Rough idle help
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Freshman User
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Rough idle help
Will give the full story. Truck died last Nov and sat till July as needed a distributor. When we got it going idle was rough but it smoothes out as it warms up. It starts and runs fine for 2-3 seconds then start struggling tach drops almost to 0 then bounces back up to 1000-1200. After 60 secs it idles ok but if I drive it it feels not as powerful. Up hills it struggles a bit and is getting maybe 6-7 miles per gallon. One thing I noticed is when I turn the heat on it goes back to crappy idle like the xtra draw is messing with it. No CEL and no codes I bought the reader and nothing unless Im doing it wrong but seems pretty str8 forward. It's a really clean rust free F250 with a 351 5 speed about 120k so looking to restore it more once running issues are settled. I swapped in a ICV and a TPS as had spare and nothing. If anyone had similar issues with a fix lmk
Cargo Master
Joined: Jun 2013
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From: Somewhere n North America
How are you doing with this?
You will need to make some routine checks.
Check your Fuel Pressure & Timing.
Check/Clean your EGR Valve.
Check/Replace the vacuum line to your MAP Sensor.
You will need to make some routine checks.
Check your Fuel Pressure & Timing.
Check/Clean your EGR Valve.
Check/Replace the vacuum line to your MAP Sensor.
Fleet Owner
Joined: Oct 2005
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From: Kentucky
The output is a variable frequency square wave. Measuring with a DVM set to DC voltage will always result in a ~2.5 volt reading since the square wave has a 50% duty cycle. VREF is roughly 5 VDC therefore you are measuring one half of that value.
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Ok thanks I did read that last night so it's probably fine then. Did run codes again and getting 10 and 11 which is good the reader is working just no fault codes.
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Fleet Owner
Joined: Oct 2005
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From: Kentucky
There is no Code 10. Some code readers interpret the separator flash between the KOEO test results and Stored Code (CM) display as "Code 10".
I assume you are getting System Pass Code 11 for both the KOEO tests and Stored Code display?
I assume you are getting System Pass Code 11 for both the KOEO tests and Stored Code display?
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Yes the book says code 10 means completion of the KOEO self test and not a fault code. Just took it for a drive and has a slight stumble but what is odd is when I put the heater fan on it gets worse and stumbles more. Checked the alternator and battery those are both fine. Maybe a ground somewhere is bad?
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Ok ran the code reader a few more times Im 100% doing it correctly now and getting code 33 for the EGR valve. I also noticed the vacuum line looks like it has a metal bb in it. Its the green line with a black rubber piece on the end. the BBis in the black piece so blocking vac. Can someone look in this line see if that should be there. 5.8 351 1990 F250 Doesn't look right why have a BB in there.
Fleet Owner
Joined: Oct 2005
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From: Kentucky
There should not be a BB in that vacuum line. It is there in an attempt to keep the EGR from opening. Code 33 indicates the EGR valve is never opening.
If the EGR Valve Regulator (EVR) is leaking then it can allow vacuum to the EGR when there is not supposed to be any.
If the EGR Valve Regulator (EVR) is leaking then it can allow vacuum to the EGR when there is not supposed to be any.
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Pulled it out and code is gone but truck still runs like ****. Need to test fuel pressure so getting a gauge to check that next. EGR seems fine holds vac perfectly and voltage will rise when I add vac to it.
Cargo Master
Joined: Jun 2013
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From: Somewhere n North America
Edited; That's right.
Last edited by vjsimone; Aug 31, 2017 at 12:39 PM. Reason: Correcting Text.
Cargo Master
Joined: Jun 2013
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From: Somewhere n North America
A question to answer is; Does the EGR Valve leak Exhaust Gases into the intake during Idle and Deceleration.