shakes when I press on the gas?

2001 LINCOLN TOWN CAR
160,000 MILES • 4.6L • V8 • 2WD • AUTOMATIC
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CHEVY__88
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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?
Sep 7, 2025 at 1:14 PM
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CANNON1349
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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
Sep 7, 2025 at 4:32 PM
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CHEVY__88
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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.
Sep 7, 2025 at 4:42 PM
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CANNON1349
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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
Sep 7, 2025 at 5:00 PM
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CHEVY__88
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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
Sep 7, 2025 at 5:06 PM
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STRAILER
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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
Sep 9, 2025 at 8:44 AM
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CHEVY__88
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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.
Sep 9, 2025 at 9:50 AM
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STRAILER
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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.
Sep 9, 2025 at 4:58 PM
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CHEVY__88
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Replaced all 8 injectors and runs fine for now. No codes or noises like before. Thanks guys.
Sep 16, 2025 at 5:50 AM
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CANNON1349
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Good to hear! Please let us know if anything comes up, and feel free to use the website anytime.

William
Sep 16, 2025 at 5:52 AM