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Old September 15th, 2013, 05:46 PM   #1
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Throttle lag. Help please!!!!

Hello, I bought my first jeep about a month ago - 1999 Cherokee Sport. I love everything about it, besides this "throttle lag" problem I've been having. Most of the time it happens when the engine is cold when I'm lightly accelerating from a stop (between 10-25 mph). The lights dim on the dash and it acts like its about to stall for about 5 seconds, and after that its fine. I've changed the plugs twice (first ones were champion copper plus, now I'm running autolite double platinums), cleaned the battery cables and ground mounts, ran fuel injector cleaner through it. I was getting a bad o2 sensor reading, but realized last night while putting in an a/c bypass pulley that one of my plug wires was bad, so I put all new plug wires in this morning. It started up a lot easier, the check engine light turned off, but it's still lagging. Can someone please help me with this? I'm still in high school, so I'm a little tight on cash and don't want to keep buying things that aren't going to fix this problem. Thanks for reading!!

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Old September 16th, 2013, 08:53 AM   #2
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Kinda sounds like IAC sensor. Try replacing that and see if it goes away. I had a 91 Xj that would try to cut out and die while the engine was cold warming up. After it warmed up it was fine but i replaced the IAC ($20ish if i remember correctly) and its easy to access. Worth a shot.
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Old September 21st, 2013, 06:55 AM   #3
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throttle lag would have nothing to do with IAC. That only effects idle and is completely neglected when you open the throttle. I would check your TPS. I'm assuming it runs fine after up to speed? Use an analog 5v meter and check for dead spots on the TPS sensor.
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Old September 21st, 2013, 06:58 AM   #4
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Ding ding!

If the tps checks out ok, I'd check the resistance values of the coolant sensor too. A cold engine that thinks it's already warm can have a lean stumble until it warms up.

Last edited by Rob the plumber; September 21st, 2013 at 07:01 AM.
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