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I have 2004 Jeep Grand Cherokee special Edition 4.0. Idles very rough. I have changed plugs, all 4 O2 sensors.and gas filter regulator. Vehicle continues to idle rough. Vehilce show no codes. Vehicle runs great other wise. Any ideas? Please help
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Sounds like an aftermarket O2 sensor was replaced. Should not be the problem unless your check engine light is on and giving that code. Also have you looked into your erg valve?
check the O2 sensors in the exhaust manifold with a automotive meter not a code reader ,then trade it in for a diesel manual version as these are impressive but 4.7 litre gas guzler at our petrol prices about 10 dollars a gallon in the -uk and around 7/8 dollars here in spain this vehicle you couldnt give away here
The spark plugs should have been changed at 60,000
Gas filter every 3 years
Air Filter every 3 years or sooner
The MAF Sensor cleaned every year
By now the O2 Sensors are slow to respond
If they have 100,000 change the front 2 sensors
Check TPS Voltage
Check Fuel Pressure at the fuel rail
Egr Valve most likely bad
If you have COP Ignition Coils, they may be misfiring,
common ford problem
Unrelated--change trans and power steering fluids
every 3 years,never go over 30,000 miles on any vehicle
You haven't changed everything...map sensor controls spark and fuel mixture as does the throttle position sensor, also check the idle control valve...Don't just buy stuff...do testing first.
The idle air control valve (IAC) may be stuck or failing. This solenoid-type device controls the airflow into the engine at idle. It is fed control input signals from the engine's computer. Over time, the IAC valve may become dirty from EGR gases and carbon, etc. It may have a worn pintle (valve head) or the return spring may be weak or broken, causing a rough idle or even stalling from an over-rich fuel/air mixture. The second thing to have checked is the throttle position sensor.TPS. These devices will "flag" a fault on your vehicle's onboard OBD-II computer, which a decent code reader/scanner can display and clear. Third, a dirty throttle body housing/venturi can cause rough idling and poor response. A special cleaner is needed to remove oil and carbon residues from the specially-coated inner surfaces of the throttle body. Fourth; you may have a Mass Airflow Sensor (MAF) that might be failing/malfunctioning. Some vehicles use these instead of the Manifold Absolute Pressure (MAP) Sensor, which you may have. These sensors need to be checked and verified that they are functioning properly. Fifth; check/change your vehicle's fuel filter, and verify proper/adequate fuel pump pressure and flow performance. Don't run your vehicle below 1/4 tank of fuel...doing this sharply reduces the life and cooling of the in-tank electric fuel pump. These are not cheap, or easy to replace!
If you haven't changed the plugs or had the fuel system cleaned, now would be a good time to do it. The number 1 culprit for rough idles is dirty injectors or plugs. You can try an injector cleaner in a can (or bottle) for under $10 and see if it helps, and then work from there. If there isn't any improvement then if you are able to, check the plugs for any gunky buildup and if you find a bad plug, make sure you replace them all (or have them replaced) at the same time.
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