Choppy idle when first starting
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5th Wheeling
Joined: Jun 2024
Posts: 28
Likes: 1
Choppy idle when first starting
I have a 1989 f-250 with a 351w. When I first start it, the idle is really choppy. It sounds like it’s been cammed out, but it’s stock. After about 10 seconds, the idle goes back up and it runs normal. I gotta touch the gas a little bit when the idle is choppy because it feels like it wants to stall. Any ideas?
Logistics Pro
Joined: Nov 2013
Posts: 3,928
Likes: 1,198
From: Mojave, Ca
If suspect a leaking fuel injector. Use a fuel pressure gauge to monitor your fuel pressure. Once the system is pressurized, turn off the engine and watch the fuel pressure. It should drop about 1psi per minute.
Logistics Pro
Joined: Aug 2014
Posts: 3,558
Likes: 852
I have same issue, changed all injectors didn't make a difference.
Spark plugs good, not wet.
i think it’s EGR vacuum leak, only at cold start up.
possibly bad o2 sensor/dirty, doesn’t work cold.
ive lived with the issue 6 months.
I remember reading a post about an old/dirty O2 sensor causing the problem.
Oh, and no codes right? no stored codes?
Spark plugs good, not wet.
i think it’s EGR vacuum leak, only at cold start up.
possibly bad o2 sensor/dirty, doesn’t work cold.
ive lived with the issue 6 months.
I remember reading a post about an old/dirty O2 sensor causing the problem.
Oh, and no codes right? no stored codes?
More Turbo
Joined: Oct 2023
Posts: 607
Likes: 153
From: Canada
Ok so it fires up. Slightly weird. Then it hits high idle for 20 seconds but at about 1600 rpm. Then it goes too low and stalls out? Does it reek of fuel (rich run)
and do you have any other odd slightly odd running issues. Like a stutter here or there. Anything like that? Sounds like it could be as simple as a temp sensor. Also all the maintenance needs to be done. Like plugs and wires and fuel filter. Air filter. Pcv. And any dirty grounds or battery connectors. All the basic maintenance stuff do first. And if it's still doing weird stuff. Dig deeper. Like 02 and testing the throttle body with an analog mulit meter. Stuff like that. If you like the truck maybe upgrade to the 4 hole fuel injectors.
note and egg or fuel smells. Those matter.
and do you have any other odd slightly odd running issues. Like a stutter here or there. Anything like that? Sounds like it could be as simple as a temp sensor. Also all the maintenance needs to be done. Like plugs and wires and fuel filter. Air filter. Pcv. And any dirty grounds or battery connectors. All the basic maintenance stuff do first. And if it's still doing weird stuff. Dig deeper. Like 02 and testing the throttle body with an analog mulit meter. Stuff like that. If you like the truck maybe upgrade to the 4 hole fuel injectors.
note and egg or fuel smells. Those matter.
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5th Wheeling
Joined: Jun 2024
Posts: 28
Likes: 1
It smells like the exhaust from an old car, but not like gasoline. It starts and immediately the rpm’s drop. It’ll do between 400 and 600 and the idle is choppy like it has a big cam. The truck shakes quite a bit when it does this. Then I give a little gas and it usually goes to running normal
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More Turbo
Joined: Oct 2023
Posts: 607
Likes: 153
From: Canada
It smells like the exhaust from an old car, but not like gasoline. It starts and immediately the rpm’s drop. It’ll do between 400 and 600 and the idle is choppy like it has a big cam. The truck shakes quite a bit when it does this. Then I give a little gas and it usually goes to running normal
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More Turbo
Joined: Oct 2023
Posts: 607
Likes: 153
From: Canada
if you're lucky the parts store will have one for like 25 bucks in stock. They're not too expensive. Good luck
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
The code is for the control solenoid over on the coil bracket.. the one at the front. The vacuum source for that should be the vacuum canister on the passenger inner fender, and the output of the solenoid goes to the EGR control valve on the side of the throttlebidy.
The EGR valve should not open at all at a cold start and there should be no vacuum present in the line to the valve at idle, you should check for that
And one thing you can try is to disconect and cap the vacuum to the valve to see if that has any effect on cold start operation.
You should also test the vacuum canister(juice can looking thing) to ensure it holds a vacuum, the metal cans were prone to rusting out and were replaced with a plastic version later on.
2 more things, pull the vacuum line off the fuel pressure regulator with the engine running just to see if there is any fuel in it, there should not be.
When were the plugs and wires last changed? A miss that cures itself makes me suspect the plug wires, you can see this if the engine is run in the dark with all the lights off... anywhere the wires are comprmised will glow every time an ignition pulse passes.