage?

I'd suspect vacuum leak, too.

[kawasakirob]

Need more info. Revs go up while idling? Revs drop (like it wants to stall)? While in gear? While under load? Clutch slippage?

I'd suspect vacuum leak, too.

All the time. Idling, clutch in or out.


Checking for vacuum leaks and cleaning the MAP/MAF is a good start.

My explorer would do this when the MAF got dirty thanks to the head ventilation dumping into the intake tube pre-MAF.

What's the MAF?

[Zach929rr]

Mass Airflow Sensor.

http://img40.imageshack.us/img40/8223/accent.jpg

[madvlad]

When you drive it does it act up at all?

[kawasakirob]

No not really. Just wants to keep revving

[jcj81]

Its sounds like a vacuum leak issue, but first make sure throttle isn't sticking. If it is a vacuum leak it usually would have to be a large leak to cause engine to rev, are you able to hear a leak, air being sucked in? Check the hose coming off the brake booster thats usually the largest vacuum hose. What rpm does it idle at?

It could also be the idle control valve possibly sticking with that mileage carbon could cause it to stick.

[kawasakirob]

At idle: 500-3k
But if I'm driving and push in the clutch at 3k it'll rev higher.

Also getting on/off the gas is pretty jerky. I put some BG400k in the tank to see if it improves while I do some driving tomorrow. I will check for air in the vacuum hose and get back with you guys.

[3point5]

OP, throw a youtube video up...

[matt2778]

Does it hunt or just rev up?

[madvlad]

Its sounds like a vacuum leak issue, but first make sure throttle isn't sticking. If it is a vacuum leak it usually would have to be a large leak to cause engine to rev, are you able to hear a leak, air being sucked in? Check the hose coming off the brake booster thats usually the largest vacuum hose. What rpm does it idle at?

It could also be the idle control valve possibly sticking with that mileage carbon could cause it to stick.

I'm thinking the idle control valve but then if the revs differ since he posted 500 to 3k that's kind of a huge jump, sounds more to me like it's idle surging.

[neh]

Disconnect the MAF sensor and see what it does. It should go to limp mode. If it levels out, then carefully clean the connector and very, very carefully clean the MAF sensor.

[Kim-n-Dean]

Throttle Position Sensor.