Erratic Idle

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Sep 18, 1999 | 07:33 AM

jra2212

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Joined: Sep 1999

Posts: 3

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Erratic Idle

I have a 1975 Ford F100 with a 360 cid engine. The engine has a very erratic idle. It will idle between 700 rpm and 1200rpm with the engine constantly changing speed. I also have a spark plug that will quite often foul out. I have checked for vacuum leaks and have found none. I have also tried adjusting the carb fuel mixture screws and idle adjust all to no avail. I've replaced the distributor cap and ignition wires and plugs and still nothing got any better. All of the cylinders have good compression and it seems to run fine when driving down the road. My question is this: What do I need to do to smooth out the idle, why would I have a spark plug fouling out quite frequently and are the two problems related? I think that I may need a new carb but I would like to get some other opinions before I take that route. Any comments or advice would be appreciated.

Sep 19, 1999 | 04:20 PM

TomC

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Joined: Jul 1999

Posts: 126

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Erratic Idle

Might check the PCV valve and hose. Also check the brake booster for a vacuum leak. If you have an EGR valve,check that carefully. Sometimes the body rusts out next to the carb. The problem you are having could well be a vacuum leak. Last but not least, you could have some badly worn valve guides and/or valve sealing problems.