2007 Fit Sport, 150K

What's wrong: A few seconds after I start my Fit, it begins to rev on its own, only a few hundred RPMs up and back down, about once every second or so. This revving continues while driving, creating a mild "bucking" sensation while driving around town (highways or residential roads). There is no hesitation or stutter in the engine (as I've found previously when I needed either a valve adjustment or new coil packs), and having the A/C on or off doesn't help or hurt. It makes the car very hard to drive as it doesn't have the proper power to accelerate to highway speeds in a reasonable amount of time.

Things I've tried: New coil packs, new O2 sensor, valve adjustment (just in case), half can of Seafoam at last fill up, and new plugs. I also took the airbox back off because it looked like there was an issue with the connection of the rubber insert that goes between the airbox and the throttle body. I also double checked the electrical plugs and nuts and bolts to make sure I didn't leave anything unplugged or loose when putting it back together.

That said, I'm at a loss. I have no clue what could be wrong. I need to get a new air filter, but the one that's installed isn't THAT bad. What could the problem be???

 

Did you check for loose hose, cracked fitting or other source of vacuum leak?

 

I checked all of my hoses, but didn't spot anything out of the ordinary. I'm hoping somebody else has experienced this same problem and can point to a likely culprit instead of

 

Clogged Fuel filter can cause that behavior...

 

I understand that the Fit has an in-tank fuel filter. I'm not necessarily ruling that out, but I'm pretty sure that's the last thing I will try. Thanks though!

 

welcome to SLEV vehicles.. arg.

on the SLEV BMW's you have to swap out the whole freeking fuel tank for about 2200 bucks for a couple years.. UGLY... Since the pump was good for about 80K..

 

I'd clean the throttle body and do the Idle Learn Procedure. That costs nothing but time, and it's a good first attempt.

Dirt in the TB/butterfly confuses the ECU. Then, it starts to sulk. LOL

It THINKS the butterfly is closed, but the dirt holds it open...and the ECU tries to compensate.

 

Any check engine codes?
Have you accidentally touched a throttle valve when doing valve clearance check?
Possible vacuum leak at brake booster hose, intake plenum, stuck open PCV valve or defective gas pedal position sensor (not fully returns to idle setting when gas pedal is released) I am not listing EGR valve or purge valve stuck open because this will typically set a code. the intake hose cracks will not affect this engine much. If it will be Ford car I would blame throttle valve actuator (bad gears) or defective MAP sensor.
If you can hook up a scanner read all PID (full data set when engine is misbehaving) and post it here.
Also try moving all electrical connections on sensors.

 

Codes thrown:
P2252
P0134

 

Another aspect I noticed the other day was that the engine ran pretty hot. I took it in to AutoZone and on the 10 minute drive (after disconnecting the battery yesterday), the CEL never came on, but the surging while driving continued. I sprayed some carb cleaner around to check for any vacuum leaks while at AutoZone, but found nothing. I then decided to try again at home since the CEL never lit up. Lo and behold, on the way home, the light came on and the car actually kind of drove normally without bucking as I turned around to head back to AutoZone. The surging RPMs came back right about the time I pulled into AZ. I got the codes read and they came back as P0134 and P2252. I'm not entirely sure where all I need to spray to check for vacuum leaks, so anybody with a picture would be much appreciated. Keep the ideas coming.

 

Both codes are pointing to the Air-fuel sensor (proper name for O2 sensor used on Fit). First code says it is inactive (not producing current) [Note: the a/f sensor changes amount of current flow through its circuit when mixture changes as opposed of O2 sensor that changes voltages). Did you use Honda sensor or aftermarket one?
Similar situation discussed here: getting a p2252 check engine light. replaced both o2 sensors

 

I used this O2 Sensor:

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

 

I would not trust aftermarket parts for Japanese cars unless they are 15 years old or older.
This is the part number from Honda parts cheap (it costs $219) 36531-RME-A52 SENSOR

 

That is a sign of vacuum leak. Try checking pcv valve. It might be stuck open. To check this, I would pinch on the rubber hose running from pcv valve to the top middle of intake manifold(you need to take off the manifold plastic cover). I highly suspect that.

 

This is a downstream sensor

 

Vacuum leak will not cause these symptoms on 07-08 US Fit which is using MAP sensor; it may cause higher than usual idle but not performance loss under load