My car does not idle very well. Is there a fix?


Many.  Read Michael Stegbauer's Idle page. Brad Baur has an excellent idle surge VFAQ up. Also read the answer to "How do I adjust the idle on a [DSM]" in this FAQ.

If this process doesn't work, you are in the minority. Try looking for something basic, such as

  • loose throttle cable
  • fouled spark plugs
  • defective or gunked-up idle speed control (ISC) motor
  • leaking injectors
  • cracked vacuum hose
  • damaged intake manifold gasket
  • Timing. (If you have adjustable cam gears, make sure they didn't move)

High idle can also be caused by a throttle cable or cruise control cables that are too tight.

Some troubleshooting tips: if your idle adjusts when your A/C compressor is on, or when all of the electrical accessories are on, the ISC is at least partially working. If your idle appears to fluctuate with temperature, suspect an air leak in a vacuum hose or at the air intake first.

If you need to check the ISC, do it when it is hot. The ISC resistance can sometimes change when it has cooled down. Thus, the ISC looks ok when checked, but misbehaves when actually operating. The same holds true for cables since they can tighten up during operation.

The Last Word: With the age of these cars, cracked hoses, hardened gaskets and broken seals are going to be very common. The throttle body shaft seals can leak air, for one example. It's the nature of an older car.

 

ISC
Motor

TPS

Idle
Switch

TDC
Sensor

Cable
Adjust

Idle
Adjust

ECU
(caps)

Plugs/
Wires

Reed
Sensor

Failure Rate

Medium High

Low

High

Low

Low

High

High

Medium

Low

Failure Severity

Medium

High

Low

High

Low

Low

High

Low

Low

Periodic Maintainence

N/A

N/A

Yes

N/A

Yes

Yes

Yes

Yes

N/A

Idle is low

* * * * *

*

-

* * *

-

* * *

*

*

*

Stalls during stops

* * * *

*

* * *

*

-

* *

*

*

***

Idle is high

* *

*

* * *

*

* * *

* *

*

*

* *

Car won't start

-

-

-

* * * *

-

-

* * * *

*

*

Idle is irratic

* * *

* *

*

* *

*

*

* *

* * *

* *

Stumble during idle

*

*

-

* *

*

*

*

* * * * *

*

Legend

*****Very Likely
****Likely 
***Eh... 
**Not Likely
*Very Unlikely

QA #190

Last Updated:
2016-11-24 11:40


Cam Dorland | 95 Eagle Talon
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