Hey guys,

Here is the next problem. 1986E auto, coupe L98.Idle goes up and down from 800- 1600 at anytime, but likes to stay around 1300 the most.The car radomly makes a hissing noise coming from under the Intake Plenum, them surges, then sometimes dies. Wait a few mins then it starts right back up.

The Service engine soon light comes on and off randomly too. Im going to see what code it gives tonight. What do you guys think?
Thanks Ryan

 

The hissing noise is a vacuum leak which explains your idle problem. The ECM attempts to control idle based on a sealed intake and a vacuum leak is unmetered air, so it "hunts" for an idle to try and control idle. Fix your vacuum leak and you will probably fix you idle problems. (Hint), if you do, disconnect your battery for a couple of minutes, then reconnect it and go drive it to let it idle relearn.

 

Hint....Take out some black electrical tape and tape out the service engine light then go to ecklers and buy the console cover with the emblem on it! Did that but taped out ALL the lights. Yep. No more pesky lights. Improvise.[&:]

 

Groovy, Any tricks for finding the vacuum leak with out taking the plenum off? Im heading down to the garage in a few mins!!

 

You can use a piece of heater hose 2 or 3 feet long, put end to your ear and the other to listen around to isolate where the leak is.

 

There are a couple of other tricks to finding leaks also. One is to use WD-40 and spray it lightly around your vacuum lines, when it finds a leak usually your idle will increase slightly momentarily. Another is to use a small propane torch (unlit of course) and turn the propane on ON A VERY LOW SETTING and run it around your vacuum lines, it will burn the propane when it finds the leak and the idle will increase. You must be very careful when using this method and DO NOT USE TOO MUCH propane, it only takes a little.