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Discussion Starter · #1 ·
97 Wrangler TJ, 2.5 engine.



Since I bought it, it has an issue with the rpm not being stable at idle. When it's cold it is worse and you can hear the engine interrupting. Even when the engine is warm, in 1st gear on Low Gear, if left to crawl at idle it will buck forwards following the rpm variation. At higher speeds, there was a strange vacuum sound coming from the engine bay, the sound would change tone when pressing/lifting off the gas pedal.



It had 1 error code to the O2 sensors. Replaced both O2 sensors, spark plugs, ignition wires, distributor, IAC.



The engine is running smoother but still I have the issue. Countless mechanics tried diagnosing it without success. No error codes show up.



A smart mechanic tried to cover the air intake and surprise, the engine kept running. This can only mean it is getting air from a second source. From what I read around here, the TJ has a issue with the exhaust manifold which can crack allowing air to get into the engine. It is in the shop right now, first thing tomorrow morning they will try to see if it is a gasket or the manifold itself.



Are there any other known weak spots which could allow "false" air to get into the engine?
 

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97 Wrangler TJ, 2.5 engine.



Since I bought it, it has an issue with the rpm not being stable at idle. When it's cold it is worse and you can hear the engine interrupting. Even when the engine is warm, in 1st gear on Low Gear, if left to crawl at idle it will buck forwards following the rpm variation. At higher speeds, there was a strange vacuum sound coming from the engine bay, the sound would change tone when pressing/lifting off the gas pedal.



It had 1 error code to the O2 sensors. Replaced both O2 sensors, spark plugs, ignition wires, distributor, IAC.



The engine is running smoother but still I have the issue. Countless mechanics tried diagnosing it without success. No error codes show up.



A smart mechanic tried to cover the air intake and surprise, the engine kept running. This can only mean it is getting air from a second source. From what I read around here, the TJ has a issue with the exhaust manifold which can crack allowing air to get into the engine. It is in the shop right now, first thing tomorrow morning they will try to see if it is a gasket or the manifold itself.



Are there any other known weak spots which could allow "false" air to get into the engine?
a cracked exhaust manifold is not going to cause the erratic idle you are dealing with (just gonna sound crappy), a bad intake/exhaust or throttle body gasket can as will a bad vacuum line.
 
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My throttle body had a significant leak where the throttle linkage attaches to the butterfly (opposite of the TPS).
 

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Discussion Starter · #7 ·
..........
Fair point :) I did not get a chance to fix it yet as I sold my daily driver and now this is the daily. Until I get a new daily driver I cannot afford to leave this in the shop for weeks. Once it's taken apart, parts can be sourced anything between 2-4 weeks here in Europe.



I will get back to this topic once I sort it out. I hope it will help other with similar issues.
 
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