I'm having a problem with my '98 Wrangler, I6, manual transmission:
Within 2 or 3 minutes of starting up, it develops a significant power loss at speed, and at rest it idles very roughly at approx. 200 or 300 RPM. If I attempt to rev it up while this is happening, it hesitates and backfires. If I just let it sit idling, it will sort itself out after a couple of minutes (though occasionally it is bad enough that it stalls). Alternatively, if I turn the engine off then restart it, the problem goes away immediately (occasionally, it comes back, but not as bad and a second restart cures it). This happens regardless of the weather/temperature or the engine temperature, though it's often not as bad if the engine is already warm.
I recently gave it a service (oil, oil filter, plugs, and air filter changed) - this had no effect on the problem.
Has anyone seen and solved a problem like this before? Any suggestions?
Thanks!