Surging Idle *video* - Ford Powerstroke Diesel Forum
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Old 02-26-2014, 10:23 PM
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Surging Idle *video*

I've been battling the idle on this truck for over a year now. Diagnostics have been run on it from two different sources, and neither can find anything wrong. ICP and IPR show up fine on autoenginuity, CCT scan shows up fine, compression has been tested and is well within spec, buzz test passes. Has new valve cover harness, new glow plugs and relay, new lift pump...I'm about to lose my mind. Basically, I've decided I am going to have to start throwing some parts at it and see what happens. Truck is bone stock.

Symptoms: Doesn't like to start without being plugged in under 40 degrees. The truck romps a few seconds at startup, which is not uncommon from what I have read. As it warms up, it reaches a point just after the temperature needle starts moving where it surges as shown in the video. When the truck gets to full operating temperature, it doesn't surge any more but the truck has what seems like a very slight miss. Just shakes a little bit. Sometimes worse than others.

The truck is a 1995 model with 103,000 miles. Automatic transmission. Hopefully I have covered everything.

I'm leaning toward throwing a new IPR in first. I've heard that it doesn't always test bad on the laptop. What about the EOT sensor? I've heard that it has an effect on timing. Anyone know what the symptoms of a bad EOT are?

I will accept any suggestions you can give me. And if you know anyone in the College Station, TX area that can help me, please send them my way.

http://youtu.be/MR1Qk-4DAdI
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Old 02-28-2014, 07:45 PM
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Does it do it if you start it in Neutral (vice Park)? Cheers!
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Old 03-02-2014, 10:56 PM
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It romps when I start it in neutral and park, but the romps don't feel anything like the rough idle I get at red lights and stop signs. Can the TRS cause rough idling other than during starts? I read a Ford bulletin that said romps were just a characteristic of the motor, but I'm still curious as to whether it can cause a rough idle while driving and stopping at lights as well, since it is harder to test that theory.
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Old 03-04-2014, 08:07 AM
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Whats your voltage gauge doing while its surging? Are any electronics on? Heater, or anything?
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Old 03-06-2014, 07:17 AM
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Voltage stays steady. Although sometimes when the idle drops I hear like a humming noise from under the hood. Goes away when idle comes back up. If the Alternator is bad, or the voltage regulator, would that cause a rough idle?
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Old 03-08-2014, 10:05 PM
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I have no personal experience with this, but I have read that a bad IDM can cause rough running conditions, and I would think your sensors would still be checking out ok from your PCM. ( just a guess ). Also - just an FYI, don't know how you are checking it, but a GPR cannot be checked with a test light. A bad gpr can still light up a test light and not function properly. Either ohm it out, or listen for an audible click when your turn the ignition on. No click, bad relay

Also, if you want or need to, you can always pull the valve covers off and physically check to make sure all injectors are firing. Have you checked your fuel pressure with a gauge?

Last edited by kctyphoon; 03-08-2014 at 10:13 PM.
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Old 03-09-2014, 10:39 PM
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I just borrowed an ICP sensor to see if that made a difference. Nada.

I've read about the IDM, Too. Was hoping I wouldn't have to throw parts at it just to see if they worked, but that may be the next thing to try.

I tested the GPR with my meter and it seems to be working fine. I can hear the click, too.

One thing I have noticed as that my truck tries to start a lot faster than other 7.3's I've seen. I've read that the truck isn't supposed to start until it senses enough oil pressure. Maybe somehow it is trying to start before the oil pressure builds up enough? Maybe the IPR is stuck and not allowing enough pressure to fire all the injectors?

The valve cover gaskets and wiring harness was all redone, and they changed the glow plugs and checked compression with they had the valve covers off. They checked oil flow from the injectors as well.

I'm just irritated because I bought this truck hoping it would last me a really long time with how low the mileage is. But I don't trust it to drive it a long distance because of these little things that worry me, haha.
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Old 03-10-2014, 07:49 AM
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I'm sure it's something simple. It's tough diagnosing things over the internet or through a video but i've been there and know how you feel. When this is figured out you'll never want to get rid of it.

Give the IDM a try and see what it does.
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Old 03-10-2014, 10:21 AM
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subbed... mine just started doing the same thing

I have not had much time to diagnose. However, i unplugged the outside harnesses from the valve covers and found that they were soaked and smelled like burnt electronics. I dried them the best i could and hit the valve cover side with some air to dry the plugs and it seemed to clear it up. I have no idea if this was the problem but it would be worth a look.

keep this updated. i would like to know what you find
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Old 03-12-2014, 10:42 AM
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I will do my best to keep this updated. It will be a slow process just because I don't have a lot of time to work on it. Hopefully I will get it figured out and be able to update the post with a solution.

I do have another theory pertaining to the EOT sensor. I've read that it controls fueling, timing, and how long the glowplugs are activated. So, if my EOT constantly reads a high temperature, the timing and fueling would be incorrect until it reaches whatever temperature it is showing. A new EOT can be ordered online for $18, so I may do that first since it is the cheapest. If that doesn't fix it, Next will be the IDM and the IPR.
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