anonymousagain

Today during mellow city driving in the '83, I stopped at a light and the idle dropped to ~400rpm.

Normally it's dead-nuts at 700rpm. There wasn't any significant "event" since the previous stop light a few blocks before. Seems to run normal while driving.

Did a vaccume line check in the parking lot, but couldn't see anything broken or in an abnormal location. ONLY noticeable wierdness is that the idle adjustment doesn't do anything...out or in drops the idle??

Any ideas?

Sailmed

A vacuum leak (minor) raises the idle..
A major one and the engine dies.
Out on the idle adjustment screw raises the idle by allowing more air in.
Do you have A/C?

Mrmerlin

check for a shorted ignition wire or possibly a fuel injector plug could be loose

anonymousagain

Appreciate the feedback guys...

Mike, no A/C functional. Just a very low barely running idle now??

Mrmerlin, my understanding is that if an injector plug was loose, all injectors would cease to fire. As for ignition wires, no firefly's under the hood last night.

What if there was a crack in the Cap? Could idle drop out at low RPM be due to cross-discharge from the rotor?

Reaching for straws....

Bill Ball

Kirt: Not so. Only true if there is a short. If a plug falls off, that injector alone is affected.

anonymousagain

Ahhh, thank you for the correction Bill. I didn't see anythat look like they are backed away from the injector, but I'll work through each plug individually to ensure good seat just in case.

Strange that idle is completely unaffected by any idle screw adjustment...trying to adjust it either way only drops it further??

Outside question - since 16v, could it be possible for the TB to have skipped a tooth causing the "forced" idle at 400 because of timing??

SharkSkin

That's possible. is it slow and smooth or slow and lumpy?

See how a vac gauge behaves while idling -- smooth or erratic vacuum can tell you a bit about what's going on. Check cap, rotor, plug wires. Look for arcing in the dark or something that's disconnected.

It's probably not a vac leak, unless it's a big one as Mike mentioned.

anonymousagain

Dave - still feels relatively smooth as before, except at 400 idle since it's about to die. Doesn't feel any slower overall while underway either.

Hmmmmm....