Shakes when I press on the gas?

Tiny
CHEVY__88
  • MEMBER
  • 2001 LINCOLN TOWN CAR
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 160,000 MILES
Had crack dead front of the intake manifold. Ordered aftermarket dorman manifold. Replaced it, while following instructions. Everything turn on ok. But now the car runs really rough and shakes when I press on the gas. Acts like it's about to die and then starts shaking until I let off the gas pedal. Also runs rough with either ac/ heater on. Also noted a Sound like a hissing, sucking noise. Near the intake on the passenger side. Possible vacuum leak?
Sunday, September 7th, 2025 AT 1:14 PM

9 Replies

Tiny
CANNON1349
  • MECHANIC
  • 862 POSTS
Hello, it is very much possible that there is a vacuum leak. It is important to make sure all of the hoses were reconnected and did not become injured during the repair. Also make sure that the new intake manifold had a new gasket on it. To test for vacuum leaks, I like to spray starting fluid around the mating surfaces of where the hissing sound is. The engine will respond to the fluid with a fluctuation in RPM.

William
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Sunday, September 7th, 2025 AT 4:32 PM
Tiny
CHEVY__88
  • MEMBER
  • 102 POSTS
It has the individual gaskets on each opening. Its not like the original and have a long gasket. I don't believe I broke anything, but never know. Spark plugs are a few years old, coils same age as spark plugs.
I did however have to replace a few o-rings on fuel injectors when I pulled off the fuel rail, some came out of the railing system.
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Sunday, September 7th, 2025 AT 4:42 PM
Tiny
CANNON1349
  • MECHANIC
  • 862 POSTS
Thanks for the reply. Were you able to track down the injector o-rings that fell out? If you double stacked the o-rings that will cause an issue, as well as not having a good seating. Please try out the vacuum leak test and let us know what you find.

William
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Sunday, September 7th, 2025 AT 5:00 PM
Tiny
CHEVY__88
  • MEMBER
  • 102 POSTS
Yes I was able to find the old o rings and only had to replace the top rings. But I sure will try out the test and let you know. Thanks
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Sunday, September 7th, 2025 AT 5:06 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,137 POSTS
Yep, also there is a main vacuum line at the rear of the manifold that I would double check. Here is a video to help you find the leak.

https://www.youtube.com/watch?v=LRKWV4Are5c

Let us know how it goes
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Tuesday, September 9th, 2025 AT 8:44 AM
Tiny
CHEVY__88
  • MEMBER
  • 102 POSTS
Thanks, ill try the spray first since it's a little cheaper and then buy the smoke machine, since im not a daily mechanic and probably wont use it much. Code reader states I have 4 open circuit fuel injector and a P1151 code.
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Tuesday, September 9th, 2025 AT 9:50 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,137 POSTS
So, this means you may have a bad fuel injector or the wiring or connector is bad at the injector so I would check that as well. If you use carb spray be careful because it is flammable. Thew smoke machine is $70.00 on amazon.
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Tuesday, September 9th, 2025 AT 4:58 PM
Tiny
CHEVY__88
  • MEMBER
  • 102 POSTS
Replaced all 8 injectors and runs fine for now. No codes or noises like before. Thanks guys.
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Tuesday, September 16th, 2025 AT 5:50 AM
Tiny
CANNON1349
  • MECHANIC
  • 862 POSTS
Good to hear! Please let us know if anything comes up, and feel free to use the website anytime.

William
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Tuesday, September 16th, 2025 AT 5:52 AM

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