302 w/idle problems
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New User
Joined: Jul 2010
Posts: 8
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From: Cartersville, Ga.
302 w/idle problems
I have a 91 F150 with a 302 that I just purchased. It is a 5 speed. The check engine light was on. Checked code and found TP sensor problem and fixed it. Someone had advanced the timing to 20 degres. Set timing to 11 degres and had to replace Idle Air Control Valve. It was running very well, no codes but now the idle is jumping all around. Twice it has jumped to 3000 RPMs while waiting for train or light to change. The idle is hanging at 2500 when changing gears and it surges up and down. Any ideas please help.
More Turbo
Joined: Mar 2010
Posts: 539
Likes: 25
From: Atlanta
Subscribing. I have a 92 f150 302 m5 with 190k miles. I have had the same problem off and on for the last 100k miles. I have changed the tps, iac valve, throttle body, checked for vaccum leaks, lubed throttle cable. It never throws any codes. I ran out of ideas a long time ago. Right now it seems to be ok but it will come back it always does.
New User
Joined: Aug 2010
Posts: 11
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I have a 1990 F250 / 302 and its been doing the same thing. CEL has been on for a while. I have changed the IAC and checked cables. I'm sure its not something sticking now because when it goes to 2500ish RPM at idle, if you quickly turn the key to OFF then immediately back ON (so fast that engine's own rotation starts it back up) the idle comes back to normal. But NOW, the idle is constantly messing up to the low side also. It will go down to 400 RPM as well. Then it started bogging down as soon as you put a load on the engine, even at 700 ish RPM, unless you get it to approx 1500 RPM first. Then it will drive normally except the occasional roars to 2500RPM's when you shift gears. However, it started just quitting once it gets hot and you have shut the engine down. In fact, I just took the bus home. Drove it and it ran OK. 20 minutes after shutting it down, nothing at all. Have pulled a spark plug and showing no spark. This is the second time this has happened this way. I changed the coil, the ignition control module. Nothing. Mine seems to be heat related. No idea what to check next, and neither does the nearby professional mechanic.
Hotshot
Joined: Sep 2001
Posts: 11,958
Likes: 228
If it has an erratic or surging idle then I would think it could have a vacuum leak. Its something to check and could be a cheap fix.
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Fleet Owner
Joined: Oct 2005
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From: Kentucky
I have a 1990 F250 / 302 and its been doing the same thing. CEL has been on for a while. I have changed the IAC and checked cables. I'm sure its not something sticking now because when it goes to 2500ish RPM at idle, if you quickly turn the key to OFF then immediately back ON (so fast that engine's own rotation starts it back up) the idle comes back to normal. But NOW, the idle is constantly messing up to the low side also. It will go down to 400 RPM as well. Then it started bogging down as soon as you put a load on the engine, even at 700 ish RPM, unless you get it to approx 1500 RPM first. Then it will drive normally except the occasional roars to 2500RPM's when you shift gears. However, it started just quitting once it gets hot and you have shut the engine down. In fact, I just took the bus home. Drove it and it ran OK. 20 minutes after shutting it down, nothing at all. Have pulled a spark plug and showing no spark. This is the second time this has happened this way. I changed the coil, the ignition control module. Nothing. Mine seems to be heat related. No idea what to check next, and neither does the nearby professional mechanic.
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Junior User
Joined: Apr 2005
Posts: 51
Likes: 0
From: North Carolina
Possibly the EGR valve on the passenger front side... $106 for a new one at Auto Zone though. I am having a similar problem and changed the IAC valve and cleaned the throttle body, etc. It went away for 2 weeks or so and now started back up but a little different. EGR valves will eventually get dirty and build up with carbon I believe so I would pull yours off and take a look at it.
Junior User
Joined: Apr 2005
Posts: 51
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From: North Carolina
I didn't say it was causing a no spark condition. I read his first couple of posts and put my answer down. If he later said something about him narrowing it down to losing spark then that is a different story.
Junior User
Joined: Apr 2005
Posts: 51
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From: North Carolina
LOL no problem. You caught the question I missed and visa versa. It happens. I re-read my post and I sounded like an *** but didn't mean it like that just to let you know. If he is losing spark, how about the ignition module on the drivers side firewall or fender towards the firewall? I am not sure that is the correct name for it but it's the silver box with the louvers in it. I hear these are problematic on some of these Fords because they are not mounted in the front near the radiator like the newer models are, therefor they heat up and eventually go out (that's electronics for you). 
