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Low Idle w/ 4th cyl Misfire

 
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  #1 (permalink)  
Old 23 Dec 2016, 08:01 am
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Question Low Idle w/ 4th cyl Misfire

2005 2.4L - 124k Miles - No Mods or updates
For as long as I have owned the car it has had a rough idle, but recently it has gotten worse. the car is now idling around 100 Rpm per the Tack. it doesn't stall, just sits and shutters in park or stopped at a light. when RPMs are 500 or lower i get a 4th cylinder misfire, and it make the engine shake. it can be at cold or hot it will always start a misfire. Turning the A/C on makes the shudder worse and there is no increase in RPM. Engine Light is consistent on until the misfire then it flashes.

So far I have:

Changed Plugs - Gap .042
Changed Wires
Cleaned throttle body and sensors
Sea foam intake, oil, and fuel Clean
New IAC Valve
Checked vacuum leaks - None
Compression - Ok
Reset via battery disconnect

Last edited by Vpareker; 23 Dec 2016 at 08:20 am. Reason: added detail
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Old 23 Dec 2016, 09:25 am
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Location: Lake Wales, FL
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Default Re: Low Idle w/ 4th cyl Misfire

Have you checked for broken motor mounts?
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Old 23 Dec 2016, 01:29 pm
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Default Re: Low Idle w/ 4th cyl Misfire

Change your computer or have the dealer re-flash a new firmware version for the PCM. There have been several technical service bulletins indicating problems with rough and low idle speeds on the 2.4L engine. A updated computer will have a factory authorized update sticker under the engine hood, mine has one.
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2003 GT M/T in Onyx Green Pearl on Michelin Pilot Sport AS 3 Plus Tires 205/50ZR17. Dark Slate Gray Interior. OEM cargo net, parcel shelf, slush mats and trunk protector, mud flaps, mopar subwoofer. Platinum edition pedals, Neon SX 2.0 steering wheel with black+grey wrapped leather cover. Generic lowering springs, KYB gas shocks, Valeo solid flywheel conversion and clutch kit. Urethane insert engine mounts. Energy suspension full body urethane bushing kit. Chrysler premium front speakers, Jenson 6x9 rears. Boston Audio 4x55W amp. Panasonic head unit with xtenzi bluetooth. 300W AC power inverter. Escort 360max and Escort Shifter ZR4, dual front+rear dash camera. stage 1 blow off valve and syked tune computer . Boost and oil pressure gauges with Turbo-Timer. Needswings 3" exhaust elbow, Electric valve actuated Y-pipe with catalytic converter. To do: coilovers, 2step controller, quaife diff, Air-Fuel Meter
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Old 23 Dec 2016, 02:56 pm
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Default Re: Low Idle w/ 4th cyl Misfire

Quote:
Originally Posted by Vpareker View Post
the car is now idling around 100 Rpm per the Tack. Engine Light is consistent on until the misfire then it flashes.
only time my car idled that low was when the coil burned out and it was only running on 2 cylinders, which was east to disgnose with the trouble codes. im not saying to go buy a coil.

if the engine light is on, what are the trouble codes?

Last edited by rob302; 23 Dec 2016 at 02:58 pm.
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Old 23 Dec 2016, 03:48 pm
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Default Re: Low Idle w/ 4th cyl Misfire

Quote:
Originally Posted by Vpareker View Post
2005 2.4L - 124k Miles - No Mods or updates
For as long as I have owned the car it has had a rough idle, but recently it has gotten worse. the car is now idling around 100 Rpm per the Tack. it doesn't stall, just sits and shutters in park or stopped at a light. when RPMs are 500 or lower i get a 4th cylinder misfire, and it make the engine shake. it can be at cold or hot it will always start a misfire. Turning the A/C on makes the shudder worse and there is no increase in RPM. Engine Light is consistent on until the misfire then it flashes.

So far I have:

Changed Plugs - Gap .042
Changed Wires
Cleaned throttle body and sensors
Sea foam intake, oil, and fuel Clean
New IAC Valve
Checked vacuum leaks - None
Compression - Ok
Reset via battery disconnect
Is it 100 or 1,000 rpm?

Does both speeds on your radiator fan working properly? Try with the engine cold, start the engine, turn on the A/C and see if the radiator fan immediately comes on. If it does not I would suggest manually checking both speeds by applying 12 volts with the radiator fan plug unplugged. This will lower the rpm's at an idle.
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Last edited by ptcruisersteve; 23 Dec 2016 at 06:35 pm.
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Old 23 Dec 2016, 05:25 pm
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Default Re: Low Idle w/ 4th cyl Misfire

I have been having similar issues. Idles about 700 - 750 rpm. Sounds like a diesel. No misfire codes at all. Runs good otherwise except shifting at high rpm such as goosing it getting on the freeway, seems to lag shifting into next gear or overdrive unless letting off the throttle. 150 k and its just getting old I guess. Time for a new car. I am beginning to think its the PCM as well. some have said to get diagnostic reader and leave it plugged in to monitor things. So you did a compression check? I need to get a vacuum gage. My old one is ng. That can tell you a lot too. I pulled the big booster line off and the engine revved up so I do not see how a vacuum leak would drop idle speed. Another problem I have read on here is the gasket at the block where the intake plenum attaches is a problem that cause similar symptoms. Be nice if it threw a code at least saying sensor "?" is malfunctioned. I am thinking of changing the 02 sensors since they have never been done. Good luck finding your problem
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Old 23 Dec 2016, 07:58 pm
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Default Re: Low Idle w/ 4th cyl Misfire

Quote:
Originally Posted by L2fish View Post
I have been having similar issues. Idles about 700 - 750 rpm. Sounds like a diesel. No misfire codes at all. Runs good otherwise except shifting at high rpm such as goosing it getting on the freeway, seems to lag shifting into next gear or overdrive unless letting off the throttle. 150 k and its just getting old I guess. Time for a new car. I am beginning to think its the PCM as well. some have said to get diagnostic reader and leave it plugged in to monitor things. So you did a compression check? I need to get a vacuum gage. My old one is ng. That can tell you a lot too. I pulled the big booster line off and the engine revved up so I do not see how a vacuum leak would drop idle speed. Another problem I have read on here is the gasket at the block where the intake plenum attaches is a problem that cause similar symptoms. Be nice if it threw a code at least saying sensor "?" is malfunctioned. I am thinking of changing the 02 sensors since they have never been done. Good luck finding your problem
The target idle speed on these cars is between 700 to 750 rpm. there is no problem with the idle speed on yours. It's something else. Try pouring two quart of acetone or xylene into the gas and let it idle for 30 minutes to see if the symptoms go away.
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Old 23 Dec 2016, 08:57 pm
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Default Re: Low Idle w/ 4th cyl Misfire

Quote:
Originally Posted by _PTGT03 View Post
The target idle speed on these cars is between 700 to 750 rpm. there is no problem with the idle speed on yours. It's something else. Try pouring two quart of acetone or xylene into the gas and let it idle for 30 minutes to see if the symptoms go away.
No instructions as how fast these chemicals have to be through the system before it damages fuel related components? This is a very dangerous suggestion and should not be attempted.
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Old 23 Dec 2016, 09:28 pm
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Default Re: Low Idle w/ 4th cyl Misfire

Quote:
Originally Posted by ptcruisersteve View Post
No instructions as how fast these chemicals have to be through the system before it damages fuel related components? This is a very dangerous suggestion and should not be attempted.
respectfully, you have no idea what you're talking about.
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2003 GT M/T in Onyx Green Pearl on Michelin Pilot Sport AS 3 Plus Tires 205/50ZR17. Dark Slate Gray Interior. OEM cargo net, parcel shelf, slush mats and trunk protector, mud flaps, mopar subwoofer. Platinum edition pedals, Neon SX 2.0 steering wheel with black+grey wrapped leather cover. Generic lowering springs, KYB gas shocks, Valeo solid flywheel conversion and clutch kit. Urethane insert engine mounts. Energy suspension full body urethane bushing kit. Chrysler premium front speakers, Jenson 6x9 rears. Boston Audio 4x55W amp. Panasonic head unit with xtenzi bluetooth. 300W AC power inverter. Escort 360max and Escort Shifter ZR4, dual front+rear dash camera. stage 1 blow off valve and syked tune computer . Boost and oil pressure gauges with Turbo-Timer. Needswings 3" exhaust elbow, Electric valve actuated Y-pipe with catalytic converter. To do: coilovers, 2step controller, quaife diff, Air-Fuel Meter
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Old 23 Dec 2016, 11:48 pm
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Default Re: Low Idle w/ 4th cyl Misfire

Quote:
Originally Posted by _PTGT03 View Post
respectfully, you have no idea what you're talking about.
Using acetone is a bad idea.

Acetone is known to deteriorate cheap plastics and other substances. While the components in a car's fuel system should be of high quality, and thus immune to any deleterious effects from exposure to acetone, be aware that "ideal" is not always the case in practice. Be advised that not all systems have been tested against acetone. Until such thorough testing has been accomplished and certified by an accredited authority, you assume your own liability for experimentally testing acetone in your particular system.

As I said before I would suggest not giving out this advice anymore. It sounds like you want someone else to check out your theory and if it damages the fuel system components you will know not to try it on your own PT Cruiser.

Since you say you are an expert on this issue prove to me that testing has been accomplished and certified by an accredited authority for the PT Cruisers.

Seems to me you are violating forum rules getting other members to try out your experiments for you.
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Last edited by ptcruisersteve; 24 Dec 2016 at 12:27 am.
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