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Discussion Starter · #1 ·
Howdy MDXer's! Been lurking for a bit and gleened a lot of info however I'm stumped. I'm hoping someone chime in w/ some ideas.

At idle the the rpms fluctuate up/down, with the RPMS ranging between about 750-900. There is a constant 150-200 rpm bounce. The vehicle starts w/o issue but in gear or park it has the rough idle. When in gear, accelerating smoothly it does so evenly but it feels under powered. At 60 mph it needs to down shift to go over even small over passes.

When traveling at low speeds, 40mph and/or if the RPMs are below 1800, the RPM gauge jumps and I can feel the surging. At 30mph the vehicle does Not buck but the rpm gauge moves like a metronome.

-2002 MDX w/ 182k. The trans TSB was done immediately after the TSB was issued. The vehicle was acquired for next to nothing as it was very dirty and had damaged suspension parts. A weekend in the garage corrected the broken arms but the idle problem is a puzzler.

The following has been done for maintenance and in a hunt to solve this issue.
-Oil/filter replaced
-air filter replaced
-coolant flushed
-spark plugs changed (idle improved significantly, was really bad initially, all plugs were in bad shape)
-EGR system cleaned
-Throttle body has been cleaned as well.
-2 tanks of fuel w/ 104+ octane added as well as cans of Seafoam each time.

There are NO codes. I can pull the MAP connector and it dies and I get a code. The TPS can get disconnected, it idles widely and throws a code. I clear the codes reinstall the plugs and its back to "normal" rough idle.

I do a live scan and the O2 sensor for B1S1 has voltage all over the place so i'm thinking O2 BUT the PCM does not have an O2 sensor DTC. I can see the fluctuation during the live scan BUT I don't know if the rpm surge is causing the O2 to read the surge or the O2 is going out and it's causing the surge. I'm great w/ diesels but this is causing me to ponder.

I do recall when doing plugs they looked fouled so I'm wondering if the O2 is out/going out thus causing the surge and contributed to some fouled up looking plugs.

I'm open to ideas
 

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This is way above my pay grade, but a few random thoughts:

Have you cleaned or replaced the PCV valve?

I would be pricing out a torque converter repair. But that's gonna hurt. Does the trans shift OK? No evidence of cross-contamination of ATF and engine coolant? The ATF cooler in the radiator is a known failure point ( actually it's connections that fail, but the effect is mixed fluids... so-called "strawberry milkshake of death" ). Before anything else, I would do a "3x3" ATF change ( 3 changes of about 3 quarts each time, with a short drive in between changes ). Acura doesn't recommend power flushing.

O2 sensor wouldn't be a surprise, but dunno why it isn't throwing codes. Much cheaper than the torque converter as a next step, but might be unnecessary.

Have you checked compression, and checked for exhaust leaks?
 

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Howdy MDXer's! Been lurking for a bit and gleened a lot of info however I'm stumped. I'm hoping someone chime in w/ some ideas.



At idle the the rpms fluctuate up/down, with the RPMS ranging between about 750-900. There is a constant 150-200 rpm bounce. The vehicle starts w/o issue but in gear or park it has the rough idle. When in gear, accelerating smoothly it does so evenly but it feels under powered. At 60 mph it needs to down shift to go over even small over passes.



When traveling at low speeds, 40mph and/or if the RPMs are below 1800, the RPM gauge jumps and I can feel the surging. At 30mph the vehicle does Not buck but the rpm gauge moves like a metronome.



-2002 MDX w/ 182k. The trans TSB was done immediately after the TSB was issued. The vehicle was acquired for next to nothing as it was very dirty and had damaged suspension parts. A weekend in the garage corrected the broken arms but the idle problem is a puzzler.



The following has been done for maintenance and in a hunt to solve this issue.

-Oil/filter replaced

-air filter replaced

-coolant flushed

-spark plugs changed (idle improved significantly, was really bad initially, all plugs were in bad shape)

-EGR system cleaned

-Throttle body has been cleaned as well.

-2 tanks of fuel w/ 104+ octane added as well as cans of Seafoam each time.



There are NO codes. I can pull the MAP connector and it dies and I get a code. The TPS can get disconnected, it idles widely and throws a code. I clear the codes reinstall the plugs and its back to "normal" rough idle.



I do a live scan and the O2 sensor for B1S1 has voltage all over the place so i'm thinking O2 BUT the PCM does not have an O2 sensor DTC. I can see the fluctuation during the live scan BUT I don't know if the rpm surge is causing the O2 to read the surge or the O2 is going out and it's causing the surge. I'm great w/ diesels but this is causing me to ponder.



I do recall when doing plugs they looked fouled so I'm wondering if the O2 is out/going out thus causing the surge and contributed to some fouled up looking plugs.



I'm open to ideas


Just a thought. So this is something to check only. I am not saying this is the problem. Everything you describe in detail (and I read it through three times) is identical to the symptoms I got on a previous car (different make): the rough idle, the bucking when accelerating, the fluctuating RPMs, the underpower when accelerating, etc. i am not technical so won't provide all the diagnostic details and this happened almost 10 years ago so my memory is foggy but ultimately I believe what the mechanic did is do a coolant pressure test after removing each sparkplug one at a time. They found coolant was leaking into one of the cylinders (something like that). Bottom line - the head gasket had to be replaced. It was very pricy and I had to leave the car in the shop for multiple days but after that no problems since.


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Discussion Starter · #4 ·
WL:
For the price ill do the pcv. I found a troubleshooting vid on the EGR so ill chk that out this week.

The transmission shifts fine, no slip or shudder. The I actually tracked down rhe original dealership and they preformed the factory tsb. Vehicle has had no other work done. The transmission fluid was full the day i got it and in past experience it won't contribute to the idle problem in park.

Thanks for the heads up on the milkshake and i have no desire to pull a fwd motor trans.

The exhaust seems fine, I did have to weld the cat heatshield back on and weld on a new muffler.

I haven't chked compression as there is no smoke at start, no smoke at idle and no smoke under load BUT its easy to do and its good to have #s.

I did have a work truck that had similar symptoms no dtc and it was the O2, thus my guess couple with the live data reading.

TG:
I wouldn't have thought HG but when i do compression # Ill chk it.

Since pcv and O2 are expendable ill do the O2 as it is out of spec and ill follow up with the other tests.

Thx for the ideas
 

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I think the PCV valve is a good call - doesn't cost enough in $ or time NOT to do it. Same with cleaning the EGR valve.

I wonder if the car has had the valves adjusted. If it's over 100k without having it done, it's overdue. That can certainly cause poor idle, though I can't say it would cause the "metronome effect". Still, a really good idea.

I wonder if you've had a chance to monitor the vacuum while it's idling.

Carefully reading the pre-cat O2 readings might tell you whether the oscillations precede the change in idle or are a result.

Otherwise, if it was my car, I'd use my Torque app (works with an Android phone or device) and monitor everything I could, like fuel pressure or vacuum or O2 charting, etc. The next step (one I'd recommend if you're planning on keeping the car for a while) would be to get your hands on a HDS (Honda Diagnostic System) clone, and really dig into the systems. It's invaluable for diagnosing a lot of difficult problems, especially transmission issues (and we all need all the help we can get with those!!!). ;-)
 

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Discussion Starter · #6 ·
EGR ports, intake manifold and throttle body all cleaned.

There is an egr test I found and ill chk that tonight. I'll post the tech vid when I'm done.

The O2 is precat. Unless there's one im missing there is only a pre and post cat O2. That voltage is all over the place 06-.800. It will not hold stable.

At the moment post cat O2 sensor holds stable voltage.

Parts, pictures and live data only show two sensors but I could be missing something.

I haven't done a specific test for vacuum leaks however when I have removed a few hoses when running &it's obvious they're disconnected.
I will have to dig through the forms to see if there's a specific series of test just to cover a potential vacuum leak. I have seen it contribute to poor idle mileage and power on a dodge 5.8 360 so looking for potential vacuum leak makes sense.

I haven't adjusted the valves so I may have to tackle that next weekend.

The MDX had worn and damaged rear suspension parts so we got it knowing that would be a super easy fix. We've been pleasantly surprised at the amenities and how simple and easy the drivetrain was to work on. Plugs were done in under 30 minutes without any cuts, bruiseing or broken parts. It is easily one of the easiest cars I've ever worked on aside from what I think is an emissions related issue.

We'd like to get it running well then flip to get a newer one with less miles. Its a great bang for the buck vehicle; Honda parts are inexpensive, awd, leather, heated seats, steering wheel controls room for us and the dogs. I've already started looking for another :)
 

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It's normal for the pre-cat O2 sensor to bounce around - it's constantly adjusting to try to keep the fuel/air mixture around the magic 14.7 number. The quickest test you can do (assuming you have a monitor of some sort, which is why I recommend the Torque app so highly) is to compare the two pre-cat O2 sensor outputs with each other. Chances are overwhelming that you won't have the same problem on both (if there IS a problem there, that is), so you'll see a difference in the two systems.
 

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Discussion Starter · #8 ·
Been working late and its been raining like mad so i haven't had a chance to do any work.

When i last read the O2 data, the pre was all over the place. The post was .600-.800. Frim what i could find the pre # were out of spec. 14 bucks off fleabay, so we will see. Mileage wise the egr and O2 are probably shot.

Ill update my results.
 

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FWIW, the post-cat O2 sensors don't have much of anything to do with how the car runs, but just report whether or not the cats are doing their job (or not). Of course, a really bad all-over-the-place reading COULD be a sign of a clogged cat, but that usually shows up more at speed than at idle. The pre-cat O2 sensors are quite a bit more expensive - I did replace mine just as a prophylactic measure, since they were coming on 200,000 miles, and sensors are a lot cheaper than extra gas (didn't really make a difference at the time, but I know I won't have to worry about 'em for a loooooong time). If you're getting pre-cat O2 sensors for $14, it's a SMOKIN' deal (make really, really sure you're getting what you think you are - I've seen a lot of confusion on Ebay listings before).
 
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