*SOLVED* Misfires after new spark plugs and cleaning MAF

Joined
Sep 1, 2021
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34
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Whitefish, MT
1998 LX470, 265k miles. New to me, so I've been baselining even though it runs and drives great. Not much service done by the prior owner other than oil changes afaik.

Last night I decided to clean the MAF sensor and change the spark plugs. One mishap during the plug change - accidentally set my ratchet across the battery terminals for a fraction of a second. Negative battery cable was disconnected at the time so likely no issues from that.

Finished the job and fired it up greeted with an instant misfire code on cylinder 4 and shaking. Took everything apart and put it back together. My wire on coil for cylinder 4 wasn't pushed on all the way. Great! That must be it. Fired it up and felt some shaking, multiple misfire codes pending status (P300, P303, P306). Went to bed for the night.

This morning - clear codes, fire it up again and testdrive. MIL light blinking and misfiring still. This time codes P300, P303, P304, and P306. Take it back home and tear it apart again. P306 seemed to be coming on first and most often, so I swapped the coil on it with Cylinder 2. This time got codes P300, P303, P305, and P306.

Take it apart again. Inspect plugs and coils. All 8 are Toyota/Denso but two different part numbers - one P/N seems to have superseded another based on some looking at online parts stores. One coil was missing the rubber grommet. Also noticed spark plugs were Denso but not the OEM part number. Gap spec was 1.0 mm vs. 1.1 mm.

Took a trip to the parts store for OEM plugs and also picked up a NAPA brand coil so I could borrow its rubber grommet. Got a feeler gauge and checked all the gaps. All good to go. Went home and tore it apart again and put the new plugs in along with the coil grommet. Checked MAF resistance - slightly low for the 68F spec in the FSM but interpolated and it was in range for the 80F temperature in the airbox.

Put it all back together and fired it up. Still shaking. Misfire code P306 pending after a few minutes. Cleared it and went driving. During the drive I get P0300, P0303, and P0306. I've visually checked all hoses and wires.

Looking for help, have searched the forums and read through lots of ideas and tried a lot of things. Where to from here? Could one bad coil be causing codes on multiple cylinders? Is it possible I have multiple bad coils that weren't there before the plug change? Did I screw up the MAF sensor cleaning it with CRC? Is it possible I crossthreaded a plug or one is not sealing and is causing misfire codes on multiple cylinders? Did I fry something else with my ratchet on the battery trick? Should I throw the NAPA plug in cylinder 6 and see what happens?
 

JunkCrzr89

Competent Ignoramoose
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Jul 21, 2019
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Could one bad coil be causing codes on multiple cylinders? Is it possible I have multiple bad coils that weren't there before the plug change? Did I screw up the MAF sensor cleaning it with CRC? Is it possible I crossthreaded a plug or one is not sealing and is causing misfire codes on multiple cylinders? Did I fry something else with my ratchet on the battery trick? Should I throw the NAPA plug in cylinder 6 and see what happens?
In order: Yes, yes, maybe, possible but unlikely, maybe, yes.
 
Joined
Sep 11, 2017
Messages
356
Location
Bozeman, MT
I haven't had this problem on my rig. But if I did, I'd probably replace all the coils with new, and a set of new plug wires.
 
Joined
Sep 23, 2013
Messages
278
Location
Baton Rouge, LA
I had to chase something like this too for a while. Replaced all plugs, triple checked the gaps (make sure you don't drop any in the hole or the gap you just checked will close up, ask me how I know. Use the right socket with the rubber retainer and be gentle), replaced all coils. Purred like kitten. About a year later, started getting a weird code, very little threads here about it, turned out to be a bad MAF sensor, put new one in back to running like new.
 
Joined
Oct 21, 2020
Messages
63
Location
MS
I know you said you checked the rubber grommet but make sure you check the rubber boots on the tips of the coils. I was chasing a misfire on mine and it turned out to be a torn boot on the end of the coil. Sometimes the coils on the rear have to go in at an angle and this can tear the rubber boot because at this point they're not very flexible. This can cause the coil to arc inside the spark plug tube. Fortunately you can purchase a new boot kit and you don't have to replace the entire coil. The boot kit is bel 702521. You can get them at autozone for about $7.
 
Joined
Jun 14, 2021
Messages
125
Location
Phoenix, Arizona
I would try unplugging the MAF sensor altogether to test if it runs better like that. Obviously, that's going to throw its own codes, but you may see an instant improvement in the idle by just doing that.

If the boots look good all around and you're getting the codes for those particular cylinders, I would swap a couple of the coils around to see if the problem shifts to new cylinders.
 
Joined
Sep 1, 2021
Messages
34
Location
Whitefish, MT
5913ACDC-0A4D-4169-9B89-73A4C959BDF9.jpeg
I plugged in tech stream to get misfire counts. Confirmed suspicions that most of the issue was cylinder 6. Other cylinders only showed up randomly after driving and putting engine under load. Decided to swap out the coil with the Napa coil. While I was in there, noticed the connector to the injector was unplugged. :doh:. The little plastic tab on the injector for the connector to hook to is snapped off. Pressed it on nice and tight but that’ll be the first place I look if I have future cylinder 6 issues. The connector I’m referencing is in the pic. This is cylinder 8 but I was too lazy to take it apart for a hundredth time to get #6.

No more misfires felt or counted in techstream. Purrs like like the ancient kitten she is.
 

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