Sudden, very rought idle

[a-dougk1]

I brought the 79 930 home to the garage a couple of weeks ago after filling up at the gas station. Now, when I try to start the car, the engine will idle roughly at about 100-200 rpm. If I give it a little gas, it will hesitate, but the idle speed will go up. After about a minute, the idle will start running normally at about 900 rpm, but, if I give it a little gas, the speed will go up until I let up on the accelerator pedal, then the idle speed will go down to 100-200 rpm for about a minute again, then back to normal.

I don't really want to take the car out on the highway like that, so I was looking for suggestions where to look to fix this problem. I suppose I could have bought bad gas, but why would the idle speed go back to normal after a while, but still choke when I blip the accelerator?

I'd appreciate any advice on where to start looking for this problem. It's about time for a tune-up anyway, so I'm ready to start as soon as I have some idea where to start.

Thanks.

[bkreigsr]

sounds like you developed a vacuum leak,..... 1979? - that makes your hoses 31 years old, unless they've been replaced somewhere along the line.
just poke around the engine and intercooler looking for cracks or breaks in any hoses, you could get lucky. Bill K

[a-dougk1]

All of the vacuum hoses were replaced when I bought the car 6 years ago. It had a really serious leak which caused the engine to rev past 2000 rpm when cold. Rather than just replace the leaking hose, I replaced them all (because, as you say, they were very old).

That's not to say that it isn't leaking again. I will check this weekend to see if anything has come loose or is broken.

Any other ideas?