100 Series Hot-Soak Hard Start / Flooding

[kwyama]

Hey all,
I’m chasing a weird hot-soak starting issue on my 100-series (2UZ-FE, ~420k miles) and wanted to sanity-check my diagnosis before I start throwing parts at it.
Symptoms:

• Cold starts: perfect
• Immediate hot restarts (shut off and restart right away): perfect
• Hot-soak restarts (30 minutes to ~2 hours after shutdown): takes 2–3 cranks to start
• Strong fuel smell when it finally starts
• Issue is intermittent
• Once running, it drives normally

Recent work:

• Injectors were ultrasonically cleaned and flow-tested ~3,500 miles ago
• New injector O-rings installed at that time
• Problem started only after the injector service (was not present before)

Diagnostics I’ve done:

• Tried Toyota “clear flood” mode (pedal to the floor during cranking) during a hot-soak no-start:
  
  • Engine starts more easily on the second crank
  • Flares up to ~5k RPM briefly
• No CEL or EVAP codes
• Cold and immediate hot starts are consistently normal

Questions:

Has anyone seen injectors start leaking after cleaning on high-mileage 2UZs?

If so, did you replace one injector or end up doing the full set?

If I do replace the fuel injectors is it best to go with OEM (expensive) or can I go with cheaper options (like taking them off a car I found with 125k miles).

Thanks for any advice.

 

[abuck99]

AI suggests that cleaning high mileage older injectors can reveal other underlying issues with worn injectors, solenoids, spray pattern etc. Chances are the cleaning did more harm than good.

If you haven’t changed your FPR, that’s a good thing to do if it’s OG, also if your fuel pump is original- it should be replaced- +200k miles, +20years it’s efficiency has diminished.

AI response to Injectors: YMMV (it’s AI)

“Short answer: yes, it can introduce new drivability issues — but not because cleaning is harmful. It’s usually because the injectors were already worn, and cleaning exposes the underlying problems.

Here’s the clearer breakdown.

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Why cleaning high‑mileage injectors sometimes causes new issues

1. Cleaning removes deposits that were “masking” wear

On very old injectors, carbon and varnish buildup can actually seal tiny internal leaks or compensate for worn pintles.
When cleaning removes that buildup, the injector may start:

• Dribbling fuel
• Having poor spray pattern
• Flowing unevenly
• Sticking intermittently


So the engine may run worse afterward — not because of the cleaning, but because the injector was already failing.

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2. Weak injectors may fail completely after cleaning

High-mileage injectors sometimes have:

• Weak internal springs
• Worn pintle caps
• Cracked plastic bodies
• Failing solenoids


A cleaning machine can stress them enough that they stop working reliably.

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3. Cleaning can reveal other engine issues

If the engine was running rich/lean due to dirty injectors, the ECU may have adapted over time.
Once injectors are cleaned and flow correctly, the engine may suddenly show:

• Vacuum leaks
• Weak ignition components
• Bad O₂ sensors
• Low fuel pressure


These issues were always there — they just weren’t obvious until fueling was corrected.

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4. Poor-quality cleaning methods can cause problems

This is less common, but possible:

• Harsh chemicals damaging seals
• Improper ultrasonic cleaning cracking plastic tips
• On-car cleaning pushing debris into injector screens


A proper shop with the right equipment avoids this.

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When cleaning helps vs. when replacement is smarter

Injector Condition Cleaning Helps Replacement Recommended
Mild deposits, normal wear
Uneven flow but no mechanical damage
Very high mileage (150k–250k+) Maybe Often
Cracked pintle caps or leaking bodies
Weak or failing solenoids
Engine misfires that return after cleaning


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AI Summary-

Cleaning is a good first step, but high‑mileage injectors are often near the end of their life. If cleaning makes things worse, it’s usually a sign the injectors were already failing internally.

If you want, tell me:

• The vehicle
• Mileage
• Symptoms before and after cleaning”