Novak Conversions Jeep Wrangler TJ engine mounts

Engine misfire codes, high idle

TJuser

TJ Enthusiast
Original poster
Joined
Dec 14, 2023
Messages
165
Location
Ontario
Any help on this would be appreciated. 2003 tj sport, 4L.

I've got the following codes displaying
P0300 - multiple misfires
P0304 - cylinder 4 misfire
P0420 - catalyst system efficiency below threshold bank 1
P0155 - o2 sensor heater bank 2 sensor 1
P0161 - o2 sensor heater bank 2 sensor 2
P0138 - o2 sensor heater bank 1 sensor 2
P0306 - cylinder 6 misfire
P0432 - catalyst system efficiency below threshold bank 2


Now the 2 catalyst codes would be because I've ripped the cats out a while back, so I'm not too concerned about those. In addition to the heater and misfire codes though, the jeep will sometimes hold at 1500-2200 rpms after I let off the throttle and not sure if it's related, but the odometer will sometimes go dimmer or brighter.

I replaced the spark plugs about 20000 kms ago with the auto light iridium tipped plugs (or whatever ones were recommended on this forum, can't quite remember)

Is this a grounding issue or something else?
 
Addressing the engine speed hanging at 1500-2200 RPMs; that is probably a dirty IAC solenoid.
To fix that you can use a throttle body cleaner (Sea Foam or similar) and spray into the port (above throttle plate) for 5-10 seconds with the engine idling. Perform this procedure several times and then rev the engine and see if the RPMs responds properly.
Not fond of the Iridium spark plugs in the Jeep 4.0L; I prefer the NGK V Power spark plugs.
 
Is this the first time in a long time since you've read the codes? Might want to clear them out and see what returns.

-Mac

Crap, sorry I didn't get notifications on this, sorry.

I cleared out the codes when I first got the misfires, which they've returned. I think one of the o2 sensor wires is disconnected which is why it'd throw the heater issue too. I'll patch that up and see.

Addressing the engine speed hanging at 1500-2200 RPMs; that is probably a dirty IAC solenoid.
To fix that you can use a throttle body cleaner (Sea Foam or similar) and spray into the port (above throttle plate) for 5-10 seconds with the engine idling. Perform this procedure several times and then rev the engine and see if the RPMs responds properly.
Not fond of the Iridium spark plugs in the Jeep 4.0L; I prefer the NGK V Power spark plugs.

Ok I'll give that a shot. I did pull it and clean it with brake cleaner a bit back.


You can also see the fuel trim, not sure if that helps. This is at idle
20250103_141636.jpg
 
Novak Conversions Jeep Wrangler TJ engine mounts