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Discussion Starter #1
Hey everyone,

I just bought an 02 MDX, and I am experiencing an issue after driving for +-25 mins and slowing down or stopping. The vehicle is great when I first start driving, no issues. After about 25 mins and slowing down/stopping it is like the vehicle goes into limp mode. I accelerate, and the vehicle just won't go over 30mph. The revs don't budge. This happens for about 5 mins, and then it tends to start running okay again. It does not give me any codes. The cel doesn't illuminate.

The only issues I can visibly identify are;
  • VTM-4 light is illuminated
  • The speedometer doesn't work
  • The odometer doesn't work
  • The cruise control doesn't work.
The ride is smooth, the engine is quiet and when I am not having the issue described, the throttle is very responsive.

Please help!
 

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Looks like the common element is the PCM. That said, I hate just swapping out components without more troubleshooting to verify the problem. I'd suggest at least unplugging, cleaning and re-inserting the plug... with an intermittent problem like this, it's quite possible the problem is just a flaky connection. It won't be an easy one to troubleshoot in your driveway (unless the tach totally quits - can't tell from your description).
 

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Discussion Starter #3
I am sorry if I made it sound like the tach was going out, what I meant is that the revs don't spike, it's not like it dropped out of gear. It just won't go iver 2000rpm no matter how hard I push the accelerator.
 

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Does the engine make a deep, low grunt when you step on the accelerator and have no go? That's what a bad catalytic converter can do. How many miles?
 

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Discussion Starter #5
I haven't noticed one, but I will listen more carefully next time. It has about 93k miles on it. It feels like it's getting starved of fuel maybe... I don't know. It's confusing. I will get my husband to check the cats. Wouldn't they set a code though?
May be worth mentioning this car stood for 3 years, then got used for 3 months before we bought it.
 

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While rare, I've had a couple cars not throw a code with a bad cat. At 93k, doubtful it's the cats.
Habby did mention the PCM. On my old '04, the speedometer stopped working and the PCM was the culprit. Lotta stuff goes on in that little steel box.
After rereading your symptoms, it does sound electrical. Was the MDX sitting in a mice-type area for three years?
 

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Discussion Starter #7
Not sure where it was sitting. I am thinking electrical too. It seems to be inconsistent though. Some days I make it to work without the issue, some days I don't get 3/4 of the way before it starts. It seems to be happening less as the temperature drops... Wondering if it is heat related.
 

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Discussion Starter #8
So it finally set one code and has 2 pending. Set code is P0171, pending are P0170 and P1399. Any advice what could be causing this? Where to even start looking? I have read EGR valve, fuel pressure and vacuum leak... Any idea where to start?
 

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It's really hard to say - the rich condition can be caused by a lot of things, including those you mention (as well as a bad O2 sensor). I did a quick lookup and couldn't find P0170 or 1399 in the factory service manual (might just be a glitch because of the remote login I'm using right now).
 

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Discussion Starter #10
It's really hard to say - the rich condition can be caused by a lot of things, including those you mention (as well as a bad O2 sensor). I did a quick lookup and couldn't find P0170 or 1399 in the factory service manual (might just be a glitch because of the remote login I'm using right now).
0171 is lean.
0170 is fuel trim malfunction (bank 1)
1399 is random misfire (probably cause by lean conditions)

So I am thinking vacuum leak? Or blockage somewhere. But don't even know where to start finding the actual problem. My husband can do the work, but has only ever worked on Ford truck engines and tractor. He says the small engine scares him😂😂😂
 

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Vacuum leak would be a good guess. Sometimes you can find the leak by spraying some starting fluid on some of the likely locations - if there is a significant leak, it'll suck in enough starting fluid to cause a blip in the idle speed. Or he could hook up a full-featured OBD reader and monitor the vacuum (or hook up a stand-alone gauge - even Fords and tractors use those). ;-) I don't recall the specifics, but IIRC my MDX would idle around 20 inches of vacuum. Sorry, but I'm just not able to get to my "good data" from here...
 

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Discussion Starter #12
I had a thought... With the car standing for so long, is it possible that there is gunk in the fuel tank that blocks the screen after a period of driving? The guy we bought it from said he drained it and refilled it, but said and did can be 2 very different things in the world of private sellers. My husband doesn't want to lower the tank unless it is a possibility.
 

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Discussion Starter #13
Vacuum leak would be a good guess. Sometimes you can find the leak by spraying some starting fluid on some of the likely locations - if there is a significant leak, it'll suck in enough starting fluid to cause a blip in the idle speed. Or he could hook up a full-featured OBD reader and monitor the vacuum (or hook up a stand-alone gauge - even Fords and tractors use those). ;-) I don't recall the specifics, but IIRC my MDX would idle around 20 inches of vacuum. Sorry, but I'm just not able to get to my "good data" from here...
I need to get a fuel pressure gauge this weekend. Still difficult to diagnose when it only happens after driving for a while. Now that I am used to it, I can manage it by lifting my foot off the throttle and slowly depressing until the dying starts, and then easing up slightly. This doesn't help when you have to get through an intersection quickly... Lol
 

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Yeah, I could buy into a clogged fuel strainer / filter. If that's the problem, you can usually test it by trying to drive full throttle for a bit - if there's any restriction, it should pretty clearly starve the engine and cause it to run really rough under full throttle conditions. And my lawyer says to tell you to do this test on a racetrack only, a mile or longer. ;-)

If the car was setting for a long time, a new fuel filter would be prduent.
 

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Discussion Starter #15
Yeah, I could buy into a clogged fuel strainer / filter. If that's the problem, you can usually test it by trying to drive full throttle for a bit - if there's any restriction, it should pretty clearly starve the engine and cause it to run really rough under full throttle conditions. And my lawyer says to tell you to do this test on a racetrack only, a mile or longer. ;-)

If the car was setting for a long time, a new fuel filter would be prduent.
And I think we have a winner.... When I push the throttle to the ground the car just dies down like it is starving for fuel and starts throwing misfire codes on multiple cylinders. When I nurse it, there are no misfires, just lean condition. So I have ordered a new pump and that includes the filter from what I can see. We will drain and clean the fuel tank this weekend and replace the pump. Hopefully that makes a huge difference. Anything else I should check while we have the tank lowered?
 

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I realize you want to drain the tank to clean it but it’s a lot of work. There’s a hatch for the fuel pump under the middle row seat, drivers side. The carpet above the hatch will be pre-cut about 90%.

You can get loaner tools at Autozone or Oreillys to take the pump nut off.

I have a post on here when I replaced the fuel pump on our 06. The filter looked pretty clogged (and getting misfires.)

I was going to add make sure you relieve the fuel pressure and clean/lube the oil rings on the fuel line connections but sounds like you work on cars and would do that.

Good luck!
 

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Discussion Starter #17
So last night driving home my car suddenly was running rough and throwing about 8 different codes. Then the transmission started acting crazy. I barely made it home. My husband took the car apart and we found out that there is a coolant leak behind my dash, leaking straight onto the wires for the ECM. With it being winter and the heater being used a lot, I think this is our problem.
 

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I'm glad your hubby is a "real car guy" because the prospect of fixing a heater core isn't for the automotive lightweights! I agree that's probably causing your issues, and with any luck just cleaning and drying out the ECM will have "that part" of the fix done.
 

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Discussion Starter #19
So we did a temporary bypass on the heater coil, plugged everything back up and she runs beautifully. To get us through till we have time to pull the dash out. Crossing fingers, hope we are good.
 
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