Help! Can't get it to idle after rebuild. - Ford Truck Enthusiasts Forums



1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

Help! Can't get it to idle after rebuild.

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Old 07-12-2017, 03:16 PM
jstuller jstuller is online now
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Cool Help! Can't get it to idle after rebuild.

Welcome to my nightmare.

1987 Ford 2 wheel drive, 4.9L 3 spd. w/overdrive. Stepside. (handsome truck)

I hired a guy to rebuild the motor in my garage. He took everything apart and disappeared.

I hired another guy to complete the job. He did a wonderful job of picking up someone else's mess and put it back together handsomely. (I took the head and block to a machine shop to have them make sure the essentials were correct...)

The truck starts right up, but won't idle. He couldn't figure it out. I've had other people look at it and checked the internet. I've replaced the usual suspects, (map sensor, throttle body, idle control valve, replaced the gasket on the EGR valve, ignition control module. I believe I have sprayed everything looking for vacuum leak.

Suggestions?

Signed

Befuzzled
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Old 07-12-2017, 03:37 PM
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sandymane sandymane is offline
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Quick question that may help with answers. Does the truck run down the road if you help the accelerator? Will it stay running with you giving it gas or is it just the idle you have the issue with? Sandy
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Old 07-12-2017, 05:18 PM
jstuller jstuller is online now
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Thank you for the question.

Just took it for a drive. At idle in 1st gear, it goes 18 mph. Give it gas, it takes off.

Shift to second, runs fine. Give it gas, it accelerates.

Hope that gives you clues
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Old 07-12-2017, 05:22 PM
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High idle

I should have stated: The problem is a really HIGH idle.

I don't have a tach, so I can't tell how high it is, but first gear takes me to 18 mph, and it feels like it's rearing to go.
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Old 07-12-2017, 05:45 PM
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Quote:
Originally Posted by jstuller View Post
I should have stated: The problem is a really HIGH idle. .
Thanks.. that is a very important detail because for most people a "won't idle" condition would be interpreted as a very low rpm and stalling condition.

A High idle condition is most likely a vacuum leak, either one of the intake gaskets is displaced or there has been an error or omission made with reassembly of the vacuum, EGR, or emissions components.
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Old 07-12-2017, 05:47 PM
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Sandy just went through this scenario....

High idle RPM indicates a vacuum leak.

He has a recent thread with tons of info and pointers on where to look.

and what Paul said above.
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Old 07-12-2017, 06:00 PM
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That's what I thought.

I had a BMW dealership mechanic over yesterday. He told me it was the throttle body spring not giving enough tension, so I replaced throttle body today.

I ran the EEC self-test codes just a minute ago and no codes showed up... not even a check engine light.

I will pull the intake and EGR & tube tomorrow.

Thanks
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Old 07-12-2017, 06:09 PM
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That's is probably your best bet.

Another quick test is to remove all of the vacuum lines from the vacuum tree (manifold). Run a dedicated line to the MAP sensor. Cap the remaining open port. Start the engine, if the idle is still high, you have a vacuum leak on the engine.
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Old 07-12-2017, 08:03 PM
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Quote:
Originally Posted by jstuller View Post
...I've replaced the usual suspects, (map sensor, throttle body, idle control valve, replaced the gasket on the EGR valve, ignition control module...
You're on your second replacement throttle body?

Are all the other replacement parts Motorcraft?

Did you save the old ones?

Quote:
Originally Posted by jstuller View Post
.... so I replaced throttle body today.

I ran the EEC self-test codes just a minute ago and no codes showed up...
Did you get a 11 pass code?
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Old 07-12-2017, 11:39 PM
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I only replaced the throttle body once.

I went this morning to the junkyard and pulled three and chose one that was really tight out of a 95. (same part 87-96). It is a Motorcraft.

No codes at all. The check engine light never came on.

You guys gave great ideas.

I will try them tomorrow and let you know.
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Old 07-12-2017, 11:58 PM
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The post above yours is from an experienced member that can help you a lot as can others. Let him know if you got the 11 pass code so he can help you. Just trying to help another Texan. Sandy
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Old 07-13-2017, 06:56 AM
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you have to run codes to see if you get a all clear code. then you will know there are no codes present. do you have a code reader, if not get one if your going to keep the truck for a while.

have you tried to set the idle and how. there is a specific procedure. where is the timing set with the spout out.

Last edited by Redark1; 07-15-2017 at 09:54 AM. Reason: addin
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Old 07-13-2017, 07:26 AM
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What ever you do, don't clean the TB blades. That can create the very problem you are trying to solve.

Do as Randy suggests. Dedicated vac line to MAP sensor (and I add one to the fuel regulator as well)

Replacing a bunch of parts with non motorcraft ones can often stack problems. I particularly don't trust aftermarket IACs, I'd rather clean a used stock one if you don't buy a new Motorcraft one

The aftermarket ICMs are all not made with Ford's blessing.

The only aftermarket MAP I bought failed in under a year.
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Old 07-13-2017, 07:50 AM
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Quote:
Originally Posted by Redark1 View Post
have you tried to set the idle and how. there is a specific procedure.
That procedure assumes there is no vacuum leak(s). For the most part if you do jack with the throttle stop screw, that's what it is...not an idle screw, it's to ensure the throttle blades do not fully close. This is done to prevent them from sticking in the bore.

Ford added some holes in the throttle blades at some point, which over time has proven to be a problem when the throttle bore/blades wear and allow too much air in when at closed throttle, which causes a high idle.

We could spend hours focusing on the throttle body, but there are many other problematic areas to investigate on these engine, especially the inline 6. They seem to be the most susceptible to this problem.

Some basic troubleshooting will eliminate an outside influence (rusted vacuum reservoir, broken vacuum lines, brake booster, etc.) or confirm it's on the engine.

EDIT: David was so kind to add adding a dedicated vacuum line to the fuel pressure regulator. Good call!
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Old 07-13-2017, 08:40 AM
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Oops, I can't take credit for that RLA. Scndin deserves that

But as was stated earlier, you need to plug the vacuum tee on the intake manifold. Only run a dedicated line for the FPR, the MAP.

​​​​​​That includes plugging off or blocking the PCV valve line. The PCV valve is a Metered vacuum leak.

You have to eliminate all outside lines going to numerous other controls to pinpoint a vacuum leak.
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