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Old 02-17-2020, 06:35 PM
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JMat JMat is offline
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Join Date: Feb 2013
Location: Reno, NV
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JMat JMat is offline
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Join Date: Feb 2013
Location: Reno, NV
Posts: 195
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New Issue has Me Stumped-Running Rough & Fuel Trim Issues

This is a relatively new issue and only happens after 100+ mile drives at highway speeds. This is a '98 3.4l auto 4x4.
After driving for for a long period at highway speeds and the car has been running great I hit the offramp and have to stop for a red light and my long term fuel trim drops to +1.56%(my usual long term fuel trim at idle is +3.12%) the engine is almost stalling and the Short Term Fuel Trim is jumping around between +18% to +20%. The light goes green, I step on the gas and the car is running fine again, no lack of power and not rough(fuel trims quickly return to "normal"). I drive it the mile home and pull in to garage, leave it in gear and the fuel trim drops back down to +1.56% and the STFT starts bouncing around -17 to -19%.(180degree flip on STFT) and after checking the exhaust it's definitely running rich.

Plugs, wires(NGK) and O2 sensors(OEM) are less than a year old and under 20k miles. MAF has been cleaned within 5k. There are no codes or pending codes either.
Any ideas on where to start? I'm at a loss.

Edit: This all goes away when i shut the car off and let it sit for 15-20 minutes
My rig has 348k miles and federal emissions.
__________________
1998 Toyota 4Runner 3.4 4x4 with 340,000 miles.
199mm TBU-Bilstein 4600-'99 Tall Springs(Rear).Almost Totally Stock

1997 Toyota 4Runner 3.4 4x4 with 247k miles-Project car

Last edited by JMat; 02-17-2020 at 07:41 PM. Reason: Added Info
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