Greetings people wiser than me,

I have a 2000 F150 4.6 with about 130,000 miles. When I come to a stoplight the engine RPM's drop very low and then bounce back up, it has even died. The problem is worse when the air is on due to the extra drag on the engine. I have read other posts on this problem and still haven't figured it out. I did at one point have an EGR code - so I tested the EGR valve by putting a vacuum line on it and gently applying suction and the truck started running very poorly, almost died. So I ruled out the EGR valve and blocked ports and changed the DPFE sensor (I believe thats what it was called, can't remember) and never had the light come back on. I have also changed the Air Idle Valve with no change. I then assumed I have some sort of vacuum leak. Visually, all the line appear to be ok but I also sprayed around the engine and vacuum lines while it's idling with carb cleaner listening for any idle change - still nothing. I am baffled, so I am turning to my fellow f-150 friends.

Thank you in advance,
Jack

 

You need an IAC valve. Get one at the dealership (recommended)

Your going to all new vacuum lines, EGR valve (since the diaphragm will probably go out soon) . Anywhere you sprayed carb cleaner on plastic or rubber lines will need replacement now, - or very soon. Never do that, it will tear them up.

 

I did replace the IAC valve. I also know carb cleaner is harsh, but it evaporates quickly. I then treated the hoses with armor all tire foam and wiped them clean. Also as far as the EGR valve, it worked perfectly and didn't lose vacuum. It may go out someday, but it clearly is working.

 

Replace the IAC again, with a dealership part. Yea, carb cleaner will evaporate when exposed to air, but will not at the connections where it is trapped between the rubber and plastic. It eats materials away creating adverse effects upon the system.

Don't waste time debating me, listen and learn.

 

Low idle causes =

#1. IAC valve.
#2. EGR valve. Valve could be hanging (your diagnostics does nothing for this problem).
#3. EVR Malfunction.

Hard to say once you hose it down with chemicals that compromise components.

 

JBREW, I do appreciate your input an will never check for a vacuum leak with carb cleaner again. You also mentioned my EGR diagnostics didn't matter. After changing the DPFE sensor, my check engine light reset itself. Is there something else I should test on the EGR system or a different way to test it? Also I don't believe the new AIC is faulty, because the old one I pulled out showed signs of working properly (the actuator rod inside was shiny from movement). So it didn't I wasn't shocked when the new didn't solve the problem.

 

Also, I May be nuts, but it seems to only happen after the trucked has reached normal operating temperature, which lead me to believe it was EGR related.

 

EVR= When it's idling low and about to stall, -pull the green line. If idle returns to normal, you have a EVR problem. @ Idle there should be NO VAC (0 hg) at the green line.

Normal idle is between 700-750 rpms , or you have a problem. 730 rpms is average.
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EGR= You'll have to pull valve to check that it's closed. Or tap it while the engine idle is below 700 rpms in order to determine if it's hanging. Sometimes that works, sometimes it don't.

 

Hey JBREW.. crazy question, since it dips and returns so quickly, I wouldn't have time to pull a line or even if I did I wouldn't know it was because I pulled the line or the computer caught it. Would disconnecting the EGR valve and plugging the vacuum line give me any clue?

 

Yes - pull the line and plug it. You will probably throw a P0401 but don't worry about it. If the idle fixes itself, the EVR needs to be replaced or the EGR valve itself is sticking.

 

I am having this problem too with my 97 5.4. but when it drops down and loops hard it wont go back up. it continues to loop and it will do it when ever I idle (stop lights, stops signs, park, drive any gears) I have to hold the brake and ease on the gas to keep it at like 1k till I can take off. any suggestions? I'm not good with motors so I need help.

 

I pulled the line off the EGR valve and plugged it. I did get a code fairly quickly, but the problem did not go away. Any ideas?

 

Change your fuel filter, - then check pump and regulator pressure. Rule out a fuel system problem first.

 

I think it may be worth pulling the throttle body and cleaning it - and pay particular attention to the EGR passages, they are known to clog on 4.6's. It also may be wise to pull the EGR valve and clean it too, there may be some crap in there that's preventing complete closure. Check the vacuum lines in the EGR system - from the DPFE, etc.

 

Hello, and thanks for the help. I don't see any obvious signs of a vacuum leak (visual inspection & listening) I do believe the egr valve is closing do to a test I did with applying vacuum to it and releasing it. JBrew mentioned it could be sticking, but I have unplugged the vacuum line from the egr valve and plugged the line. I got a code fairly quickly, which I expected, but the problem continued. I have replaced the idle air control valve, although the one I pulled off seemed to be working judging by the actuator rod inside was shiny from what appeared to be full movement (I know it still could have been malfunctioning) it just seemed weird the new part didn't help either. The problem only seems to happen when the engine is at operating temp. Any ideas would be greatly appreciated.