Arrowstorm

Well, the 307 in my 85 Custom Cruiser has been running rough for a while now, but it's still driveable.

Until today! I literally stopped at a gas station to get a drink, and then, upon turning into a busy road, I gunned the car and immediately noticed that it was running worse AND idling super high!

I drove it home and looked to see if I had a hose that was knocked off of something, but to no avail! The car seems like it is stuck in high idle and I'm not really sure what to look for to get it to idle down.

Any suggestions? Ideas? thanks,

Buz

m371961

Choke not opening properly.

joe_padavano

The possible causes are:

1) The choke is not opening properly, which could be due to a bad choke coil or a broken hot air tube to the coil

2) The fast idle cam is sticking due to crud. The cam simply drops from gravity once the choke opens and crud between the cam and the shaft can cause it to stick

3) The throttle cable is bad and sticking. This happens as the sheath wears and the steel cable strands inside start to fray. I've had this happen on two different vehicles.

4) There is interference with the throttle linkage. I've actually had this happen on one of my 307 motors where the large engine electrical harness that runs next to the carb got pushed out of position and prevented the throttle from closing properly.

You need to check all of these to find the problem.

Arrowstorm

Choke is wide open.

Throttle cable appears to be just fine.

I will check the fast idle cam, though. Never even heard of that before today. PLENTY of crud around that engine. From what I've read and what you've said, it could definitely be the culprit and I will check it out tomorrow! Thanks!

Arrowstorm

The car is idling so high that I can let my foot off the brakes from a dead stop and reach 3rd gear without touching the gas pedal.

There is nothing interfering with the linkage. In fact, parked and with the hood open, I can push the throttle completely forward until it touches the idle adjustment screw and the engine is till racing!

I've found the fast idle cam, too, but I can't really tell what it's supposed to be doing. I can move the little lever back and forth, freely without any kind of resistance and that makes no difference.

Choke is, of course, wide open.

When I first started it up this morning, it didn't run like that. In fact, it wouldn't even stay running. It would die when I slowed down. But then, when the engine warmed up after a little while it started really racing. Towards the end of the cruise, it was racing so high, when I switched gears, it was like the tranny wanted to jump out of the engine compartment!

Help! Any other ideas?

Buz

oldcutlass

Have you looked down inside the carb to note the butterfly vs throttle lever position?

Arrowstorm

i'm not sure what you mean. the top plates next to the choke are closed and aren't opening. to be honest, I'm too afraid to look down the carb with the engine racing that high, but last time I did look, the front throttle plates looked ok.

ThePackRat

Could the timing have gotten disturbed in any way ?.

Is the bolt on the distributor tight ?.

joe_padavano

Those are the secondary air valves. The secondary throttle plates are on the bottom of the carb. If they are not closing fully, the engine will race, even if the air valves are closed (the air valves do not completely seal to the air horn). If the engine is racing, shut it off without touching the throttle. NOW hold open the air valves and look down inside the secondaries. The throttle plates MUST be completely closed.

455man

Vacuum leak maybe?

turbobill

I have a 307 in an '89 Custom Cruiser with the same problem. Very fast idle when warm and runs rough (skips) and acts very lean when cold. The previous owner threw a lot of money at it trying to fix it.


Turns out that the intake gasket is leaking along the tops of the intake runners. (vacuum leak)

Professur

When looking down the carb to check the position of the plates, use a small mirror. Never put your face directly over the throats of a running motor. Small 2" mirrors with LED lights and extension cost a lot less than a glass eye and skin grafts. It's the sort of cheap inspection tool that should already be part of your basic tool kit just for the weekly walk around every driver should habitually do.