Solved P0300 misfire only at idle.

[302nitrous]

so my 99 sport has a p0300 code

Random multicyl misfire.

The odd thing is, it only does it at idle. Has all the power throughout the rpm band, no hesitation under throttle or skip.

Just at idle

New plugs.
New wires
Cleaned MAF
Checked for vac leaks, non
Long term and short term fuel trim is right where it should be

Suggestions?

It’s a 302

 

[fastpakr]

Egr getting activated at idle?

 

[BrooklynBay]

Did you check the gap of the plugs before they were installed? Which brand did you buy for the plugs & cables?

 

[302nitrous]

Did you check the gap of the plugs before they were installed? Which brand did you buy for the plugs & cables?

Autolite 764, gapped at .030. Wires are the generic part store wires. Duralast

 

[302nitrous]

Egr getting activated at idle?

I tested the egr about 2 months ago when I had a egr code for insufficient flow. Ended up being the DPFE sensor. I took the vacuum fitting off the egr and it is getting vacume. Might go check and see if the valve is still good.

 

[fastpakr]

Is that .030 gap correct? I don't know the number off the top of my head, but that sounds narrow.

Edit - a quick search shows .054-.057. Might be worth checking.

 

[302nitrous]

Update: took the explorer to work last night to see if I could get another code. Used my tuner to monitorthe long term Fuel trim and short term fuel trim. The ltft is at +10-14% on each bank and the stft is at a steady -1 each bank

 

[BrooklynBay]

Gap the plugs to the proper specification.

 

[302nitrous]

Is that .030 gap correct? I don't know the number off the top of my head, but that sounds narrow.

It is a little narrow but I run them at a small gap due to the nitrous. So today I decided what the hell, gapped them at .040 and cleaned the grounds on the coil pack. Tested egr and it’s good. Started it up and it was realllly misfiring. Turns out the pigtail for the coil backed out a little, just enough to make it skip but not throw a code. put some electricle connection grease on the pigtail and pushed it all the way in. Cranked right over and idles nice and smooth now. Thanks for the input guys


Edit - a quick search shows .054-.057. Might be worth checking.

Gap the plugs to the proper specification.

 

[fastpakr]

Glad you got it sorted. I'd actually missed that this was a 5.0 swap and thought you were working with a V6. Figured the user name was about a different vehicle.

 

[BrooklynBay]

Thanks for the update. The title was updated, and the thread is now marked as solved.

 

[302nitrous]

Thanks for the update. The title was updated, and the thread is now marked as solved.

The plug gap was not the issue. I have sense gapped them back down to .030 for tuning with no issue

 

[BrooklynBay]

So what was the issue if it's not the spark gap?

 

[fastpakr]

It is a little narrow but I run them at a small gap due to the nitrous. So today I decided what the hell, gapped them at .040 and cleaned the grounds on the coil pack. Tested egr and it’s good. Started it up and it was realllly misfiring. Turns out the pigtail for the coil backed out a little, just enough to make it skip but not throw a code. put some electricle connection grease on the pigtail and pushed it all the way in. Cranked right over and idles nice and smooth now. Thanks for the input guys

His response earlier got buried in a quote of something I'd said.