fast idle??
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5.0 and 5.7 Discussion, fast idle?? in Cadillac Engine Technical Discussion; my caddy always seems to run at a faster rpm then it should. i have owned it 2 years and ...
  1. #1
    89fatb's Avatar
    89fatb is offline Cadillac Owners Fanatic
    Automobile(s): 1989 fleetwood brougham 145k
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    fast idle??

    my caddy always seems to run at a faster rpm then it should. i have owned it 2 years and every time when its cold i would pump it once and fire it up then pump it once more to kick the throttle back down now recently i will do that same thing but as soon as i start driving,or put my foot on the gas it returns to a faster idle. it never did that before? i thought it was my choke staying on, so i backed it off a little to no avail. i drive 20 mins to work on the freeway, 70mph and when i get to work it still is to high. i can kick it down. is there an fast idle adjustment? please help

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  3. #2
    caddydream is offline Cadillac Owners Member
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    Re: fast idle??

    When it is warmed up sometime take the aircleaner top off and check to see if the choke is fully open. If it is open you might have a problem with the Idle Load Compensator (ILC). A lack of vacuum to it will cause the idle to be high. The ILC is located next to your carb on the same side as the throttle cable. It has a plunger and will push the throttle at a higher RPM when the AC is on.

  4. #3
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
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    Re: fast idle??

    Check the primary vacuum break, I have rarely found a good one in a junkyard.

    You should be able to TAP the gas pedal to take the tension off the choke so it can close and the car should start VERY easily. You should never need to fully depress the gas pedal to start it. Wastes gas bigtime.

    Caddydream is correct, the ILC (look for my post on here describing its operation) can easy develop a leaky vacuum line causing idle to creep up higher and higher as it leaks.

    There is 2 ways for vacuum to enter the ILC, either is ok to use, the other SHOULD be plugged, make sure plug is ok. Ensure the ILC will hold vacuum and is not leaking.

    Your choke should be 100% fully open in 3.5 minutes of any cold start on an Olds 307.

    DO NOT ADJUST THE ILC!! It is not meant to be messed with, adjustments are a pain, so please don't mess with it, you are better off removing it than messing with it. But that can lead to engine stall on hard decel.

  5. #4
    akimball442's Avatar
    akimball442 is offline Cadillac Owners Fanatic
    Automobile(s): '81 CDV, '84 Olds 98 Coupe, '81 MB 300D,'73 450SL, '88 300SE
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    Re: fast idle??

    I'd almost bet my life its the ILC. ILCs in 307s love to leak and boost the idle. The other side of the coin is you HAVE to find one in a junk yard, becuase its not availble in the aftermarket or from GM dealerships anymore. And good luck with that. You'd think that a frequently failing part on a very common engine would still be availble, they'd probably sell them like hot cakes. What I did was grab an electronic solenoid off of a late 70s olds with a 350. It bolts right on in place of where the ILC goes, and even the throttle return spring attaches in the same place. There are two ways to hook it up, and if someone needs more info you can email me. Number one is simple, just run a wire to the side of the A/C compressor that has B+ voltage when the A/C is on. This will keep your idle about right with the A/C running. Somebody above mentioned that the ILC is designed to also help prevent deceleration stalling. That is true, also, the plunger fully extends when you shut off the engine to prevent dieseling... which is something else 307s are notorious for. The best solution is still to use the electronic solenoid, however, on 307s the ILC, even though it appears to be vacuum actuated, is actually electronic. The vacuum line goes to that box on the rear right hand side of the engine. That box has 3 vacuum switches in it which control EGR, the ILC, and something else, my mind draws blank. Anyhow, you can take the wire from that box that controls the ILC switch and get clever with a relay so that the new solenoid is energized when the ECM thinks it should be, just likt the ILC was. I hope that wasnt too wordy, but being a hardcore oldsmobile fan, I have, and have had many B-body delta 88s and C body 98s which are great cars, and have all had the ILC fail. The 307 gets a bad rap. Its an excellent motor, and it can be made to perform just fine. A Fleetwood Brougham isnt a muscle car. A properly tuned 307 can give you enough power to spin the rear tires at a stop sign, safely pass the old fart going 45 on a country road, and return 22+ average miles per gallon all day long for 200,000 miles if you keep it properly maintained and drive it reasonably. I have an 84 olds 98 right now with 265000 on it which runs acceptably well. I put on a regular distributor and a holley and it can peel out for a block. I am replacing it with an olds 350 that I built, then it'll really move. Of course, thats a bit lighter of a car than a cadillac. Just a thought. If anyone wants to get in touch with me about simple performance mods to the 307 (most of which are things that actually just restore it to its original condition) feel free to email me. I'd love to see more people get enjoyment out of these bulletproof motors. my email is akimball442 @ hotmail . com (spaced to prevent spam). Of probably 12 I've owned, i've only had one 'blow up.' The oil pump failed.

  6. #5
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
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    Re: fast idle??

    FWIW, the electric idle solenoid that akimball talks about is std issue on the "9" 307. I don't know why they felt the "y" engine couldn't handle it, but they did....

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