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98 TJ power loss & rough idle soon after startup

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!

Reply to
PaulT
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Reply to
L.W.(ßill) Hughes III

Thanks Bill. I had a go at getting the fault code per that link, but got nothing. I guess I am in that 6 month period. I'll have a look at replacing the crank position sensor anyway.

I'm curious though - what kind of a problem with that sensor would cause this intermittent problem?

Reply to
PaulT

Intermittent usually means a dirty connection. These computer sensors only use very low power so the slightest bit of oxidization interferes.

You can use a good contact cleaner for electronics on the pins and socket to clean them and then a ring of dielectric grease on the rubber seal on the plug to help keep more corrosion out.

The CPS is especially noted for that because the plug for it sits right on top of the exhaust manifold so gets heat and cold shocked all the time.

The TPS and other sensors plugged into the throttle body also get dirty easy, so I clean and grease them all while I am at it.

In a pinch, WD40 is a fairly decent contact cleaner, but the real stuff is better.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

PaulT wrote:

Reply to
Mike Romain

Reply to
L.W.(ßill) Hughes III

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