Engine stumbles only in no load circumstances. Idles smoothly, and stumbles only in no

More information please. I am assuming this is a Toyota. What year is this vehicle? What model is this vehicle? I am also assuming this is the 1.8 litre, four cylinder engine. The most common firing order on a 4 cylinder engine is 1, 3, 4, 2.
Does this engine idle smoothly when in Neutral and in Park? When in Park/Neutral gently press and hold the gas pedal at a slightly higher engine speed. You don't need to scream the engine just push it up to its normal working speed. Does it still run smoothly? If the engine idles and runs smoothly it suggests that it isn't the firing order causing the issue.
Do you have this problem when you select Drive or when you are actually moving? Your best option here is to take the vehicle to a good mechanic that way they will be able to see, hear and feel the vibration. This will help work out what the problem is.

There's no code that says, "#3 spark plug" but there is a code P0303 which indicates a misfire has been detected on cylinder #3. That misfire could be due to a spark plug, but it could also be a bad spark plug wire or CoP, a bad fuel injector, bad injector wiring, burnt valve, etc. Changing the spark plugs and wires would likely be the easiest and one of least expensive places to start, especially if the truck is due for a tune up anyway, but if that doesn't fix it, consider the fuel injector next. Just because it idles fine does not mean that the spark is strong at higher engine speeds.

You might also want to clean your MAF sensor and check the linearity of your throttle position sensor (TPS) to make sure the stumble is not due to a bad spot in the TPS.

It can be issue with IAC( idle air control valve) causing the problem.

There are many other possibilities causing these idle issues. Engine idles rough.

There are few help links with solutions to troubleshoot such idle issues.

I suggest you refer the link below and follow its troubleshooting details:------

Click the link below:-----

Ford Expedition IAC valve replacing

http://technoanswers.blogspot.com/2012/12/ford-expedition-iac-valve-replacing.html

Bad miss at idle?

http://technoanswers.blogspot.com/2012/01/bad-miss-at-idle.html

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Stumbling and stalling at idle after engine rebuild?

http://schematicsdiagram.blogspot.in/2012/03/stumbling-and-stalling-at-idle-after.html

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1999 Ford F-150 Idles rough and quits when gas pedal is pressed less?

http://technoanswers.blogspot.in/2012/01/1999-ford-f-150-idles-rough-and-quits.html

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Engine stumbles coming off idle when warm?

http://repairhelpcenter.blogspot.com/2012/01/engine-stumbles-coming-off-idle-when.html

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Erratic idle on car?

http://schematicsdiagram.blogspot.com/2011/12/erratic-idle-on-car.html

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Cold start problem and vehicle shudder around 2500 to 3500 rpms

http://repairhelpcenter.blogspot.com/2012/10/cold-start-problem-and-vehicle-shudder.html

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Low idle when cold out side?

http://repairhelpcenter.blogspot.com/2011/12/low-idle-when-cold-out-side.html

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GMC Sonoma Stalls and idles low

http://technoanswers.blogspot.com/2012/10/gmc-sonoma-stalls-and-idles-low.html

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GMC Idle Air Control (IAC) Valve Replacing?

http://schematicsdiagram.blogspot.com/2011/12/gmc-idle-air-control-iac-valve.html

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1996 Camry intermittent engine failure while idle?

http://repairhelpcenter.blogspot.com/2011/10/1996-camry-intermittent-engine-failure.html

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Engine quits at idle?

http://repairhelpcenter.blogspot.com/2011/10/engine-quits-at-idle.html

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Car overheats and Air blows hot at idle?

http://howtobyme.blogspot.com/2011/11/car-overheats-and-air-blows-hot-at-idle.html

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High Idle Problem

http://repairhelpcenter.blogspot.com/2012/10/high-idle-problem.html

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While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

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Idle flair is noticed on car? Rough idle? car will not idle? Erratic idle speed?

http://technoanswers.blogspot.in/2012/02/idle-flair-is-noticed-on-car-rough-idle.html

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High rpm in neutral? Inconsistant high RPM in neutral?

http://technoanswers.blogspot.in/2012/02/high-rpm-in-neutral-inconsistant-high.html

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Vehicle stumbling at idle and shows code 54?

http://schematicsdiagram.blogspot.in/2012/03/vehicle-stumbling-at-idle-and-shows.html

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Rough idle, staling and Erratic shifting?

http://technoanswers.blogspot.in/2012/03/rough-idlestaling-and-erratic-shifting.html

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While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

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These details will help.

Thanks.

Some makers used Vacuum releases for their emergency brakes which had a Vacuum switch connected to the shift assembly. This would account for a stumble if Vacuum vented out through this switch.

More common for shifting stumble to occur from Park to Drive, engaging a load on the engine, not to stumble to a freewheeling Park position. Sounds like idle speed control is sluggish to stabilize the motor.

You also have idle speed control problem with A/C, kind of shows that A/C was what kept the engine running because when you turned the A/C off, the car died.

I am going to give you some Websites for wiring diagrams. Alldatadiy.com amd Autozone.com with free wiring info upon registering your vehicle.

It seems that the base Idle speed control is not working and the A/C idle speed control is.

Also check for Vacuum leaks on the intake manifold by spraying water from a pumpbottle on the seams of the gaskets.

Check ignition Relay or ignition switch for random cutouts. The fusebox layout is on the Autozone site.

I hope my solution helps.

Since you changed the sensor we will assume it is working. When you disconnect it you put the computer in limp mode which stops it from using sensor values. If code 300 is the only code we will assume the coolant temp sensor and others are ok.
I would check fuel pressure with a gauge next.

Clean the mass air flow meter.

Check idle air control motor and passages.

While driving, the Idle air control valve (IAC) fully retracts and you control airflow with the gas pedal. When you come to a stop the computer extends the IAC to let air bypass the throttle plate and maintain idle speed. If the IAC is sticking it sometimes cannot compensate fast enough to avoid a stall. The problem is aggravated by the Air conditioner clutch cycling on while stopping. You don't mention the check engine light so not likely a sensor. If you have a OBDII scanner with live data available you can check the Throttle position sensor easily. You are looking for a smooth change through the range as you press and release the gas pedal. Or use a voltmeter to see the TPS. Measure resistance with engine off or voltage (0 to 5 volts) with ignition on. It should move smoothly through the range.
Another easy test. Park brake on, in gear (if an automatic transmission) at idle, load the engine by turning the steering quickly to the end and see how quickly the IAC recovers. Clean or replace IAC and while in there clean the carbon off of the edges of the throttle plate.

Did you check earth connection of electric system?

junked car