98 4.0 Idle problem - Jeep Wrangler Forum
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Old 11-13-2015, 01:50 AM
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98 4.0 Idle problem

My 98 wrangler 4.0 failed to start. By that I mean it would crank just fine, but not start. Trying again later, I depressed the accelerator pedal and it fired up, but would not idle unless throttle was open. I removed the Idle Air Control and watched it while the ignition was turned to the start position. IAC did not move. I cleaned it with spray cleaner and a toothbrush and still no movement. I purchased a new one and noticed that it was in a retracted position compared to the old one, which would allow air to bypass the throttle plate. When I installed the new one the engine fired right up but idles at 2000 rpm. Removing it and turning on the ignition revealed that it also does not move. So I am thinking whatever signals the IAC is not working. When the ignition is turned on both will buzz a bit, bot no noticeable movement. Any Ideas?????

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Old 11-13-2015, 07:11 AM   #2
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What controls the iac stepper motor is the PCM

Try a battery disconnect PCM reset and see if that helps

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Old 11-13-2015, 11:05 AM
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I never thought of a reset. However I was considering a bad ground, thinking it was getting the voltage but a bad ground was preventing it from functioning, thus the buzzing when the ignition switch is on. I'll give it a try and let you know. Thanks for the reply BB
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Old 11-13-2015, 02:54 PM
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OK I seem to have it solved. I disconnected the battery and cleaned all of the grounds both on the engine and firewall. When I plugged the IAC in and turned on the ignition, it moved completely out. For every ones information this ruined the IAC as it moved pass the intended extent of its travel. Lucky I had bought a new one. So if you want to test it make sure it is installed in the throttle body, this is what limits its travel. So either the grounds or the PCM reset solved my issue.
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