I just got finished dropping a Cadillac 500 into my 74 Chev 4x4. I got this engine kind of by luck but the more i researched it the more i realized it was the perfect motor for my big 3/4 ton 4x4. Well i got it planted in there and it runs pretty good if i were wanting to drag race my truck. unfortunately i want to wheel off road and i need it to idle and go slow with torque. It currently has an surging, loopy idle, it either feels like its about to die or running at 1800 rpm. It also seems to have a miss and vibrates a lot at idle. Might be running on 7 cyl, I'll check the plugs and wires tonight. Currently it has a Holley 750, Holley Digital Ignition System and coil, Pretty sure I got all the vacuum leaks stopped, I have a built TH 350 behind it (just since the TH400 i got with the motor wont fit my t-case) .. This motor is has awesome power:want: and accelleration but i need a smooth low idle for rock crawling. Any Ideas?

Just checked vacuum..... running a steady 12 in at idle... drops to 0 at WOT, and increases to 15 when decellerating.... about a steady 15 at 2000 rpm.. is this normal for a 500 or did the previous owner put a cam in it? I'm thinking power valve in the holley carb is loading it up... Any thoughts?

The 500 is the perfect "Torque Monster" unless someone drops cam in it. How much do you know about the engine? What was it built for? You may have to put in a cam that works for your application. You will want to match a good intake manifold for it then too.

Also, depending on which model Holley 750 you have, you will want to tune it to match cam and intake. There are dozens of variations for most Holleys.

Triple check for a vacuum leak. There are a few spots where the Horriblley might not seal to replace a Rottenchester. Try spraying some carbonater cleaner around to see if the idle rises.

One other thought;
If you are rock crawling you might find yourself in an angle that causes havoc with the carb. You might want to look into a fuel injection system for it so you don't 'run out of gas' on a 45+ degree angle.

Another place for a vacuum leak would be some of the AC compressor bolt holes. Several go right into the intake ports.

Got it fixed! First put new plugs in, looks like in the last car they had it in they coldnt get the #8 cyl changed, Second had a cut in one of the plug wires so i put on an extra i had, third changed carb to an edelbrock 1406 650 cfm that i had rebuilt for my last motor to run the high altitude (i live at 7200 feet). The last really made the difference. Pretty sure the holley needs to be rebuilt since it was running waaaaaay rich no matter what i did. Still pulling only about 14 in of vacuum at idle which still seems a lil low but at least its idling steady at 500 rpm in gear. no hesitation or anything and IT SCORCHES the tires on my 5000 lb truck. I have all the other car guys at WyoTech jeolous of my cubes. I put a single 3 inch exhaust on there that runs real quiet (and considerably more affordable) and still have the 350 tags on my truck. excellent sleeper effect i believe. Since this is a long bed truck with stock suspension its not going to see to many extreme trails so i think the carb will work for the time being. At least til i get the 6 inch lift put on there. Thanks for your help!

Wouldnt the 500CI be a little harsh on the TH350?