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2000 Jeep 2.5L RPM Increases and Erratic When Clutch Engages

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Hi all! I really need some help here. My husband and I are at our wits end. We have a new to us 2000 jeep wrangler, 2.5 manual. Since August when we purchased it we have only been able to drive it maybe 20-25 times. Everytime we have fixed/replaced something on it another problem comes up. So with that being said here's the newest of problems:  We have an engine code p0505. Idle air control valve.

We have cleaned the throttle body multiple times. Along with the iac sensor.  We have replaced the iac sensor 3x with mopar sensors.  At idle the engine reads 1000-1200 rpms. While driving the jeep, the rpm is where it's supposed to be.  As soon as the clutch is engaged or in neutral the rpm goes all over the place between 700-2000 rpm until we are at a complete stop. Once stopped the rpms sit at 1000-1200 rpms again. Any ideas or suggestions? We're really at a loss here. 

What we've done:.

All hoses have been checked, replaced if needed. O2 sensors replaced with NTK sensors. TPS replaced, crankshaft sensor replaced with mopar.  IAC replaced 3x with mopar.  Still getting the p0505 code and crazy/high/erratic rpm. Help please!

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  • Moses Ludel changed the title to 2.5L RPM Increases and Erratic When Clutch Engages
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Hi, Kdambrosio...Sounds like too much resistance in the wiring circuit, causing a false voltage signal.  I would carefully disconnect the plugs to the PCM.  Look for black oxidation.  Use an electronic spray cleaner and not anything hard or abrasive to clean the contacts.  Use dielectric grease to maintained a good seal when installing the connectors.  Do not condemn the PCM just yet.  If you need to go down that path, consider having your unit serviced rather than stepping up for a new PCM.

Check the grounds in the circuits.  This is ground to engine, ground to battery, ground to body.  You may be losing ground when the engine rocks on its mounts or shifts the engine to body/sheet metal ground.  Make sure there is not excessive resistance in any ground circuit, grounds are just as important as the "hot" or positive leads.   Any resistance will throw off the sensor voltage readings to the IAC.  Take voltage readings at the IAC connector.  By now, I am guessing you have a factory shop manual (FSM) for your Jeep.  If not, get a CD or reprint version without great expense.  (See eBay for manuals.)  Follow the specifications and test procedures found in the FSM.

If you discover that the IAC wiring circuit is receiving a bad voltage signal, find the source.  Check for open wires, leaks to ground, a poor ground or any kind of wire defect that will increase resistance—or even a defective ignition switch.  Also check the alternator output, alternator ground and stability.  Check the ignition distributor/coil voltage and grounds.  Be sure the distributor clamp is secure. 

Be sure the engine's spark is adequate at the distributor leads and spark plugs.  An engine will stumble under load if the spark is inadequate.  Of course, inadequate fuel supply or low fuel pressure can make the engine want to stumble under load.  The IAC would try to compensate and cause fluctuations in rpm.  Check the fuel pressure and volume/flow at the EFI fuel rail's test port.  Pressure and fuel volume/flow are equally important.

Questioning the PCM would be the last item on the checklist due to its replacement or repair cost.  They do fail, however.  You did not mention the mileage on this engine and the vehicle.  That would help determine the wear factors.

Let us know what you find.  We can go from there.



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  • Moses Ludel changed the title to 2000 Jeep 2.5L RPM Increases and Erratic When Clutch Engages

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