'78 CIS: trouble & more trouble

[Lee]

My '78 began acting up a month or so back...it would idle high at start up, then settle back in. That behavior was then replaced by the idle hunting. It got very bad, and I began to wonder if I had a vacuum leak. I found a couple of suspiciously loose clamp screws on those rubber boots that are between the airbox and the intake manifold pipes, and tightened them. That helped for a minute, and then it began again.

I was futzing with the AAR today (whichs seems fine) and found that one of the intake manifold nuts (#6) had worked its way completely off. Very strange. I replaced it, and all seemed well. I tweeked the co mixture just a bit, because it seemed lean.

I drove it for a mile or so, and all hell started breaking loose. The idle dropped to under five hundred, the pop-off sounded like someone was working on a speed bag, and I kept getting backfire exhaust.

It does okay when the throttle is down and the revs up, but the second I let off the throttle, it goes back to this bad thing.

I might add that from time to time, it doesn't want to start, cold or hot, and I have to lift the sensor plate and flood a little gas in to get it going.

I'm feeling just a bit overwhelmed...I've gone over a lot of threads, but can't seem to find a similar situation.

Any suggestions are greatly appreciated.

Daniel Crockett

[Lee]

Oh...I need to add that I sprayed a bit of carb cleaner under the airbox, and the engine picked up pace. But I don't think the air box is damaged...at least I can't see any damage.

Thanks

[stormcrow]

Could still be a lean mixture. A lean mixture will cause "hunting" and backfiring. The other thing I would look at is your cat converter. If it is plugged or partially broken up, it will cause problems with backfiring.

To test your system properly, you need a fuel pressure gauge to see exactly what's happening with the system.

Steve

"A Porsche does more then just go fast in a straight line"