I have a similar problem to a previous post. 2001 screw 4.6 w/ 190,000 mi. About half the time i start the truck up (hot or cold) it fires right up, goes up to about 1600 rpm and then when every other motor would idle down - mine dies. It will do this succesively (even a word??) 2 or 3 times. A little help with my foot will keep it running. Once it is running, idle is usually about 500-600 rpm. Seems and feels a bit low. On top of that stuff, the truck surges through the whole rpm range, idle to redline. What I mean by this is it hesitates every few seconds with steady throttle down. When I've got my foot in it it feels like the power output is alternating between 50% and 100%.
I'm starting with the plugs (its been a long while). Any help would be greatly appreciated!!

G4

 

I'd say maybe IAC (idle air control) or the TPS (throttle positioning sensor) to start, IAC would be the place I'd start. The coils may also be another place to start, as well as plugs. It might not be a bad idea to replace all these things especially if they haven't been yet. A good idle in gear is 600 steady and 750ish in park. How about things like fuel injectors and filter? Has the filter been changed lately? You're right, it's weird but could be one thing or a combination of things. Tuning up items might be good regardless to isolate the problem. I'll bet it's the IAC still, try cleaning it out and see if it changes anything because to replace it is 75 bucks and up usually.

 

Make sure to use the correct Motorcraft plugs and also get new COPS. Also would recommend changing the fuel filter.

 

Thanks for the replies guys. From what i read before i posted I went ahead and cleaned the IAC as best I could. It seemed to improve startup and idle, but now the IAC howles like crazy , only at or slightly above idle. Idle seems to be at a solid 700. I did change the fuel filter recently. I think you might be right about a combination of things. The truck still surges all throughout. I have the motorcraft plugs, so im gonna start to swap those out now. How much damage would the coils do to my income??

 

96 bucks plus shipping for all 8 from Global.

 

Not as bad as I would have thought. I've got the IAC back off to try and make it stop howling. Any suggestions??

 

Replace the IAC, if it's howling and I know what you mean, had one on a 99 Explorer 4.0, but running it a bit as well as disconnecting then re-connecting while running seemed to help, don't know why. Count on a replacement, but ebay has coils like mentioned for like 96 bucks (set of 8) or at most under 200 bucks and all are Motorcraft. New coils and plugs ought to solve or greatly improve the situation.

 

Yea , replace, that's when you know its time - When they start barking at the moon..

Rock Auto is about the cheapest as far as IAC's if you purchase from there ebay store -

http://cgi.ebay.com/ebaymotors/ws/eB...139885421&rd=1

 

Thanks guys for your input. I have the new plugs, but i'm gonna wait till I get a set of COPs first. I ended up cleaning the iac again and filling it with wd40 to soak for a while. When I put it back on it howled less, but then this morning it was gone and the thing starts up and idles great now. I'll see how long it lasts till I replace it