1985 Ford Mustang Engine won't idle unless the the adjustme

TMASTRACCHIO

MEMBER
1985 FORD MUSTANG
V8
2WD
MANUAL
135,000 MILES

Just a little history. The car has always been a great runner, 24mpg on the highway. The motor has about 45,000 miles since it was freshened up. I was driving at about 45 mph and lifted off the throttle quickly, after that it stalled and wouldn't idle. I had to turn the throttle adjustment screw all the way in so I could drive home without stalling. It drove fine and didn't seem to have lost any power but I know there is something that isn't right. I have replaced all the vacuum hoses I could see and checked the vacuum guage after each hose replacement. Not much improvement, so I plugged all the hoses and fittings from the intake and carb. The guage reads 15" @1000 rpm with all the vacuum lines plugged. Is that a normal reading for a 5.0 liter? I haven't removed the carb yet, maybe a piece of gasket broke off and that is where the leak is, I'll check that tomorrow. I can't really hear any vacuum leaks, last time I checked the timing I set it to 10 degrees BTDC. Let me know what you think about this, I'm a little stumped.

Thanks,
Tom

7 Replies

RACEFAN966

MECHANIC
5,029 POSTS

Ok what carb is on it? I know it will be a motorcraft but there are a couple of different ones. If you like take a pic of it and include it in your response. Also have you checked the plugs cap and rotor and have you used a spray bottle to check the intake for vacuum leaks? Get back to me and we will go from there.

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Monday, February 23rd, 2009 AT 2:48 PM

TMASTRACCHIO

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I checked the cap and rotor, no cracks. I sprayed the base of the intake with windex and didn't hear a change in the idle. I checked the plug wires with a neon spark tester and all eight plugs are firing. I attached some photos of the carb.

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Tuesday, February 24th, 2009 AT 9:38 AM

RACEFAN966

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Ok so you have a holley 4bb carb. No problem. So first check for any vacuum leaks around the base of the carb. Check the brake booster for any vacuum leaks too.
Now there is on black smoke coming out of the tail pipe is there? Have you slightly snuffed the carb with you hand to make it rich and see if it helps or spray short bursts of carb cleaner in it while it running to see if that helps it want to idle better? Get back to me with all the info you can so we can figure this out

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Tuesday, February 24th, 2009 AT 10:37 AM

TMASTRACCHIO

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Currently I have all the vacuum lines from the manifold and carb blocked off. If I read 15" of vacuum is that too low?

Thanks,
Tom

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Tuesday, February 24th, 2009 AT 10:33 PM

RACEFAN966

MECHANIC
5,029 POSTS

No that is good the higher the elevation you are at he lower the reading will be too. So did you slightly snuff the carb with your hand and see if that helped?
Also you can probably hook all the vacuum lines back up. If you need to adjust it then they will all need to be hooked up to adjust it right. Get back to me as to weather snuffing the carb or short bursts of carb cleaner sprayed in carb helpes it idle or idle higher.