Engine Cold start RPM surge being cut short.

[CTEyoungboy]

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]

How did you bypass the heater core? Pics?

 

[CTEyoungboy]

Just the standard bypass tube. I’m sure it probably needs to be trimmed but was in an autozone parking lot.

 

[Noobz347]

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

Pull codes!

 

[CTEyoungboy]

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

Pull codes!

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!

 

[CTEyoungboy]

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??

 

[CTEyoungboy]

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??

* it cranks strong. battery seems fine. but check engine light is on now.

 

[AeroCoupe]

Pull codes.

 

[CTEyoungboy]

Pull codes.

The code I got is 34.

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

 

[Noobz347]

The code I got is 34.

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

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

 

[CTEyoungboy]

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

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]

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!

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

Retest

Then replace EGR if necessary.

 

[CTEyoungboy]

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

Retest

Then replace EGR if necessary.

You’re the man. Will do. Thanks again!

 

[CTEyoungboy]

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.

 

[gkomo]

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