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My car has done more than 300,000 kms, she starts perfectly first thing in the morning.

After I leave it running for a while, it most of the times (throughout the day) takes about 5 seconds to crank before actually starting. Once started it runs fine.

Note: this happens intermittently throughout the day. But if I leave it off for say 8-9 hours, it starts fine again.

So far I have checked and cleaned:

  • Battery (good condition)

  • Alternator (normal)

  • Mass airflow sensor (cleaned)

  • Throttle body (cleaned)

  • Use high quality fuel from BP (98 octane)

  • Used best quality fuel system cleaner 3-4 times when tank was empty (to diagnose the problem)

  • Change spark plugs (installed OEM brand)

  • Recently changed oil/oil filter (to make sure I'm using correct viscosity oil)

The problem is still there.

The reason why I'm not leaning towards fuel pump / filter is because first thing in the morning it starts perfectly.

One last thing, if I stop the car and start right up within 3-4 minutes, it starts right up without any issues.

Any sensible ideas from experienced mechanics are welcome

Update: Toyota Kluger 2008 V6

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  • How do you know the fuel is high quality - 98 octane is not a quality rating, you could be buying fuel from a cheap or poor source... But I would consider an engine temperature sensor fault as a possibility.
    – Solar Mike
    Commented May 21, 2018 at 6:41
  • When asking questions like this, letting us know the make/model/year/engine of the vehicle in question helps tremendously in helping you to solve your issues. Please edit your question and include.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented May 21, 2018 at 13:53

4 Answers 4

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Ticking the boxes of ignition and basic maintenance I'd be looking at your fuel injectors. The pintles can wear out and allow fuel to bleed off into the cylinder thus dropping pressure.
This excess fuel in the cylinder can cause a flooding condition on warm start which the PCM doesn't know how to deal with since it expects fuel pressure to be there and thus won't immediately demand anything from the fuel pump. Second possibility also has to do with the injectors. When worn they can get out of resistance spec from the internal wires developing an open condition that gets exacerbated when the engine is warm thus demanding too much current to jump the gaps to fire which would also cause a warm start issue.
Basics still apply of Fuel, Air Spark and I'd guess that the injectors aren't providing the fuel or the PCM doesn't know that it doesn't have any fuel pressure and has to wait for the fuel pump to rebuild it before it will start.

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  • Welcome to Motor Vehicle Maintenance & Repair! If the injectors were bleeding off fuel as you suggest, there'd be more of a problem with cold starts then warm. Reason being, with bleeding injectors, the longer they sit, the more fuel gets dumped into the cylinder (until all the pressure is bled off). The OP would see the issue more on the cold side than on the warm. Also, there shouldn't be any "gaps to fire" in the injectors. If there are, they wouldn't fire at all. Injectors have solenoid windings which are a complete circuit. If open, they don't work at all, warm or cold.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Sep 7, 2018 at 10:49
  • @Pᴀᴜʟsᴛᴇʀ2 "more of a problem with cold starts then warm" you have a reasonable theory, do you have any more evidence? Don't feel like leak can be ruled out. It still seems possible to me that the volume of fuel leaked may be small enough not to flood, but large enough to starve the next few injection cycles it, causing a slow start, especially if the reduced rail pressure allows the fuel in the rail to vaporize. (I have similar but less severe symptoms on a 1URFE with 250k miles. Slower restart on hot days when left in the sun. Suspect slow injector leak.)
    – nmr
    Commented Jul 6 at 15:54
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    The reason for harder starts when cold is there is more time for fuel to drain from a leaking injector, thus more fuel in the cylinder causing a flooding condition. When there is a shorter time between restarts, there's less time for leakage to occur, and thus less of a chance of flooding.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Jul 6 at 16:26
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I've seen this type of behaviour caused by fuel vaporisation. This is where fuel system components or supply lines are routed close to hot components and not adequately shielded. This can cause fuel to effectively boil in the fuel lines so when you attempt to start the vehicle, it is massively lean until the point where cool fuel pumped up from the tank reaches the fuel system.

One other thing to investigate, is the fuel system supposed to prime? Some systems will run the fuel pump for a short period when the drivers door is opened or when the key is turned to the ignition stop before being turned to crank. If this isn't happening for some reason, you may be having to wait until the fuel pump provides enough pressure at the fuel rail to start the vehicle.

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My vote is for the injectors. Had the same issue where fuel was dripping into the intake from an injector nozzle making for hard warm starts but likely evaporating away if left a long enough.

I verified by connecting a fuel pressure gauge to the rubber fuel hose supplying the rail on each bank (my car had no schrader valve). Got all components up to normal temperature by driving and then clamp off the upstream fuel supply hose and saw the pressure drop away 80% in an hour.

The theory is that the fuel pressure would have nowhere to go except through a leaking injector assuming the hoses are good also this was a return less system. I was hoping this leak test would fail on just one bank so only requiring three new injectors ... nup.

Another possibility is the coolant temperature sensor, if faulty it could be reporting the wrong temperature to the engine computer causing it to start up richer than necessary. In my case I changed out this relatively cheap sensor to no avail.

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These are classic symptoms of vapor lock due to insufficient rail pressure.

Have a look at this answer for more details on potential causes for hot start problems.

The reason why this happens only for hot starts is because the fuel is more likely to vaporize as temperature increases. In order to avoid vaporization problems the fuel lines are expected to be pressurized during a hot start.

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