High Idle on 328

Make sure the aux air valve is not stuck open first. If it is not, then you can adjust the idle off the big brass nut on the intake plenum/throttle body.

 

Two other possibilities:

The old floor mat pressing against the throttle
or


weak throttle return springs

I almost have that mythical need nothing Ferrari except I ONLY need new return springs- they are hard to find and are on back order. Anyone know where to get them?

Dan

 

also check to see that the accel pedal cable is not frayed and hanging.

try working it with your hand from engine end.

 

Your induction system may be sucking air someplace. My 77 GTB had a manifold leak next to the head that caused that same symptom. Idle was ok until it warmed up and then it went to 2000 RPM. It was cause by the previous owner running the wrong coolant which caused corrosion. I fixed it by having my intakes welded to add material and then milled back to spec. Labor and machining came to about $400.

Bob Wassam

 

This sounds very similar to the problem I have with my car. Although my tach is not working properly, I remember what 2k RPM sounds like from my previous 328's when they were going through their cold weather start-up program. My current car ('88.5 328) gets warmed up from driving and will idle at roughly 2k RPM. This is most noticeable when coming to a stoplight. The car actually will cruise in second gear with no throttle input after it's warmed up and I can feel the car pushing forward until I pop it in neutral coming to a stop. I already tried adjusting the idle by the plenu and it's already bottomed out. Would this require the same fix?

 

I had a 328, there is all kinds of crap that can cause it.

the two issues I had was that aux air valve under the header tank was
sticking open from cold. (the car wouldn't idle down from cold very well)
you can check that by squeezing that air hose to the intake closed
(i can't remember which hose but you'll know it when you look at the
plumbing)

the other one was a vacuum leak... used carb cleaner to find it.
it came from the brake vacuum circuit.. very weird.

I'd check the simple stuff first, like someone else said. cable hangin up or
binding, etc.

but any air not being metered by the injection system can cause a high
idle (like that aux by pass circuit). may be vacuum line is screwed up or something.

 

Thanks! I'll look into those.