Engine surge?

Tiny
AUTOSAVOYNOT
  • MEMBER
  • 2000 GMC SONOMA
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 115,000 MILES
My Sonoma's engine will rev a couple times when slowing down. It usually happens when it slows to about 20 mpg or less. Sometimes when I drive slow then put it in park it will idle faster than normal. But if I shut it off then restart it, it will idle normal. The check engine light just came on today but it's been doing this for a while. It seems to shift fine when accellorating, the trans doesn't slip. I've had trans service done, a tune up & a new fuel filter & my gas mileage still fluxuates up & down. Does this sound like an O2 sensor or throttle sensor? I've put way too much money into many repairs on a weekly basis. Can you help me?
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Tuesday, June 24th, 2008 AT 5:34 PM

5 Replies

Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
Could be o2 or coolant sensor or Mass Airflow Meter doing that.Need to start by having the PCM scanned for codes, that is why the check engine light is on.The stored code/codes will most likely lead to the fix for your car or at least give a general direction to go in

Check out this guide it can help

https://www.2carpros.com/articles/engine-surges

Please run down this guide and report back.
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Wednesday, June 25th, 2008 AT 7:40 AM
Tiny
TAL55LYD
  • MEMBER
  • 1 POST
  • 1995 GMC SONOMA
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 167,892 MILES
Throttle body motor, surges, shoots gas heavy then light Thur injectors serv # 16197427 ECU ven# 1gtcs19z1s8506889 put 2 diffidence ECU makes no change please help thanks Tim
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Wednesday, December 2nd, 2020 AT 9:20 AM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
If it surges, check the gasket below the throttle body, they loved to break and cause vacuum leaks. Also check the vacuum hose to the map sensor as well as the one going to the pcv valve. They get soft and will leak and cause all kinds of problems.
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Wednesday, December 2nd, 2020 AT 9:20 AM (Merged)
Tiny
BEAVERWELCH
  • MEMBER
  • 1 POST
  • 1993 GMC SONOMA
  • 2.4L
  • V6
  • 2WD
  • MANUAL
  • 120,000 MILES
Engine surges while idling or running down the the road. Has new wires plugs rotor cap rotor button no vacuum leaks. New manifold temperature sensor valve. Fuel is clean, have changed the fuel filter twice.
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Wednesday, December 2nd, 2020 AT 9:20 AM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,554 POSTS
Hey BEAVERWELCH

This sounds like a classic MAP sensor problem. This guide can help as well

https://www.2carpros.com/articles/engine-surges

Check out the diagrams below to show you on your car. Check out the diagrams (Below). Please let us know what happens.
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Wednesday, December 2nd, 2020 AT 9:20 AM (Merged)

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