[Kscott]

New plugs
Adjusted valves
All coils fire (and swapped around)
All injectors click
Cleaned injectors
Checked and cleaned egr
Cleaned map
All this brought the mdx from wouldn't idle to idle with a slight miss
#1 #2 and #4 have shown misfire code throughout

 

[LeftOverParts]

Couple suggestions, do them individually and check for misfire after.

Clean the throttle body - the throat and the edges of the plate that leave a small gap when there are closed. Don’t spray the cleaner, esp on the pivot shaft. Spray a rag and wipe.

Check for vacuum leaks. The front motor mount runs on vacuum and the mount can leak when old. You can try pinching the hose that runs from the front of the engine to between the radiator hoses to see if any roughness settles out. If not, check other hoses for cracks/leaks.

Btw, does it start right up or hard to start? Asking bc the fuel pump could be going bad. A little tricky but you can search how to test the pressure or look up the factory manual in this site.

Good luck!

 

[endrettohio]

I have 2003. I also am having misfire on 5/6 cylinders.
I did:
adjusted the valves
new spark plugs
new manifold gasket
sparkplug seals
cleaned the egr valve
cleaned MAP
It idles without stall ...dips a little but holds steady more than not....now when cold. I have a "Flutter" when in 5th when RPM's are under 2500 between 60-70 MPH It goes away if I shift into 4.
I don't always start up until the second try. Left Over Parts suggested fuel pump...? May have that to check that out. I was also thinking that I need a new Timing belt. I'm preparing myself for that DIY.

 

[Kscott]

Everything cleaned. No vacuum hookup on motor mount. Vacuum 12-13 but can't find any leaks. Starts right up but struggles to maintain idle when warm.

 

[notmycar]

would an overdue timing belt be a part of the problem?

 

[LeftOverParts]

OP kscott: It’s strange you have no vacuum line to the front motor mount. I checked rockauto and the mount showed a vacuum connection for 2002. By front, I mean behind the radiator, down low, middle of the MDX right/left. Yours’ might route differently but on a 2006, there should be a tube going from the engine and then a hose from the front of the engine crossing the gap between the eng and rad - then either a tube or hose going down between the rad fans to the mount. If it’s a tube between the fans, there should be a short hose connecting to the mount. Maybe yours routes differently and you’ll need to get under the engine and look for the mount and hose.

If it starts right up and doesn’t hesitate when accelerating (like onto a freeway) your fuel pump might be / probably is fine.

The valve adjustment can be tricky and if not done right, could result in misfire. If you had a competent shop do it or you’re confident it was done right, then probably not the cause.

There is a fuel pump relay and a separate ignition relay. Not sure if those could be intermittent or going bad. There’re fairly inexpensive on rockauto, expensive in brick auto parts stores.

If the TB ever broke, you could have bent valves. If ever overheated, a leaking head gasket. I suppose if the belt were really old, the timing could be off or varying. Keep in mind, it’s 105K miles or 7 yrs for changing. You definitely don’t want it to break.

Good luck!