# 97 f250 with 5.8 funny idle



## Kwise (Sep 24, 2009)

My 97 f250 5.8 heavy duty sometimes idles funny. It does not idle rough, but rather the rpm fluctuates up and down. It only does this in reverse or drive, while at a standstill or moving very slowly. When I put it in neutral or park, it idles fine. I suspect the egr valve. Has anyone had this problem?


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## Milwaukee (Dec 28, 2007)

Are you use motorcraft dist cap, rotor, and spark plugs? That what cause my F250 run like that.


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## Kwise (Sep 24, 2009)

I think so. If they aren't, how would that affect it? It's only been doing this for a few months.


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## PatriotLawnCare (Oct 4, 2009)

First check obvious stuff. Make sure your cap and rotor are in decent shape, make sure your plug wires are actually plugged in correctly. I bought a 95 once that supposedly had bad engine troubles and only needed a tune up and a tps. Look underneath and see if the plumbing for the EGR valve has rusted out or separated. I've seen a couple of these that the tubing for it has rusted and then broke causing a bad reading on the sensor. Have you pulled the codes? Not all diagnostic codes will throw a check engine light. They may point you in the right direction. Good luck


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## Milwaukee (Dec 28, 2007)

Kwise;1009486 said:


> I think so. If they aren't, how would that affect it? It's only been doing this for a few months.


 not use motorcraft parts can cause this issues. It no fun when you found that auto zone's dist cap and spark plug wires are garbage and cause short out.


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## affekonig (Aug 5, 2008)

Idle air control valve


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## FordFisherman (Dec 5, 2007)

I thought the IACV was a 5.4 problem? I just replaced mine; truck sounded like a foghorn. To the OP- check that your vacuum lines are not cracked/disconnected also.


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## affekonig (Aug 5, 2008)

I've had the same issue on a few 5.8s and it always worked for me if I remember correctly.


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## hydro_37 (Sep 10, 2006)

Sounds like a vacuum leak


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## tuna (Nov 2, 2002)

IAC or TPS most likley IAC.


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## blk90s13 (Sep 1, 2005)

spray carburetor cleaner at your throttle body and see how it reacts that gasket is known to go bad I changed mine and cleaned the throttle body and it was running like a champ even since 

( I owned a 95 f-250 5.8l 4 years ago )


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## rpainetfd (Jan 9, 2009)

I have the same truck and had the same problem this winter. I EEC tested it and had a code for EGR excessive flow. Found the EGR valve to be sticking open just a little and the map sensor compensating. If you unplug the vaccum line to the map (black sensor on the firewall with one vaccum line) you can verify this. You can also verify this while it is acting up if you spray carb cleaner in the valve, it should smooth out. Mine was acting up in the middle of a storm and didnt have the time to change it. I held the plunger open with a screwdriver and sprayed it wtih carb cleaner. Than I ran some fuel injection cleaner through the tank. It fixed it 90%. Sometime between now and October I might change the valve. Good luck.


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## Kwise (Sep 24, 2009)

My mechanic suggested the IAC valve. I changed it out and it fixed it the problem...most of the time. It still acts funny sometimes but I think the IAC was bad. The EGR and all the obvious stuff looks ok. I'm content for now. Thanks for the advice everyone.


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