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Engine Cold start RPM surge being cut short.

  • Thread starter Thread starter CTEyoungboy
  • Start date Start date Feb 10, 2025
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    #coldstart
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CTEyoungboy

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Feb 10, 2025
#1
  • Feb 10, 2025
  • #1
Village idiot here.

Context: Recently installed heater core bypass on my 90 5.0 GT

After install I have noticed that the cold start RPM surge is cut short almost immediately after hitting its highest point. No longer a smooth decline into operating idle. No other idle issues outside of cold start.

Any thoughts on what would cause that?

It was a knuckle banging job and wouldn’t be surprised if I hit something out of place. Also maybe i’m paranoid and it has nothing to do with that whatsoever? But seems to line up with that bypass repair. Preciate any help!
 

General karthief

wonder how much it would cost to ship you a pair
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#2
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How did you bypass the heater core? Pics?
 
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CTEyoungboy

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#3
  • Feb 11, 2025
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Just the standard bypass tube. I’m sure it probably needs to be trimmed but was in an autozone parking lot.

 

Noobz347

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I suspect that you knocked a vacuum line loose someplace. It may be dry/brittle/broken and difficult to find.

Pull codes!
 
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CTEyoungboy

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  • Feb 11, 2025
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Noobz347 said:
I suspect that you knocked a vacuum line loose someplace. It may be dry/brittle/broken and difficult to find.

Pull codes!
Click to expand...
Cool yea that was my initial thought fear because I busted an AC one while in there as well. Will thoroughly look into the lines.

Thanks for the input!
 
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CTEyoungboy

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Update: Checked vacuums everything seems fine visually. But car suddenly won’t start now and stinks of gasoline. Is it fair to say it may be IAC related??
 
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CTEyoungboy

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#7
  • Feb 11, 2025
  • #7
CTEyoungboy said:
Update: Checked vacuums everything seems fine visually. But car suddenly won’t start now and stinks of gasoline. Is it fair to say it may be IAC related??
Click to expand...
* it cranks strong. battery seems fine. but check engine light is on now.
 

AeroCoupe

lube between the nut and the face. I know my lubes
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#8
  • Feb 12, 2025
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Pull codes.
 
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CTEyoungboy

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  • Feb 12, 2025
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AeroCoupe said:
Pull codes.
Click to expand...
The code I got is 34.

From what I read it’s EGR related. Maybe the hose? or the entire EGR?
 

Noobz347

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CTEyoungboy said:
The code I got is 34.

From what I read it’s EGR related. Maybe the hose? or the entire EGR?
Click to expand...

Probably the EGR diaphragm and if so, yes, it would need to be replaced. It would also be a pretty good vacuum leak.
 
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CTEyoungboy

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#11
  • Feb 12, 2025
  • #11
Noobz347 said:
Probably the EGR diaphragm and if so, yes, it would need to be replaced. It would also be a pretty good vacuum leak.
Click to expand...
Could the vacuum line running from the EGR being cracked provide the same fault? or is it strictly the EGR diaphragm?

Thanks for your input!
 

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor
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#12
  • Feb 12, 2025
  • #12
CTEyoungboy said:
Could the vacuum line running from the EGR being cracked provide the same fault? or is it strictly the EGR diaphragm?

Thanks for your input!
Click to expand...

Yes, a cracked line running to the EGR should be fixed first.

Retest

Then replace EGR if necessary.
 
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CTEyoungboy

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#13
  • Feb 12, 2025
  • #13
Noobz347 said:
Yes, a cracked line running to the EGR should be fixed first.

Retest

Then replace EGR if necessary.
Click to expand...
You’re the man. Will do. Thanks again!
 
C

CTEyoungboy

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#14
  • Feb 12, 2025
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Update: After looking into the lines. it actually seems as though the EGR vacuum solenoid has a crack somewhere in it. Even light suction on the lines I can hear the noise emanating from inside it.
 
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gkomo

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#15
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I had code 34 and just replaced the entire EGR solenoid and sensor and it cleared the code.
 
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