Hello all, I bring you this information I compiled myself from Celica service manuals and personal experience after struggling to fix a random misfire and multiple cylinder misfire on my own Celica. *I am not responsible for any damage or injury that may occur as a result of this post.*


7th Generation Toyota Celica GT-S (1999-2006) [ZZ231] {2ZZ-GE} Misfire Guide



Check the air filter. Remove the top to your airbox housing and see how the air filter looks. If it is dirty and has dark deposits, it should be replaced.

Check for vacuum leaks. Run engine at idle. Spray brake cleaner around the intake manifold, air box, etc. If idle changes upon spraying brake cleaner, you have found your leak.

Check spark plug gap. Disconnect battery, unclip ignition coils from harness, and unbolt ignition coils from mounting point. Use ⅝” or 16mm deep socket to remove spark plug. Use gap gauge to read gap, which should be 1.1mm or 0.043”. While they’re out, make sure the spark plugs don’t look damaged.

Check resistance/pressure of each of the following with a multimeter. Proper specs are listed below. “Cold” is considered 14-122 degrees and “hot” is considered 122-212 degrees.

Ignition Coils
Run engine at idle. Disconnect fuel injectors one by one. Note which (if any) doesn’t make the idle fall when disconnected. If idle doesn’t fall when injector is disconnected, this means that the coil on that cylinder may be faulty.
Fuel Injectors
 13.4-14.2 ohms
MAF Sensor
 Cold: 2.2t-2.69k ohms
Hot: 0.49-0.67k ohms
Camshaft Sensor
 Cold: 835-1400 ohms
Hot: 1060-1645 ohms
Crankshaft Sensor
 Cold: 1630-2740 ohms
Hot: 2065-3225 ohms
Oxygen Sensors
 Upstream: 11-16 ohms
Downstream: 11-16 ohms
Fuel Pump
 Pressure: 44-50 PSI
Resistance: 0.2-3.0 ohms

Check engine compression. You can buy a kit or pay someone to have it done, but this should be the last resort, as it will cost you money beyond parts. Remember that compression from one cylinder to another should differ by only plus or minus 10%. A great difference in compression between cylinders likely signals a larger, more expensive issue.

Remember that a misfire isn't always caused by the typical culprits (spark plugs, coils, etc). There are a variety of common and uncommon causes including --but not limited-- to those components listed above. My issue ended up being an ungrounded crankshaft position sensor (pic below LOL). I also ended up replacing my spark plugs, coils, and injectors as my Celica recently surpassed 200k miles.

Let me know what you think and if there is anything to add. Good luck!
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