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Discussion Starter · #1 ·
I went to the store to buy some throttle body cleaner then came back. No problem during that drive.
Came home, took the air box off and then the rubber boot that connects to the throttle body. Left the throttle body installed but depressed the gas pedal to open up the butterfly valve in order to spray and clean it. Hooked everything back up and now it won't start. Video linked below. What could be the issue? There was a mass air flow code and an intake air temperature code because the MAF sensor was disconnected while I cleaned the throttle body. I cleared those before trying to restart the car.

No start video
 

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Discussion Starter · #2 ·
well, should have looked this up before posting. It was probably the cleaner fluid that made it past the TB which flooded the engine. I re-tried the start with my foot fully on the gas pedal and it started up. Took it around the neighborhood for a test drive and unfortunately, cleaning the TB and replacing all vacuum lines still does not fix my intermittent RPM drop issue. Might have to take it in for a diagnostic. After getting back home I also saw that there is a pending P0300 code which wasn't there before. I'm also guessing this is due to the cleaner fluid burning off and will hopefully just resolve itself, since it wasn't enough to properly trip the CEL.
 

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I believe driving a bit more will return idle to normal as the computer relearns the new situation with the TB ( unlike my sons 2010 Civic which I had to reset the throttle position sensor with my diagnostic machine). Also it is not good practice to spray the cleaner into the TB as the fluid could migrate via the shaft into the electronics and cause issues. I believe there was a TSB for that . A better practice is to spray on a piece of rag and clean the areas as best as you can. I have not had any issue s-l-o-w-l-y rotating the butterfly manually ( ignition off) and wiping the inside of the TB . Regarding the intermittent RPM issue , have you tried fuel injector cleaners? Run a few bottles and see what happens. If the injectors are sticking open more than they should then your engine gets flooded causing a drop in rpms...just a thought.
 

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Discussion Starter · #4 · (Edited)
I haven't tried injector cleaners yet. My RPM drop is a really weird one, but I am able to consistently reproduce it. Driving around 35-40 mph, downhill or flat (not uphill), RPM at around 2000. When I release the gas pedal (but no brake), the RPM will drop as normal, but when it reaches around 1500 it will quickly dip to around 1000 then again quickly jump back up to 1500 and stay there. If I tap the gas pedal, it will briefly go up (as it should), drop again to 1500, then do that quick dip to 1000 and back again. I don't think the transmission is shifting here and I don't really feel any surge or jerk when this happens. I don't have this issue while at idle or at higher speeds. Your comment makes me think that there could be a good chance that the fuel injectors are staying open longer than they should, as it only happens when my foot comes off of the gas pedal.
 

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What year is your Sienna? How many miles?
 

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Discussion Starter · #7 ·
adding videos of the RPM drop

RPM drop video 1
- The sound is the beginning is me taking my foot off the gas pedal. You can see the RPM doing a dip down to around 1200 before bouncing back up to 1500. I am not pressing the brake or giving gas at this time.

RPM drop video 2
- I'm giving steady gas until 0:02, then releasing. RPM does a quick dip from 2500 to 1900, then does a slow drop to around 1500, then does another dip to 1200 before coming back to 1500. It remains steady until 0:11 when I give the gas pedal a tap. It jumps to 1900 then dips right back to 1500 when I release. Then it does the dip to 1200 again before going back up. On the final pedal surge at 0:17, RPM jumps to 1900 then back down to 1500 but does not do the dip as I think it's outside of the speed range where this triggers.
 

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Hey, 2009 LE with 133k here. I have noticed similar behavior in similar situations at similar speeds. I've noticed the transmission "hunt" just like in your videos. If I remember correctly, it is usually just after I take my foot off the gas. I've never thought much about it. I'll try to keep an eye on it and let you know if it shows the same "dip" that you're noticing. I wouldn't be too worried about it, though. I've chalked it up to the system trying to figure out whether it should assist in using engine braking on a downhill slope.
 

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Discussion Starter · #9 ·
yeah, it's making me wonder since it only happens right after I take my foot off the gas, and only when on a flat or downhill where the car doesn't just start slowing down immediately. otherwise idling is totally fine and no other RPM issues. I'm tempted to just use some fuel injector cleaner for good measure but let it be and just keep an eye on it for another fuel tank cycle.
 

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It may also be your fuel pump or a pressure regulator or a sensor which is causing the dip/surge. It does sound like a vacuum leak though, although I would expect that to behave similarly at other speeds/RPMs like coming to a stop on a cold/wet morning if it were. There's also a possibility that your transmission is sticking/slipping, so it wouldn't hurt to do a drain and fill if it's been at least 15k miles since the last one.
 

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Discussion Starter · #11 ·
I just replaced all the vacuum lines so sure hope it's not a continued vacuum leak issue... The curious thing is that this specific condition is the only time I can trigger the RPM dip/rebound. Idling and other driving conditions are fine. The trans fluid was drain/filled about 600 miles ago. I still have about half a tank left, so I'll wait a bit and give fuel injector cleaners a try.
 

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Discussion Starter · #12 ·
Had a shop check out that behavior. They hooked up a reader and monitored the engine module. Nothing obvious came up. RPM rebound does not correspond with changes in air flow rate or fuel rate. Then they looked at the transmission module, and the timing of the RPM drop as per the video exactly coincided with the transmission solenoid quickly turning on and off (or maybe it was off and on). They said it is normal transmission behavior.
 

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The issue started after you cleaned the throttle Body (TB). The rpm fluctuations are not normal. If you are in park with engine idling , what happens if you bring the rpms up to say 2-3k then back off the accelerator? Do the rpms drop then go back up rather than a smooth decrease to idle rpms?? In the past when I cleaned the TB on my 06 I never experienced what you are experiencing now and that is probably due to my regular maintenance, that the TB was never in a bad shape ( carbon build up) to see a noticeable change when cleaned However with my sons 2010 Civic it was the first time cleaning the TB (100k miles) which resulted in the similar issue you are having. My gut feeling is that the Throttle Position Sensor (TPS) needs a reset. The dealers wanted 100 bucks or so for a simple plug in ( diagnostic machine) couple inpus on the machine to reset the TPS. I opted to purchase a dedicated bidirectional diagnostic tool (Foxwell NT510 elite with Honda software) and used it to reset the TPS. It was easy enough to do , and the RPMs were back to normal. The computer is confused having gotten familiar with the "old normal" with carbon build up in your TB. Now it sees a new situation but still behaves with the old memory. Your transmission may be shifting normally as you said but I think its your TPS that need resetting. My 2c.
 

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Discussion Starter · #14 ·
You have the timeline a little mixed up. The RPM issue was there before. Changing out the vacuum lines and cleaning the TB were steps of trying to address it. Having a shop take a try was the last step. The only time this RPM thing happens is in the scenario I wrote above. Nothing happens at idle.
 

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Edit: I posted too soon. ^

...unfortunately, cleaning the TB and replacing all vacuum lines still does not fix my intermittent RPM drop issue.
 

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yeah, it's making me wonder since it only happens right after I take my foot off the gas, and only when on a flat or downhill where the car doesn't just start slowing down immediately. otherwise idling is totally fine and no other RPM issues. I'm tempted to just use some fuel injector cleaner for good measure but let it be and just keep an eye on it for another fuel tank cycle.
I tested my van yesterday. Same speeds (35-45mph), flat or downhill, low throttle, and I see exactly the same drop when I let off the throttle. From what I remember, one time it bounced 1600 to 1200 to 1600, and then another time it was 1500 to 900 to 1500. I'm still not concerned about it.
 
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