3.2 rising or hunting idle

[avahdani]

Once in a whikle my Idle rises higher than normal but not always, Any suggestions, could this be Vacuum leaks, Idle Control Valve or. Throttle not fully closing?

[wazzz]

When this happens, it could be the idle switch on the throttle body that is not closing. This can be adjusted.

[proporsche]

little info for you to check ..

[avahdani]

Thanks, I'll try it

[Jeff Alton]

Throttle switch, ICV, base mixture issue or vacuum leak.... could be any of them.

Cheers

[ant7]

Also; replace the O-ring on the idle screw, this can be a source of air/vacuum leakage.
Ant.

Originally Posted by Jeff Alton

Throttle switch, ICV, base mixture issue or vacuum leak.... could be any of them.

Cheers

[brighton911]

The manifold to head gaskets are a common place for vacuum leaks. Check the torque on the hold down bolts.

[FrontGarage911]

Behind the throttle body there is a cluster of vacuum lines that degrade over time. The biggest one that you have to watch out for is the brass pipe that comes out of the throttle body boot going towards the cruise control unit. It generally fails at the reducing coupler.

[scarceller]

Already mentioned, likely the idle switch out of adjustment. Or base idle speed not properly set.

A properly working idle switch should behave as follows:
- Engine fully warm
- Should idle at 800RPM for 84-85 cars and 880RPM for 86-89
- With engine idling properly at correct speed
- If you unplug the Idle Switch, 2 pin connector on RHS of throttle body the idle speed will and must change, it usually goes up above 1000RPM the moment you unplug the switch.

So, if you are at idle and unplug the switch and nothing changes it usually means the switch is not closed and needs proper adjustment OR the switch is bad.

You can easily test the switch with a ohm meter.

To set base idle speed correctly you can email me I'd be happy to send you my own easy procedure or use the Bentley shop manual.

[scarceller]

Also a bad/failing idle control valve can also cause issues.

Here's another check I have come up with that helps sanity check idle control behavior. Follow these test steps.

- Engine dead cold, must be dead cold!
- Do not touch the gas pedal during any of this testing
- Turn key and start engine, observer behavior at startup. Does it start right up and idle at 1100RPMs? Does it hunt up/down for idle speed? it should not.
- It should start up and instantly idle at 1100-1200RPM at initial cold start
- over the next 3 minutes let it idle while watching idle speed
- the idle speed must come down without you doing anything, do not touch gas pedal just observe.
- After few minutes it should settle down to the target WARM idle speed of 880RPMs

If everything works as outlined above it means the idle switch is closed, the idle control valve works and the mixture is not far off baseline.