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Q: No idle after ignition, unless holding the throttle.

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My 99 WJ 4.0 will not stay running. I had an ignition coil bank b code come up. I replaced the coil with a BWD coil and autolite single platinum plugs. Now the truck will not relearn its idle. Since replacing above mentioned, I have replaced the IAC valve, TPS, new battery and load tested the alternator. Before this issue I replace the CPS and CKS, 3 months prior and the cat, post o2 and muffler, a month ago.

Before this issue happened, my WJ would run rough / hesitate at idle, once the engine was hot, but ran fine while giving it throttle.

Here's exactly what's happening now.

The WJ will crank and fire normally now, but will die out with no throttle after 5 - 10 seconds. While holding the throttle after ignition, the WJ will run smooth for about 20 seconds, then it will run rough. Every now and then on a start up, either the gas gauge or the volt gauge will drop down to nothing, but is not consistent.

Where do I go next?

My car has an automatic transmission.

Hi there. I can see how you’re stuck; as this one is tricky to diagnose. There are three things I would do first before removing anything else. First, download all OBD-II codes with a professional digital scanner; perhaps they will show an electrical fault with the TPS or other fuel system component. Second, check for any vacuum leaks. Although in many cases a vacuum leak will cause a high idle, it can also create similar symptoms you’re indicating. Third, when was the last time you cleaned the fuel injectors or throttle body? It’s possible that this is also a possible cause. Try these three things and if you still can’t resolve the problem, contact a local mechanic to assist you.

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