'97 Wrangler Cold Idle / Load Flooding Problem - Jeep Wrangler Forum
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Old 12-18-2009, 06:28 AM   #1
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Exclamation '97 Wrangler Cold Idle / Load Flooding Problem

I have a '97 Jeep Wrangler SE with a 2.5L (I4) Fuel Injected Engine and I've been having a flooding problem after I crank the the vehicle. It cranks very easily and like it is supposed to, but after about 7-10 seconds of running, the engine begins to flood itself very noticeably in terms of sound and exhaust smell (unburned gasoline).

At an idle with no load, tapping the throttle a few quick times will cure the flooding symptoms immediately, and afterwards the vehicle runs normally. If I start the vehicle and immediately begin driving (putting any type of load against the engine), at the exact same time the engine would flood while idling, the engine begins to flood itself very badly, oftentimes so bad it begins to stall, and may backfire. After a few seconds of the flooding / stuttering, its almost as if the engine burns all the excess gasoline at once and takes off (1.5x1000 rpms during flooding quickly double to 3.0x1000 rpms with the accelerator still depressed).

While trying to diagnose the problem with the breather off the throttle body, a very loud rush of air into the intake can be heard at the same moment the vehicle begins to flood itself during idling.

I've also noticed that the operating temperature of the engine effects how bad the problem is. If the engine is at operating temperature (~210 deg. F), shut down, and immediately restarted, the engine does not flood during idling or under a load at all. After the engine cools for at least 25 minutes or more to below 160, the flooding problem is worse during idle and under a load than any other time, even if the engine were completely cold. On the first start of a normal morning, at about an average of 50 degrees, the flooding is noticable, but not as bad as very cold mornings (32 and under) and still not as bad as if the engine is warm but not at operating temperature.

I've also noticed that rain seems to make the flooding at idle and under load worse, even though the problem is still clearly evident on dry, warm days.

Finally, i've noticed that as I continue to put more miles on my wrangler without correcting the problem, the flooding seems to be getting more intense, and my gas mileage / engine power seems to be getting progressively worse and worse.

Evidently the vehicle has already received the updated software meant to address the Recall issue where some PCM's in this year model were incapable of detecting a faulty catalytic converter. This software upgrade was completed before I bought the vehicle, and the dealer that performed the work put a sticker under the hood.

My best guess is either an issue with the MAP sensor or the Idle Air Controller. I've cleaned the IAC and surround already, but did not notice any improvement after I put it back on. I have no hardware other than basic voltage meters to be able to test the MAP sensor, but i'm not even sure if this type of test would be appropriate or helpful.

One last thing that may be related is that there is what seems to be a small vacuum pump on the drivers side of the vehicle that makes a loud racket during operation. I don't know if the pump isn't building the appropriate amount of vacuum, and I also don't know if this component is faulty or even related to the problem. The vacuum controls for my heater box and selector work just fine so i'm assuming that this is a non issue.

Any help is greatly appreciated, i'll gladly trade computer advice (i'm a CIS major at Appalachian State) for advice that helps me get the Jeep running like it used to.

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Old 12-18-2009, 11:10 PM   #2
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Betcha it's not excessive gas - flooding - but excessive air, like a vacuum leak.

You cannot use your nose to determine rich or lean, both will cause unburned gas to come out the tailpipe due to the misfiring. That's what you smell. Only an exhaust analyzer can tell. Even an ignition problem smells the same.

By ignition problem it's not always the electrical ignition system, "igniting problem" compression, rich, lean etc.

Look for a vacuum leak.
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