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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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