Higher idle then normal.

[Dutch Rutter]

I said the magic words out loud the other day. "Truck is running GREAT!"

So naturally, this week I've noticed the idle in drive and with a warm engine is about 300-400 RPM higher then normal. Before I had it at 600-700, now its around 900-1000.
Normally, I would be thinking a small Vacuum leak somewhere, which I have not ruled out yet.

But could this also be a symptom of bad gas or a sticky choke?

Last tank of gas I had put into it was non-ethanol premium from a small local gas station. That was about two weeks ago. Now I'm less then 1/2 tank. I highly doubt they use too much of that in ground tank.

Or is there a way I can check to make sure the choke is fully disengaging?
Carburetor is a Edelbrock 1405 with the electric choke added to it.

Or should I just replacing vacuum lines?

Thanks!

 

[Craig 85]

I had a similar problem with my '79 K15 just before I sold it a few years ago. Total stock and smogged engine. My problem was the factory intake was warped right near the #8 cylinder causing a vacuum leak. I my case we determined extra heat from the EGR passage had probably caused this.

 

[Dutch Rutter]

I had a similar problem with my '79 K15 just before I sold it a few years ago. Total stock and smogged engine. My problem was the factory intake was warped right near the #8 cylinder causing a vacuum leak. I my case we determined extra heat from the EGR passage had probably caused this.

That does not bode too well for me. This has an aluminum edelbrock RPM performer on it (not new, but not beat). But the thought of a warped intake hits home a little. I noticed the intake above cylinder 1 is blacked by something, where as the rest is still clean-ish aluminum.

I'll pull out the wd-40 and hose things down. Before I do anything else. Best case its peace of mind.

 

[Dutch Rutter]

I think I found it. And boy is it a dumb problem.

The foam I have under the PCV to help keep oil from being pulled into the carb was actually pulled into the PCV and was keeping it from closing.

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I'll see how it does tomorrow.

 

[Dutch Rutter]

Doesent seem as though that was the only problem. Still had a high idle this morning. Ill stop by the Napa and grab some WD-40 for leak testing and some new vac line just to replace all the old lines anyway.

I disconnected the power from the choke and that didn't seem to effect anything, I verified the choke is not sticking closed. So choke is ruled out.

Does anyone happen to know the line sizes that runs from the rear of the carb to the brake booster, and the lines that run from the carb front ports to the heater controls, transmission converter lockup thing, and from the carb to the dizzy?

I figure if I don't find any leaks, and all the lines are new. But the high idle stays consistent, there is no harm in giving the idle screw a little turn to bring it back down where it should be right?

 

[DoubleDingo]

I had this happen, and it turned out to be excessive play in the throttle shaft. It was fine when cold, but would get stuck when up to operating temperature, and the throttle plates would keep it stuck open a little, which in turn caused a big vacuum leak on the driver's side of the base plate. When I got it to go back to normal position the idle went back down to normal. Mine is the factory quadrajet, so it was well worn. I rebuilt the carburetor a few years ago but didn't do the throttle bushings at the time. Wish I had, as it would've been fine.

 

[AuroraGirl]

Doesent seem as though that was the only problem. Still had a high idle this morning. Ill stop by the Napa and grab some WD-40 for leak testing and some new vac line just to replace all the old lines anyway.

I disconnected the power from the choke and that didn't seem to effect anything, I verified the choke is not sticking closed. So choke is ruled out.

Does anyone happen to know the line sizes that runs from the rear of the carb to the brake booster, and the lines that run from the carb front ports to the heater controls, transmission converter lockup thing, and from the carb to the dizzy?

I figure if I don't find any leaks, and all the lines are new. But the high idle stays consistent, there is no harm in giving the idle screw a little turn to bring it back down where it should be right?

uh... you may not want to keep foam down there, i see it just getting saturated with oil and thus too much pressure. or if you must use a system.. get baffles for your valve cover.. if you must use the foam, get a small screen or wire to block the opening

 

[Dutch Rutter]

uh... you may not want to keep foam down there, i see it just getting saturated with oil and thus too much pressure. or if you must use a system.. get baffles for your valve cover.. if you must use the foam, get a small screen or wire to block the opening

Good idea on the screen! I've pulled that foam out, don't plan on putting it back after it got caught up like that. The tall covers are baffled, and I even have baffled style rubber bushings for the PCV so I'm thinking I should not have much oil build up without that junk in there.

If it does, I might end up getting fancy and add an oil catch can in line between the carb and PCV.

 

[AuroraGirl]

Good idea on the screen! I've pulled that foam out, don't plan on putting it back after it got caught up like that. The tall covers are baffled, and I even have baffled style rubber bushings for the PCV so I'm thinking I should not have much oil build up without that junk in there.

If it does, I might end up getting fancy and add an oil catch can in line between the carb and PCV.

I think you dont have to worry about it unless you see a lot of wear on your rings, cylinder washing, or you got an engine that can turn high RPM before oil consumption through it becomed a problem