High idle on my 87 TBI 454

[Jim85IROC]

my truck was sitting for, well, a long time. For the last 11 months it sat at a mechanic's because it wouldn't run. It turned out to be a gas tank full of water. The year prior to that, it probably only got driven a few times.

I finally got it back out of Mechanic Jail, but driving it home I quickly discovered that it idles at what sounds like 2,000 rpm, and the throttle is very sticky.

The sticky throttle I'm attributing to the throttle cable or the pedal. The throttle linkage at the throttle body itself works nicely. The high idle is something else though... I've confirmed that at idle the throttle blades are completely closed. As far as I can see, all that leaves is the IAC. I'm guessing it froze from lack of use.

Anybody care to confirm/deny my diagnosis?

Lastly, the IAC bolts are not budging. That IAC has probably never been off the throttle body before, and I'm sure that there's plenty of galvanic corrosion. Anybody have advice for getting these out without breaking them off in the throttle body?

[Mr.Chevy4x4]

The 454 TBI motors were prone to having the gasket under the throttle body crack and get pulled in underneath. This would be the first thing I checked. It could be causing both of your problems.

Mike

[Jim85IROC]

Good to know. Can I check this with the old "spray the carb cleaner" trick, or do I need to yank the throttle body to inspect the gasket?

[Mr.Chevy4x4]

I would just pull the 3 bolts out of the TB and lift it enough to look. You shouldn't have to disconnect everything.

[kelsfine69]

Very common problem. Even look down past the injectors and I bet you will see gasket hanking in there.

[Jim85IROC]

Update:

I took a quick look around last night and found that the vacuum line that goes to the charcoal cannister was disconnected from the elbow that attaches it to the throttle body. I plugged it back in, restarted the truck, and it idles at a much lower rpm now. I'm still not convinced that it's idling quite as low as it should, but I can't be sure until I get time to throw my scan tool on it to monitor the rpm.

Now the only real issue is the throttle actuation... it's very notchy, and hard to modulate smoothly. I need to spend some time with it to figure out if it's the throttle cable or the throttle body itself. I've had this problem on my TPI cars before, and in those cases, it was the throttle body itself, not the cable, but they can be tricky to figure out, because with the car not running the throttle body will work nice and smooth, but then with it running, it gets very notchy. The airflow going past those blades has a big impact on it's behavior. But... the throttle body seems to feel ok even with the truck running, so this time I'm thinking it's more likely the cable.