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What causes a rough idle

Tiny
SHAWNZZZ
  • MEMBER
  • 1998 CHEVROLET VENTURE
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 120,000 MILES
What could cause the motor to rough idle besides the coil packs and plugs/wires?
Wednesday, June 30th, 2010 AT 4:47 PM

12 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Do you have a check engine light and when was your last major tune-up?

The following below could cause it

1. Defective spark plug
2. Inadequate spark/coil, defective spark plug wire.
3. Lack of compression
4. False air leakage.
5. Faulty fuel injectors.
6. Insufficient fuel pressure.
7. Contaminated fuel.
8. EGR valve that is leaking.
9. Oxygen sensors.
10. Throttle position sensor.
11. Idle air control valve.
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Wednesday, June 30th, 2010 AT 6:01 PM
Tiny
JIG MASTER
  • MEMBER
  • 4 POSTS
Check for intake leaks. Chevy is very bad on intake leaks about 100,000. Look for anti-freeze leaking around the lower intake, if it gets into the engine it will trash it! If you are good there than do a complete throttle body clean to see if this helps. You will need to remove it to clean it properly. Dirty fuel injectors will cause this too! Check your plugs and see how they are burning should be light tan in color around the electrode porcelain.
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Tuesday, September 25th, 2018 AT 7:43 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,665 POSTS
Great addition to this thread! Please feel free to help out whenever you are on the site. :)

Cheers, Ken
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Thursday, September 27th, 2018 AT 11:27 AM
Tiny
CHRISW1979
  • MEMBER
  • 1 POST
  • 1998 CHEVROLET VENTURE
  • 3.4L
  • V6
  • FWD
  • AUTOMATIC
  • 150,000 MILES
Hello, I recently replaced the intake, valve cover, and throttle body gaskets and now the vehicle has a low idle but it starts and runs fine only problem is with the idle and help please its my handicapped mom's van and really need to get it back up and running right
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Thursday, September 27th, 2018 AT 11:27 AM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Clean throttle plate on both sides and iac hole with choke cleaner then drive where you can get above 40 mph. Then check for a vacuum leak if still low.
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Thursday, September 27th, 2018 AT 11:27 AM (Merged)
Tiny
SSTEVENSON
  • MEMBER
  • 2 POSTS
  • 1998 CHEVROLET VENTURE
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 128,000 MILES
I have a 98 Chevrolet Venture that when stopped it idles rough. When I am driving it is fine and there is no check engine light on. If you put it in neutral it runs smooth. About 2 months ago had a tune up done on it. Any ideas?
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Thursday, September 27th, 2018 AT 11:27 AM (Merged)
Tiny
LEGITIMATE007
  • MECHANIC
  • 5,121 POSTS
Yeah from what your saying it sounds like your idle air control valve is fualty or may just be dirty, lets do what is called a throttle body cleaning, making sure that the airfilter is clean and the throttle body and throttle plate along with the idle air control (iac) valve is cleaned too, before we decide we need a new one.
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Thursday, September 27th, 2018 AT 11:27 AM (Merged)
Tiny
LES
  • MEMBER
  • 2 POSTS
  • 1998 CHEVROLET VENTURE
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 132,000 MILES
My 1998 Chevy Venture van has a rough idle and it gets very hot red line hot and then would go back to normal and finally it did not have power and it showed to be all the way on red but when I stopped and checked it was not boiling or steaming. I hooked it up to a diagnostic machine and wouldn't give a read out. And I tried that on two different diagnosing machines. What direction should I take know?
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Thursday, September 27th, 2018 AT 11:27 AM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Check the thermostat and for the rough idle-Engine running rough or misfiring can be cause by the following:

1. Defective spark plug.
2. Inadequate spark/coil, defective spark plug wire.
3. Lack of compression
4. Vacuum leak
5. Fautly fuel injectors.
6. Insufficient fuel pressure.
7. Contaminated fuel.
8. EGR valve that is leaking.
9. Oxygen sensors
10. Idle air control valve
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Thursday, September 27th, 2018 AT 11:27 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
If the chek engine light isn't on, it won't show a code. As far as the issue, have you tried replacing the thermostat? Have you checked the catalytic converter to see if it is plugging?
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Thursday, September 27th, 2018 AT 11:27 AM (Merged)
Tiny
LES
  • MEMBER
  • 2 POSTS
I have already put new a thermostat an a water pump in. Is there a way to test the spark/coil pack?
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Thursday, September 27th, 2018 AT 11:27 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
The easiest thing to do is to remove one of the plugs, lay it on the engine block and have a helper crank the engine. You should be getting a hot blue snapping spark.

Let me know what you find.
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Thursday, September 27th, 2018 AT 11:27 AM (Merged)

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