Car revving up on its own

[Gold_cg6_pnw]

So for all you enthusiasts, I recently joined this forum, but I got a huge question. Why would my car rev up to 4000rpm and just sit there and bounce? I just rebuilt my engine and it threw three codes. MAP P0108, TPS P0122, and VTEC P1259. What's the deal?

 

[Accordx]

Well at 4K rpms is where vtec would kick, so there's definitely an issue there. Sorry I can't be of any more help.

 

[Gold_cg6_pnw]

Yeah which is why I'm scratching my head over here. I had a buddy say check my wiring but all that clears inspection. He said maybe unplug the ecu and plug it back in and that might clear the issue, but I haven't found where it is yet

 

[Nam1911a1]

Undoing the battery for about 15 minutes or more will reset the ecu also.

 

[Gold_cg6_pnw]

Not that it means much but I replaced my TPS sensor

 

[lothian]

...it threw three codes. MAP P0108, TPS P0122, and VTEC P1259

the presence of DTC's is interesting. it's not unusual to get those three DTC's in combination. (for example, they can result from the throttle position sensor (TPS) being "stuck" due to extreme and/or sustained low ambient temps. there are other causes. however, interestingly if any or all of the underlying causes disappear, those the ECU clears those three DTC's on its own. regardless of any of that, my hunch is that the source of the codes is the TPS, particularly since you claim to have replaced the thing. for instance, it may need calibration. there are plenty of good videos on YouTube that detail the process of t'shooting and calibrating the TPS.

...rev up to 4000rpm and just sit there and bounce?

i'm confused by your contradictory phrasing "sit there [at 4000rpm] and bounce", which are mutually exclusive conditions. is the engine idle "sitting there" at 4000 RPM? ...or, does it "bounce" between high and low RPM?

if the former, sustained high idle has a few causes, but your focus should be on the TPS--specifically the position of the TPS.

if the latter, this condition is called "idle hunting" (the phenomenon is known by different aliases), though its worth noting that idle hunting caused by the IACV usually does not throw any DTC's. there are plenty of good videos on YouTube that detail the process of t'shooting idle hunting. one possible source of idle hunting is an issue with the air intake control valve (IACV). there are there are plenty of good videos on YouTube that detail the process of t'shooting the IACV. idle hunting can occur after jostling the throttle body. the throttle body is warmed by engine coolant which enters into and flows through the IACV. if the coolant lines to the IACV are removed for any reason, the Honda service manual recommends performing an air purge procedure on the coolant system as the last step in the job. there are plenty of good videos on YouTube that detail the air purge procedure process.

 

[Rusty Accord]

Try swapping the plugs from the MAP sensor and TPS sensor. You mentioned you had it apart, so it's possible you plugged them into the wrong places (yes you can do that). Make sure you've "burped" the coolant system completely, as an air pocket WILL mess with the IAC. Once you've done that, pull #13 fuse out of the passenger side fuse box to clear the codes, and run it again, to see what codes come back.

 

[lothian]

...maybe unplug the ecu and plug it back in and that might clear the issue, but I haven't found where [the ECU is].

the ECU is in the center console, mounted above the "hump"; you typically access it from either the driver or passenger side kick panel. that said, you don't need to go near the ECU for any reason.

your buddy is wrong. cutting power to the ECU will clear the DTC codes, but it will not "clear the issue". that's not how things work.

you can clear data stored in the ECU volatile memory by disconnecting the positive battery lead, by pulling the ECU fuse, or connecting an ODB2 scan tool that has an "erase codes" feature. you clear the ECU as part of t'shooting DTC's, and/or to clear codes that the ECU will not clear by itself.

since pretty much all engine-work begins with disconnecting the battery, data stored in the ECU cleared when it's time to start the car. thus, the occurrence of the MIL at startup--or shortly thereafter--doesn't indicate that the ECU needs cleared again. it means the ECU is doing its job by processing data sent from the various sensors and reporting errata.

 

[lothian]

Try swapping the plugs from the MAP sensor and TPS sensor... it's possible [to plug] them into the wrong places (yes you can do that)

that's interesting. i had no idea that was possible.

 

[capsidx]

that's interesting. i had no idea that was possible.

It is possible but the TPS is blue and the MAP is grey so it would be obvious if they were mixed up if you took a picture for reference or have good memory.