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Discussion Starter · #1 ·
Our 2006 Acura MDX with 129k has been giving us check engine lights stating a misfire in all cylinders routinely for months and we can’t figure it out. Any suggestions?

BACKGROUND:
The CEL & sometimes VTM-4 lights stared coming on soon after replacing the timing belt, water pump, spark plugs (Denso Platinum - OEM) and an engine mount. The codes say every cylinder is misfiring.

We replaced the coil packs with OEM ones from the dealer. Two weeks later, same code. The CEL was reset a couple of times by shops when they evacuated it, but every two weeks... it comes back on. After 3 or 4 tries with our Honda/Acura Indy shop, they suggested we go to the dealer.

After tons of research, everything we read on the forums determined that it needed a valve adjustment, which is the common fix for this issue, and is recommended by the owners manual at 105k. We took it to Honda and they suggested the same thing (without us feeding them the idea), and said the valves may need to be replaced if the light comes on again. We left satisfied and confident we finally fixed the problem, but the very next night... the light is on again.

I thought about an EGR replacement, and I could ask the dealer about the potential valve replacement they suggested, but I’m getting so worn down by this car that i suppose I’m losing hope.

Do you have any ideas?
 

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Hmmmm...to me it almost sounds like the timing belt was installed incorrectly... like it's one tooth off...I believe the symptoms are the same if the timing belt skips a tooth (misfiring on all cylinders). Hopefully I am wrong and it's something simpler :)
 

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A few ideas:

I would check/clean the throttle body. Check this forum and YouTube for how to. Don?t use carb cleaner, use throttle body or throttle plate cleaner, and don?t spray it in the throat. Wipe.

I had a misfire fire/stumbling problem and traced it to my fuel pump. There?s a post on this forum. My symptoms were whenever the car sat for more than 1 hr cold or hot engine, it would stumble and misfire at start up. Basically, the pump wasn?t holding fuel pressure so the injectors were not evenly pressurized and delivering fuel. A basic check would be when ever the car hasn?t been started for 1 hr plus, put the key to position ll for 2 secs, then repeat a couple more times. That will pressurize the fuel line. If the misfire goes away, it?s probably your pump.

Could be dirty or bad injector.

You?ll need to reset your CEL each time and see if it comes back on. This forum has the method.

Good luck!
 

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I'd add that swapping out the PCV valve might be a good idea (it's dirt cheap and dead easy).

I'm also betting that your timing belt is off a tooth somewhere, based on the fact that valve adjustment didn't help, and that it happened right after swapping the timing belt. It would be really easy to get one or both of the cam pulleys off a tooth. Won't be a lot of fun to fix, but at least it should be pretty easy to check (you can see the timing marks more or less through the little rubber plugs on the side of the heads on the passenger's side of the engine. Line 'em up and see if your crank pulley market is pointing toward TDC.

And FWIW, I will never suggest replacing all the coils - the chances of having six bad coils are about the same as being hit by lightning - theoretically possible, but it never happens. Once in a great while, a single coil will fail, but it's easy enough to troubleshoot by swapping it with a neighbor and checking to see if the problem stays on the same cylinder or follows the coil pack. Only then replace the one bad coil - new ones are actually more likely to fail than the old (tried and true) coils.
 

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Discussion Starter · #5 ·
All good suggestions...but hopefully I won’t have to try any of them right now.

We took the car back to the dealer this morning, and they said the valve adjustment wasn’t done on Friday, even though we approved the work and verified point blank that it was done prior to driving off. They are stating that they charged us for the diagnostic and a “software update”, and nothing else. You can imagine my initial reaction.

We are debating with them right now on how we are going to proceed, but will probably pull the car and go to another shop for the valve adjustment.

Here’s to hoping that the valve adjustment fixes the issue. If it doesn’t, I agree that the timing belt may need to be looked at again...because the first CEL happened a few days after the belt job, it’s affecting every cylinder, nobody can seem to diagnose it.

I’ll keep you all posted on what happens next.
 

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Should be easy for your shop to check the belt timing as habbyguy says to verify the timing isn?t off. And if it is off, own up to it and fix it.

I don?t know what a timing belt + valve adjustment cost at a dealer, $800-$1000 + $600-$800? More? Hopefully they didn?t charge you for both.
 

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Discussion Starter · #7 ·
The new dealer says the EGR valve needs to be replaced. Valves haven’t been adjusted. Quoting my spouse who spoke to them, they started from scratched and blocked the EGR valve off..and the misfires stopped, so that should fix it.

Prior to taking it to either dealer, I️ asked the original Honda/Acura Indy shop that did the timing belt change a few weeks ago if the timing may be a tooth off and they abruptly said “there’s no way (timing being off would cause my issue)” and that’s when they suggested I️ take it to the dealer. They have always been good about going above/beyond, correctly diagnosing issues, and meeting expectations, so it it kind of took me back that they were so flippant about it.

I️ was hoping the dealership would point to the timing belt so I️ could return to the Indy shop with a stronger finger to point, but if the EGR valve is truly the issue, I’ll go with it for now.
 

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Just to share my experience of misfiring and hope it can help you to address the issue.

Because of the clattering noise from the engine, which means valves are too loose, I had the valve clearance adjustment done, by a bad mechanic (which found out later). The bad guy didn't follow the correct procedure, and adjusted most of the valves too tight. Immediately after that, I got CEL on and misfiring code from ALL cylinders: P0300, P0301, P0302, P0303, P0304, P0305, and P0306. And the engine vibrated roughly at idle speed.

Then I found a good mechanic who re-did the valve clearance adjustment yesterday. I watched him setting all valves clearance to the specs. Now CEL is off, no misfire code after reset, and the engine runs smoothly.

So, valve clearance too tight does cause misfiring and CEL. However, for the timing for your CEL/misfiring, I doubt it's the tight valve caused the issue. It's suspicious to me that your shop sent you back to dealer for the valve clearance adjustment. Any qualified mechanic should be able to verify and/or adjust the valve clearance, way cheaper than the dealer.

At 129K, the X is due for valve adjustment if haven't been done. I got mine done at about $280 at YourMechanic.com but you have to watch them to avoid bad work.

Coils cost way too much at dealer ($80 each) comparing the same OE one at Rockauto (Denso $38 each). 2 of my coils were in very bad shape, even the "bad" mechanic told me no need to replace.

Although I really not sure if incorrect timing will cause misfire, but I buy that point. So, if you still trust your shop, ask them to verify/adjust valves, and go from there. Otherwise, got a 2nd opinion. My 2nd "good" mechanic has almost 40 years experience and really good review. I trust him immediately once I met with him and had some conversation.
 

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Discussion Starter · #9 ·
Happy Thanksgiving to everyone.

The dealer reported back. The EGR valve didn’t fix the issue, and neither did the valve adjustment. They can continue checking it out ($100 an hour to explore), or we can take it home.

It’s coming home with me. We are out of ideas for now. We bought it from my parents at a huge discount, so I️ might need to explore handing it off to someone else while I’ve still got equity.
 

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So have you verified the timing belt installation? See the link below:
https://repairpal.com/misfires-and-their-causes

Also the spark plugs. Did they use the right plugs? Did they set the gap right? It should came with right gap from factory by default, but who knows. The OE plug for 06 MDX should be Denso SKJ16DR-M11 Iridium Plug, and you said your shop used cheaper platinum one???

The engine on MDX should be very stable. Since you got ur X from your parents, you should know it has been well maintained. As a general troubleshooting procedure, at least in computer area, the first thing to check is what changed right before the issue. In your case, the timing belt/water pump/spark plugs service.

You may give YourMechanic.com a try, and I believe they charge $70 for misfire diagnose. However, you have to check the mechanic's profile and review.

So, with the issue you had, how does your MDX drive? Smooth? vibrate? MPG?

Hope you can get your X back to track soon.
 

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Discussion Starter · #11 ·
I️ will check out that link when I️ am back with the car and see what I️ can figure out myself.

I️ actually suggested to the dealer that they double check the spark plugs before we pick it up to make sure a second pair of eyes checked it out.

We did get it from my parents, but they had it about 2.5 years (second owners) until my father bought something lower miles to prepare for his retirement.

The independent shop that did the timing belt change, so far, is uninterested in checking again as they feel our issue isn’t related. They are closed for thanksgiving, so I️ will definitely be following up Monday to see what I️ can work out with them.

The MDX seems to drive okay. It’s not incredibly smooth, but it’s also not rough. What is tricky for me to tell is how it’s SUPPOSED to drive. The week I️ got it, I️ sent it to the shop for the timing belt and all the 100k maintenance, and that’s about the time when I️ started having issues. So I️ can’t compare a before/after very well. The MPG is definitely 15 City though, almost all the time. Highway brings it closer to 20mpg.
 

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Hors3y, if I'm reading your last post correctly, the valve adjustment was done at the dealer, correct? Did you tell them your suspicion about the timing belt alignment being off? I'm thinking that the mechanic would have checked that or if it wasn't mentioned, hopefully noticed that something was off since as the engine has to be rotated to each cylinder to adjust the valves.

Not sure if you had to pay for it but if the EGR was ruled out, that's good.

There's a number of other potential causes for misfire but depending on how mechanically inclined you are, you might check the following. If you don't have a lot of experience working on cars, #3 is probably the only one to try. There's a whole host of safety and method involved so don't take my post as a how-to. I listed a few but you might want to search for more YouTube videos.

The idea is to troubleshoot by doing one change at a time and see if the misfire is resolved. Each time you do the change, you reset the check engine light CEL (explained below).

1. Confirm good spark - spark plugs are in good condition and tightened correctly

First check the plugs in 1, 2, and 4 for correct tightness. If not tight, tighten and reset the CEL, check for misfire. Usually takes at least 3 starts or 3 short trips to trigger the CEL.

If they are tight, remove them the plugs from the misfiring cylinders and swap them with another cylinder. Reset the CEL and see if the misfire goes to another cylinder. To get to the plugs, you have to remove the coils by unplugging them and using a 5mm or 6mm Allen wrench (sorry can't remember exactly). You can inspect the coils visually for cracks and burning. They could contribute to the misfire but like habbyguy says, low chance this is the problem.

If the plug swap didn't do anything, do the same with the coils from 1, 2, and 4, swap them with another cylinder. Reset CEL, check for misfire.

If the misfire switches places, it could be those plugs or coils.

If the plugs were not changed at 105K miles, you might as well replace them all (or have them replaced) as that's the recommended service interval. Use OEM plugs - NGK or Denso. (I used NGK 3657 in my 06 X.) Rockauto.com is a good source. If you go with them, search for a 5% off coupon code.



2. Confirm throttle body is clean

I mentioned this earlier. There is a throttle body on the engine with a plate that pivots to provide air to the engine for the fuel mixture. That plate is slightly gaped with the throttle body. If dirt builds up and blocks the gap, the air/fuel mixture can be affected. It's a pretty simple check and clean. You have to disconnect the approx 4 in diameter tube from the air filter that leads to the throttle body on the engine. Buy throttle body or throttle plate cleaner (not carb cleaner) at your auto parts shop or dealer and dampen a rag to wipe down the throat where the throttle plate pivots. Don't spray the cleaner and keep it off the shaft of the pivoting plate as there is grease on the shaft.
Engine must be off. Be careful to not get your fingers caught or pinched.


Reset CEL and check for misfire.

3. That the fuel pump is operating correctly

I mentioned this earlier also. Reset the CEL. The simple check is to put the key in position II for 2 secs a few times (4-6 secs total) before starting the X. This allows the pump to prime the fuel line. Do this each time before starting the engine. Check for misfire. If that seems to resolve it, your mechanic can check the fuel pressure. It could be your pump and/or injector(s). In my case, it was the pump. There's a write-up on this forum - you can search for, rough idle/misfire.

CEL Reset:

Make sure you have your radio and navi codes because you will need to punch them back in. Turn off lights, ac, fans, and radio. Disconnect negative battery cable for about 30 secs. Reconnect the cable. Start the X and let it idle for 7-10 mins to reset the engine computer and idle system. Idle for 10-12 mins if the engine is cold. Input the codes into the navi and radio.

Good luck and Happy Thanksgiving!
 

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A few things to consider (an overview of misfire codes)

1. The computer does not directly detect actual misfires in most OBD2 designs. It simply monitors crankshaft speed fluctuations. When excessive fluctuation is observed, the computer reports a probable misfire and tries to interpret which cylinder(s) are creating it.

First 2 minutes of this professional training video explain it: https://youtu.be/4iYBzP3kUjk


External mechanical problems can cause the misfire codes to set even when there is no actual misfire. Examples are transmission defects, driveline defects, torque converter defects, loose or failing crankshaft speed sensor, etc. The important point here is that misfire codes can be false.

2. Improperly timed camshafts can result in actual misfires. As already posted, it is quite simple to confirm proper camshaft timing by looking at the alignment marks on the cams and front crankshaft pulley. At this point I would do that next.

3. Mild "misfires"* will set the CEL on after a period of time. Severe "misfires"* will cause the CEL to blink while driving. Has your CEL ever done this?

*as already stated "Misfire" is just a detected crankshaft speed fluctuation that exceeds the programmed limits.

4. Best way to clear codes and reset the CEL is with an OBD2 scanner, not a battery disconnect. Cheap scanners are available at auto parts stores, Amazon, etc. Always worth having.
 

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Had almost the same issue. Car would misfire when cold and reversing (flashing CEL) but drives fine when in motion and no flashing CEL when warmed up. Check your PCV valve.
I had cylinder 4 misfire and sometimes 1 and 2. PCV valve is in front of cylinder 4.
You can take it out and shake it. It should rattle consistently, if not, try cleaning with carb cleaner, reinstall, and clear CEL.
I replaced my PCV, it's cheap and takes 10 seconds to change. Problem gone.
 

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Interesting subject that seems come up a lot. The CEL with the VTM lights together with multiple misfires. I have dealt with this issue with my '04 MDX and hope my experiences can help. I concur with LeftOverParts post above. Very good advise. Originally, I was getting the CEL light for a vacuum leak in the throttle body/air intake. I checked all connections multiple times and found no leak. So I changed the MAF sensor and the Ambient Temp sensor in the air intake, before the throttle body. Then replaced the PCV out which was definately clogged. The CEL light would come and go, so I cleaned the throttle body. Be careful if you do, you will have to reset the 'drive by wire' throttle position.

I changed these sensors because I wanted to rule out various causes and they are easier and cheaper to do myself. Finally the CEL light went away.

However, once cold weather started I started getting the CEL and VTM-4 lights the first time when the temp got into the low 40's. The VTM-4 would go away within a few minutes. OBD2 showed multiple misfires. Had the code deleted and the weather warmed up and no more problems. The next time it got cold though, BAM, the codes were back. Problem was, the car drove ok and shifted ok with no notable misfires. I was thinking of the valves and throttle body control as issues. The MPG had dropped a little too which I attributed to the cold weather. In the end, I replaced the Throttle Temp Sensor (after the throttle plate) thinking the idle might be too low on cold mornings. It was a $35 sensor and real easy to replace. So far, the warning lights have not come back and the cold idle is up to 1100 rpms cold. The MPG and smooth acceleration have improved.

At the same time as doing the above, I did check and tighten all the spark plugs, just in case. If the warning lights come back, I plan to pull the throttle body and clean the throttle body control valve and maybe the EGR. At the last timing belt change, my shop told me the valves looked ok, so that will be the last thing, if necessary. Oh, my MDX just turned 290k miles and runs good.
 

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I own 02 MDX with over 200K miles. It started showing CEL & VTM light on this year summer. Codes showing were: all cylinder misfires(P0300, p0301, p0303, p0306 with P0172.) I kept driving until CEL started flashing. I talked to local dealership and they gave me quote of $450 for just diagnostics. I also talked couple of other mechanics here but NO TIME till next week blah, blah. I wanted my MDX fixed before winter because both MDX and Pilots (owned earlier) disengage AWD system if VTM light comes on. So driving without AWD in AK icy roads is scary! SO I decided to trouble shoot myself. I started from the cheapest & the easiest things: Checked spark plugs, wires, cleaned EGR vale & ports, Throttle body, air filter, cleared air passage, cleaned MAP sensor. Rest the codes and drove for few days. Same Codes came back. Checked vacuum leak and Idle air control valve ( I noticed the idle wasn't staying at 1 or below so I changed the idle air control valve with an after market (original costs $300) Code rest; drove for few days P0172 was gone but misfire codes reappeared.
I sacrificed my next weekend and spent 6 hours on my open air driveway in chilling NOV of AK (No garage) I adjusted the valves and cleaned fuel injectors. Rest the codes and no problem so far. Driving smooth & strong as usual in AK icy roads! I just spent $100 for Idle air control valve! Wish you good luck and God Bless! oh yes, My MDX gives me 19 miles on icy highway roads, it wasn't going more then 11 before!!
 

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The recurrent theme through MANY posts here is that people with well over 100,000 miles on their MDX since new or the last valve adjustment report diminished performance and misfire codes. It really isn't an optional service - these cars NEED valve adjustments every 100,000 miles or so. Prolonging the interval just costs money since your gas mileage will drop, and if you let it go too long it can actually start doing physical harm to your valves.

The good news is that it's not a terribly hard DIY thing - it's only intimidating since you have to pull quite a bit of stuff off the top of the motor. But the process itself isn't all that difficult, though it's not for the truly ham-handed wrench twister. ;-)
 
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