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Jeep 4.0 high idle when warm... driving me crazy
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<blockquote data-quote="NotMatt" data-source="post: 1471491" data-attributes="member: 15947"><p>Ok, so I finally got things all buttoned up on my Jeep and have been able to take it out and do some hot laps, very exciting. However, I'm having one major problem that it never did before I tore it all apart... once the thing warms up and the ECU goes into closed loop, it idles at 1500 rpm. </p><p></p><p>It's a 91 wrangler with 4.0 high output, 5 speed. </p><p></p><p>I've checked over and over for vacuum leaks... unhooked and plugged everything except the MAP sensor and FPR, no change. Took the throttle body apart and cleaned the IAC really well, tried a different IAC I had, no change. </p><p></p><p>What's my next step here? Coolant temp sensor? What range should I be looking for when it's warmed up fully? MAP sensor? What else can cause a high idle like this?</p><p></p><p>[EDIT]... Here's a loop to ponder... I swapped an earlier RENIX cherokee exhaust manifold on in place of the factory HO exhaust manifold, because it's outlet was better for my exhaust setup. Everything seemed to line up fine and the installation went well, but now I'm second-guessing myself. I eye-balled both manifolds before the swap, and didn't have to modify the earlier one at all to make it fit, it was a bolt-in kind of deal... but is there possibly a way for air to get in between the intake manifold and the head with the older exhaust manifold that I overlooked when I did the swap?</p></blockquote><p></p>
[QUOTE="NotMatt, post: 1471491, member: 15947"] Ok, so I finally got things all buttoned up on my Jeep and have been able to take it out and do some hot laps, very exciting. However, I'm having one major problem that it never did before I tore it all apart... once the thing warms up and the ECU goes into closed loop, it idles at 1500 rpm. It's a 91 wrangler with 4.0 high output, 5 speed. I've checked over and over for vacuum leaks... unhooked and plugged everything except the MAP sensor and FPR, no change. Took the throttle body apart and cleaned the IAC really well, tried a different IAC I had, no change. What's my next step here? Coolant temp sensor? What range should I be looking for when it's warmed up fully? MAP sensor? What else can cause a high idle like this? [EDIT]... Here's a loop to ponder... I swapped an earlier RENIX cherokee exhaust manifold on in place of the factory HO exhaust manifold, because it's outlet was better for my exhaust setup. Everything seemed to line up fine and the installation went well, but now I'm second-guessing myself. I eye-balled both manifolds before the swap, and didn't have to modify the earlier one at all to make it fit, it was a bolt-in kind of deal... but is there possibly a way for air to get in between the intake manifold and the head with the older exhaust manifold that I overlooked when I did the swap? [/QUOTE]
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