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Rough idle when warm

Tiny
DENISELOVE
  • MEMBER
  • 1997 CADILLAC DEVILLE
  • 4.6L
  • V8
  • TURBO
  • FWD
  • AUTOMATIC
  • 189,000 MILES
Shakes bad when warm. Replaced water pump, coil packs, spark plugs and wires, intake manifold gaskets, catalytic converter, air and gas filter, PCV, upgraded PCM, battery, starter, cleaned TB, and sensor, replaced four 02s, and did a smoke test for vacuum lines
The idle is fine when cold, but as soon as it warms up that is when the car begins to shakes like it is about to shut down. Mechanics cannot find the problem. Please advise. I am at a complete loss.

Denise
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Sunday, September 25th, 2016 AT 5:33 AM

6 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Scan for codes and check for a vacuum leak. It may be a broken motor mount as well. If it has a p0300-306 code have it freeze framed to check sensors.
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Sunday, September 25th, 2016 AT 8:22 AM
Tiny
RENEE L
  • ADMIN
  • 1,260 POSTS
Hi Denise,

If you decide you would like to conduct the scan yourself here is a link to an article that features written step by step instructions and pictures explaining how to do the scan yourself, also I have included a link to our YouTube channel with a how to video on code scanning. Most scanners are inexpensive to purchase, you can purchase one online from sites like Amazon.com

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

https://youtu.be/YV3TRZwer8k

Once you have the codes please get back to us so that we can further assist you. We are always happy to help.

Thank you for visiting 2CarPros.com.

Kindest regards,

Renee
Admin
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Sunday, September 25th, 2016 AT 4:40 PM
Tiny
DENISELOVE
  • MEMBER
  • 3 POSTS
Thank you for your help!

I have a scan tool the code is p0300. I checked all the spark plugs, coil packs, wires, fuel injector/ rail, fuel pressure all checked out good.
I do need a motor mount. But I am not understanding everything was working fine until the water pump was installed.
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Sunday, September 25th, 2016 AT 4:52 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
It may be coincidental or you may have a head gasket problem which would put more pressure on cooling system so head gasket may have blown. Have a mechanic freeze frame it to see if there is a sensor or injector bad.
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Monday, September 26th, 2016 AT 6:47 AM
Tiny
DENISELOVE
  • MEMBER
  • 3 POSTS
I pulled the electrical plug on the injectors it was a change in all cylinders except for cylinder 8 it stayed at a steady pace
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Monday, September 26th, 2016 AT 10:00 AM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Check the injector for ohms, I think it's like 11-17 if out of that range then it may be a bad injector and check compression as well.
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Monday, September 26th, 2016 AT 12:07 PM

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