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Old 08-29-2010, 12:16 PM   #1 (permalink)
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MDX Diagnostic Help Needed

My 04 MDX with 103K miles through out a bunch of codes last night. All 6 cylinders misfired:P0301 - P0306. Also through code P0300, a general misfire code, and P2138, a Throttle Position Sensor error. Plugs have under 10K on them, and I pulled 4 and they looked almost new. The 4 coils I pulled looked OK too. I cleared the error codes, but still have a problem. Highway mileage was 21-22mpg yesterday for 5 hours (before error code). A few weeks ago I ran Seafoam engine cleaner through the fuel system.

Symptoms: Engine runs/accelerates strong until 4800 RPM at Wide Open Throttle, then "rhythmically hunts" up and down between 4800 and 5000 RPM. It can't seem to get above 4800 RPM.

Suggestion or ideas? I really want to avoid the dealer if I can, but I am not prepared to adjust valve clearances. And no, I have not yet changed the timing belt, and was planning to do it in next few months.

Thanks.
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Old 08-29-2010, 12:20 PM   #2 (permalink)
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I forgot to mention that the VTM-4 light and the VSA light also came on when the Check Engine light came on.
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Old 08-29-2010, 11:24 PM   #3 (permalink)
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I'd replace the sensor related to P2138. Its probably starting to fail and causing the weird rpms.
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Old 08-30-2010, 11:10 AM   #4 (permalink)
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I would pursue that first. Unfortunately on the '04, it's an electronic throttle. Don't think the individual sensor is serviceable. So the entire assembly will need replacement which is probably $500 I'd imagine. Awful expensive guess.

I'd clear the codes, and if the P2138 comes right back, then that would make it a bit safer to assume that the throttle body assembly will fix everything.
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Old 08-30-2010, 12:42 PM   #5 (permalink)
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Is the TPS on the MDX adjustable? On other vehicles I've worked on, the holes for the TPS were slotted to adjust it to factory specs. If this is the case, could the TPS have moved and be out of alignment?
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Old 08-30-2010, 01:03 PM   #6 (permalink)
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Quote:
Originally Posted by kgantzer View Post
Symptoms: Engine runs/accelerates strong until 4800 RPM at Wide Open Throttle, then "rhythmically hunts" up and down between 4800 and 5000 RPM. It can't seem to get above 4800 RPM.
Your “WOT” comment is interesting.

How does it behave when slowly revving the engine to 5 grand in PARK?

This stuff is so interactive, but if O.K., could rule out an ignition or rev limit problem?
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Old 08-30-2010, 07:44 PM   #7 (permalink)
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Your “WOT” comment is interesting.

How does it behave when slowly revving the engine to 5 grand in PARK?

This stuff is so interactive, but if O.K., could rule out an ignition or rev limit problem?
Same behavior. I learned to day that the MDX has a rev limiter when in park or neutral (i.e not under load), and that was causing the RPM issue, as designed. Still does not explain the ECL and codes. I did buy some ethanol/gas in Kentucky, so perhaps there was some "bad gas" in the system, but there was no ECL until I used 1/2 of the full tank.

I'm gonna let it run and see if the problem comes back.
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Old 10-08-2011, 11:54 AM   #8 (permalink)
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A year later and the problem is back - P2138 code

Got all the lights again - still intermittent but becoming more frequent. I cleaned out the APP Sensor connector, just to be sure, then just ordered a new APP sensor from G1Parts.com for about $90 (w/ free shipping). Part number is 3791-RDJ-A01. Many Honda cars use this part, not just MDXs. So you can order it from Honda or Acura dealers, too.

Local dealers wants about $140 for the part, and another $150 for labor - total quaote of $290. Looks to be a simple DIY - maybe 30 minutes.
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Old 10-15-2011, 09:15 PM   #9 (permalink)
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APP Sensor Replaced

I installed the new APP sensor - only took 30 minutes. Very simple - just 8 different bolts to remove.

I followed the instructions found here: http://tl.acurazine.com/forums/showt...php?p=11244755

Now we'll see if my wife complains of another failure.
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Old 11-08-2012, 01:50 PM   #10 (permalink)
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Hi kgantzer - another year later now. I'm wondering if you still have had or experienced any more APP sensor issues since you replaced it a year ago? I am experiencing similar issues and mechanic said code is P2138. Think I will replace APP sensor myself today.
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Old 11-09-2012, 05:18 PM   #11 (permalink)
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Hi kgantzer - another year later now. I'm wondering if you still have had or experienced any more APP sensor issues since you replaced it a year ago? I am experiencing similar issues and mechanic said code is P2138. Think I will replace APP sensor myself today.
The problem is 100% gone.
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Old 11-12-2012, 11:19 AM   #12 (permalink)
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kgantzer - thanks for the info. i replaced my app sensor the day i posted my question to you and yes, experiencing major difference in acceleration operation. i did also noticed that the cable had a lot of slack on the old one. i almost wonder had i just tightened the old cable that the problem would have been solved. but since i had already purchased the part i went ahead and replaced the app and tightened the cable and now it is much smoother.

recommend any one else experiencing this problem to first go ahead and tighten the cable if it is slack. (that just involves removing plastic cover to get to the cable) that may be the culprit. then if that doesn't work replace the app sensor.

very easy diy job.
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Old 02-23-2013, 10:52 AM   #13 (permalink)
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We have a 2005 MDX Touring about 97K+ miles and now P2138 code, VTM4 and VSA indicators all light up.

Is there a specific part name for the app sensor?
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