Rough Idle after 87 Octane
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Northstar Engines and System Technical Discussion Discussion, Rough Idle after 87 Octane in Cadillac Engine Technical Discussion; Saw a few posts re bad gas problems etc but thought I'd start a new one and list my concerns. ...
  1. #1
    Mitch3 is offline Cadillac Owners Fanatic
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    Rough Idle after 87 Octane

    Saw a few posts re bad gas problems etc but thought I'd start a new one and list my concerns. My 94 Eldorado started running sluggish and rough idle after using three tanks of 87 Octane HESS gasoline. I changed back to Premium HESS and it's a little better but still idles a little fast and rough when stopped and in gear (at red light etc). I know a lot of you claim 87 Octane is fine but it didn't work for me. I figured maybe a tuneup would solve the problem so had the plugs, plug wires, fuel filter, air filter, and pcv valve replaced which cost me $560.00. Wow !! That was a shocker.. After all that the car doesn't seem to run any better. Last night I was coming to a stop on an upgrade and thought I was stalling out but it came right back. Any suggestions ? At your suggestions I am going to try some dry-gas and Shell V gas. Maybe that will help.

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    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: Rough Idle after 87 Octane

    Damn! You got hosed on that tuneup! Everything but the fuel filter would've been easy to do yourself. Cost: $30 plugs, $50 wires, $10 air filter, $5 PCV = $95. Fuel filter would've cost you $10 more, but is a little more "safety involved". Anywho, don't know what to tell you... It's possible one of your fuel injectors may have taken a dump, and so it sounds like it's missing constantly, and running on 7 cylinders. How's your gas mileage? Did it go down? Up?

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    Leloz is offline Cadillac Owners Enthusiast
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    Re: Rough Idle after 87 Octane

    My guess is the EGR valve. Sometimes you can have the EGR valve cleaned, but it is a rather easy part to replace.
    HTH! goodluck

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    Mitch3 is offline Cadillac Owners Fanatic
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    Re: Rough Idle after 87 Octane

    Yeah........Thought I got hosed on that tuneup. Everyone tells me this guy is as honest as they come and he's done work for me before with no problems. Charged me $13.38 ea for plugs and $172.95 for the plug wires. Oh well, next time I'll get an estimate first. Mileage has always been good on this car and still is-----23 around town and about 28 on a highway trip. I bought this car from a garage that got it at auction, so there were no maintenance records with it to tell me if the plugs, wires, coolant etc had ever been changed. Ran a Vin number check before I bought it and it came back clean. Have had it for exactly one year and other than my $500 tuneup have spent no money on it other than oil changes. It's my first Caddy and I really love it. By the way it's got 117,500 miles on it.

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    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: Rough Idle after 87 Octane

    Could be a stuck open EGR valve as mentioned above... Could also be a cracked vacuum hose. Could also be some heavy-duty carbon buildup. There's lots of threads about how to fix that Might also want to give the "steam cleaning" procedure a try, or run some sea foam through it.

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    Re: Rough Idle after 87 Octane

    Your problem may have come from getting some gas with water in it or something along those lines but it had NOTHING to do with the 87 octane fuel. It might have been the fuel that you bought that caused the problem but not because it was 87 octane....the same problem could have occurred with any fuel.

    The octane rating of the fuel has nothing to do with the idle quality or any rough running or anything. It is strictly a measure of the fuel's ability to resist spontaneous combustion that causes detonation or spark knock. The octane rating has nothing to do with burn rate, burn temperature, carbon formation, deposits, cleanliness of the fuel or anything else along those lines.

    No doubt you might have gotten some "bad gas"....but it wasn't the octane rating of the fuel that caused the problem.

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    Re: Rough Idle after 87 Octane

    I had the same problem just about. It took about two half tank fillups and at last, a full tank fill up before I got rid of it. Also put in a bottle of water remover. By coincidence, I was using Hess gas also, but here in Florida. I have been using Hess gas for some time and never had a problem with it. I heard compliments of the Shell V-Power. A new station had just opened up recently. Their prices are the lowest and needless to say, I am now their loyal customer. And the Eldo, running smooth again.

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    Mitch3 is offline Cadillac Owners Fanatic
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    Re: Rough Idle after 87 Octane

    Well, I'll never know for sure what cured it but I tried a few things you all suggested and the old girl is running like a charm. First, I took her out on the thruway and blew the hell out of it. Put in a bottle of drygas and filled the tank with 93 Octane Sunoco. Gave her a good run on the thruway for about 25 miles. Problems seem to be gone. Now if I could just put that $500 tuneup out of my mind!!!!!!!!!!!!!! Thanks, everyone, for your advice.

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