I recently rebuilt the engine in my 98 TJ with the 4.0. New pistons, lifters, push rods, gaskets. My buddy cut the exhaust off literally right after the manifold and before the Cat. I’m faced with an idle problem. When it warms up it idles around 1500-1700 sitting, and can get up to 2000 with clutch pressed in while moving. Already replaced MAP, IAC, TPS sensors. Could it be timing? Or my exhaust?
Well, your buddy is an idiot. You are now missing 2 critical O2 sensors, which means that the computer only has a "before" reading of the effect of the cats. I'm not sure how or if this affects the air/fuel mixture, but I do know that it does nothing good at all. I'm also curious whether the upstream sensors were replaced, and if so then what brand.
You need O2 sensors and you need catalytic converters for this vehicle to run correctly. It relies on the PCM, and the PCM relies on all the sensors that the vehicle came with. Get the exhaust back together with correct parts and see how it runs then.
You need O2 sensors and you need catalytic converters for this vehicle to run correctly. It relies on the PCM, and the PCM relies on all the sensors that the vehicle came with. Get the exhaust back together with correct parts and see how it runs then.
There is indeed a problem with the O2 sensors having been removed but my bet is the high rpms are caused by a vacuum leak. Considering the work just completed my guess is the reinstallation of the intake manifold was perhaps a bit rushed leaving it imperfectly seated and imperfectly sealed to the head. That would cause a vacuum leak and thus high idle rpms. That particular vacuum leak is common after removing/replacing the intake manifold if extra care isn't taken to insure it is properly positioned over the positioning studs on the head.