'86 Idle "Surge"

[Redcoupe864+3]

Hi, All--

On its way to me is my honest-to-gosh First Vette, a late '86
(aluminum heads) Coupe with the much-discussed Nash 4+3. Test
drive revealed a basically nice car-- very clean, 68,000 2-owner miles.

The idle, however, simply refuses to steady out, jumping from 500
rpm to 800 or so and back again, as though I were blipping the
throttle. The car will be stored until spring or something like it arrives
here in the Northeast; any thoughts I can relay to my mechanic in
the meantime? Thanks Much!

 

[jpanek]

My idle surge was cured by cleaning and reoiling the K&N air filter. Another thought is to check the large oval snout hose that attaches to the air filter outlet/MAF/throttle body. Those can be installed incorrectly underneath at the throttle body side, giving you an unmetered vacuum leak.

 

[The Car Whisperer]

I agree with jpanek - check for an air leak anywhere between the Mass Air Flow sensor and the intake manifold. See if anything is loose or if the intake snorkel has a crack or leak. Check the hose clamps that attach it, then check the bolts at the throttle body etc. Sounds like the engine is adjusting for some extra air it's getting somewhere after the sensor measures the incoming air mass.

 

[Redcoupe864+3]

Thanks, guys. An air/vacuum leak sounds about right. Will check when
the car arrives. 'Preciate it!

 

[The Car Whisperer]

No problem, let us know what you find.

 

[corvette66]

...

other idle problems can be from the IAC (idle air control) or TPS (throttle position sensor). both sensors are attached to the throttle body housing. I had both of these sensors go bad on my grand prix, caused it to idle real bad. took a few days to figure out what it was. If you get a GM code scanner from autozone or somehwere it will pin point the idle problem for you.

good luck to you.