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Discussion Starter #1
For the past 3 months or so I have had an intermittant bouncing idle that I have been unable to isolate a cause of. I am a trained Ford Technician but I don't deal with newer Honda's very often. The issue acts almost exactly like a faulty FITV (fast idle throttle valve) issue from older Honda's like my 98 Prelude. It wont throw a check engine light and I don't have access to a scan tool that will read parameters with a fast enough refresh rate to keep up with the bouncy idle.

The car: Stock 2006 Acura TSX 6spd manual with appx 118k miles.

What Happens: The car will drive normal above 1500 rpm and accel quite well without any hiccups, hesitation, or misfires but when it drops down to idle it will stay constant at 900 rpm inticated briefly then dips to 3-400 rpm then shoots up to as high as 2000 rpm. Not always consistant the highs and lows can be quite eratic and seem to have no pattern to inputs from the clutch, brake, ac, or electrical draw.

When it happens: More often in colder temperatures, but normally 3-4 times a day on my 30 mile round trip commute containing mostly city driving. Most often noticeable when the car is warm but not hot. Basically after there is enough heat to bring the needle about a 1/4 way up but before it kicks on the radiator fans at full operating temp. The symptoms are worse when the temprature is around 40* or colder, and by that I mean more frequent and more violent.

What I've done so far: I have smoke tested it a few times and have been unable to find any vacuum leaks, but the bouncy idle normally stops by time I can hook up the machine which may be skewing the results. I hooked up a vacuum guage and the pressure is high when the idle is dropping and is momentairly lower when the idle is raising but starts to go high again as the idle reaches its peak.

I have attempted to monitor the intake air temps, throttle position, and pressure pids via a scan tool but I can only get IAT to come up on my avialable scanners. The IAT reads consistant within +/- 3* of actual temperature and does not dip or change drastically or unexpectedly.

I also tried isolating vacuum lines to see if I could find an internal leak that would not show up with a smoke test and plugged the brake booster resulting in no change, and motor mounts which seemed to make the bounce less severe but didnt change the frequency of the issue.

The problem started about 4 months after I have done any work to the car and all maintence items have been serviced by me at 104k miles when I purchased the car. I have checked coolant level (recently flushed with new Honda type 2 coolant) and it is full and not leaking. Performed tune up with fuel service and new OEM NGK plugs, and changed the filters. Cleaned the throttle body and installed new throttle body gasket (OEM), checked the new gasket recently and it is not torn or folded. I have not done a valve lash adjustment yet but there is no noise comming from the engine to indicate a valve lash issue. Compression test was even across the board and the car baselined at 182hp/152tq which was higher than expected for the dyno being used by about 10hp.

Any Help is appreciated, I will attempt to load a video shortly.

Thanks, Nathan
 

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Discussion Starter #2
Here's the only video I have on my new phone, I will try to get another video whenever possible or figure out how to retrieve the others off my broken phone.

 

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Given what you have done already and nature of the issue I would assign less priority to potential vacuum leak. In general I find those pretty constant. Also watching your video, I can't get the engine sound, but that RPM movement feels un-natural, it is falling down like it is on fast forward, is engine actually in sync with that needle?
My gut feel points to electrical issue, most likely iffy connection, intermittent ground. These new cars in general control everything through ECU (completely). I am not sure, but I would guess that DBW circuit is responsible for idle duty and load compensation.
How is your battery? Alternator? Any corroded junction points? How is the negative terminal on the battery?

Good luck!

Nino
 

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Discussion Starter #4
I'm definitely looking towards an electrical or component concern. I stopped driving the car for a few weeks while I was enjoying the last of the good weather in my Prelude and with the change in temperature it has gone from annoying to concerning.The problem is my lack of reference materials. The battery tested good last month above 500 CCA and there was no noticeable A.C. voltage in the charging system. If I have time today I'll retest everything and recheck the throttle components.
 

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keep us updated, i have similar symptoms right now although i have a few ideas of what it might be from the list of checks stated above.
 

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Discussion Starter #6
And yes the engine is in sync with the needle. On the rev down the car feels like it's stalling and saves itself at the last moment.

I was thinking about what other work has been done to the car and I did take it in to the dealership for the power steering recall right before the temp dropped and the problem started. I am assuming that the computer adjusts idle with inputs from the power steering pressure sensor just like OBD 2a Honda's do. If that is the case then I'll check out the sensor to see if it was damaged during the recall. I bought it early February this year and it didn't have the issue then.
 

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Discussion Starter #7
As usual, it's allways better to **** it up yourself than have (or worse pay) someone else to **** it up for you. Checked out the charging system and everything was OK, so I went on to the line that was replaced for the power steering recall at the dealer and found the p/s pressure sensor to be partially plugged in. Was able to get the car to idle erratically on the lift and plugging in the sensor stabilized the idle at a normal level, and unplugging the sensor stabilized the idle low.

Afterwards I drove the car about 30 miles without issue and I'll probably put another 100 or so on it over the weekend. So I'll update in a couple of days.
 
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