Mystery warm start issue
 

2002 with 170k miles. Cold start, works perfectly, and drives as normal. When I park for example to get gas, it starts back up. If I park it for longer, say to go into a store for 10+min, it won’t start. It bogs and sputters, then dies. Kind of like it’s running too rich…? Each successive start attempt is worse, then it barely turns over.

After that, I wait about 45min, then it starts back up like normal, and runs perfectly.

MPG is the same as ever (-shitty).

Tail pipe is clean, not black. No smoke or anything.

When this first started, it was occasional. But months later it’s every time.

It threw a p0171 code, but only once.

I’ve cleaned the MAF multiple times, throttle body, air filter.

Suspect peoples first guess is a vacuum leak, but this doesn’t make sense to me, because there’s some kind of temp variable, it runs fine except for the warm start.

Ideas?

Thanks.

Mine would idle roughly after restarting after 10+ minutes. Turns out it was a bad fuel injector. Tried the fuel injector cleaner from the auto parts store, but that didn't work so ended up replacing the problem one. After that, no rough idle and good fuel trims.

I'd start with the fuel system cleaner, see if that helps at all.

I’m leaning towards a leaking fuel injector that’s sticking open when hot.

However, you mentioning it barely turns over after several start attempts sounds like it’s starting to hydraulic. And no white smoke (not antifreeze) when it restarts seems like gas.

If you pull your dipstick does the oil smell like gas?


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First, start off simple. I would go through all of your vacuum hoses. Start the engine up and carefully listen for hissing sounds. Next, I would try cleaning your IAC valve. Ive never done one on a 4runner but I have many other cars with success. I cleaned one on my daughters Camry last year because of a similar problem. Ill see if I can find a link with directions on how to do it. 199963 makes a good point as well about a leaky injector.

IAC Cleaning - Easy Method???

Forgot to mention I had tried the fuel system cleaner at least once.

I’ve searched in this a lot, and found (only) one guy with the same problem, and his ended up being a bad injector, so I think you guys are on to it.

IAC also seemed close, I may just try this as well.

I’ll also listen for vacuum leaks, not sure if I’ve tried this yet. No gas smell on dipstick.

I was thinking it might be something like the coolant temp sensor, although this would be a strange failure mode (gets progressively worse) for a sensor but it does seem to check the other boxes.

You could try giving it some throttle on a hot start……


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Yes, tried various throttle inputs, all the way up to flooring it. Helps sometimes if I time it exactly right - right at ignition. Once it’s stumbling it’s over.

Mystery warm start issue
 

The fact that the more you try to restart It eventually barely turns over I think it’s hydraulicing. I doubt the battery is dead since you’re not charging it to start it later.

How fast can can you pull plugs after a failed hot start?

What is your LTFT with a hot engine driving down the road?


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I have changed the battery in the last ~6 months so good there.

I probably can’t pull the plugs all that fast…

LTFT…?

Long Term Fuel Trim. It’s the parameter that triggers to too rich or too lean code. It’s part of the live data stream.


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How would I/ the mechanic know one of the injectors is ‘intermittently’ failing? Is there specific diagnostic equip they’ll need to use?

All indications are I’m going to have to spoon feed my mechanic, and I’m not sure what this “ok” mechanic has. Even though I live in a big city, I’ve yet to find someone good to work on this old truck.

Thanks.

Resistance check all the injectors. For best results check them with the engine cold and at operating temperature. Spec is 13.8 ohms resistance at 68 degrees Fahrenheit.

Solved
 

Thanks for all of the input. I changed the coolant temp sensor, and two warm starts were normal/ as they should be. Looks like a fix!

Good stuff. I didn't know about this. Did you use a generic $9 sensor for the 3rd gen or an OEM one? I maywell have this problem, as my 1st start of the AM is great, but next warm start often dies unless I keep the R's up for a bit.




Google:

What happens when coolant temperature sensor goes bad?

A faulty ECT sensor can send a false signal to the onboard computer, resulting in an incorrect air-fuel mixture. For example, a faulty sensor can send a signal indicating the engine is cold when it is not, and more fuel will heat the engine quickly.


Edit - this is the location, right?

Yes, it sounds like you might have the same thing. It’s not a difficult part to change, you can do it in less than an hour. That said, it’s also not expensive to get an OEM one, they’re around $55 plus shipping (you’ll also need 5 crush washers). I just went with the OEM. Less than $100 to fix something two mechanics couldn’t (wouldn’t bother, really) figure out.