Bad Traffic - High idle?

[JerrySab]

SUP RANGER FAM

SO LittleGold is back up and running, and really doing so much better! Thanks to the collective wisdom here, of course. Really so grateful for this community.

So here's a new old issue, that I'd love understanding on. My hunch is a wiring issue, but it's definitely made worse when I get stuck in bumper-to-bumper Los Angeles traffic. I'll notice RPM creeping higher, very slowly, but up to about 1100 rpm while sitting in traffic. And then temp gauge starts creeping up as well. When I finally get home I throw it in park and RPM shoots up to like, 2200. And remains there for .. a minute? 2 minutes?

SO this time, I popped hood and carefully jiggled wires. And it stopped. MAYBE it's correlated, but maybe not. Would a bad ground cause something like this? Doesn't happen until after it's put in park. I thought maybe it's burning off excess fuel from all the hellish stop and go, but y'all are way smarter than I, and I'd welcome any insights.

https://imgur.com/Un1pMwt

 

[franklin2]

I believe the computer does have a different strategy programmed in it when the engine is getting too hot. It may advance the timing which would naturally raise the idle speed, but it also may purposely raise the idle speed in hot traffic conditions. This turns the fan faster and the waterpump faster, helping to cool things down.

If you think this is happening prematurely, you might want to look at your radiator. Take the cap off when it's cool and see if you have a lot of white corrosion clogging things up inside it. Make sure the fins are clear of dirt in the A/C condensor as well as the radiator. You can take the grill out and use a garden hose for this.

 

[RonD]

If you can repeat it, then when you get home and idle is 2,000 in Park open the hood and unplug the IAC Valve's 2 wire connector
If idle drops instantly then computer was setting the high idle
If it doesn't drop then you have a vacuum leak

 

[JerrySab]

Thanks gents!

@franklin2 I was wondering about CPU initiating something like thIs, totally makes sense. Even though coolant temp looks ok, maybe air charge sensor or oil temp are reading high, which would trigger sustained higher RPM. Im super paranoid of an injector being stuck open, which was a previous problem, and leaking a ton of fuel into the oil.

@RonD great call. Im choosing not use the truck for commutes where I know I’ll be catching traffic, but I’m eager to yank IAC plug if it starts up again.

Thank you both!

 

[JerrySab]

@RonD SO I finally had the chance to yank the plug on IAC after driving in to work. Same issue, noticed 1100 rpm while in traffic; put truck in park, tach jumps to 2100 and holds there. I popped the hood and pulled the plug, RPM plummets to base idle. plugged IAC back in, truck went back to 950 (which is where it always idles when warm; I think dash display is 100rpm off).

SO does this mean the IAC is toast? Super annoying because it's relatively new AND motorcraft. I did pull it off and clean it recently, but it seems to be sticking WIDE open in these instances. I have a non mc/Hitachi crap replacement I can drop in, but could this be a wiring issue? or even ECM?

I'm guessing I just have a failed part. But would LOVE to be told otherwise because ALL OF THE NEW REPLACEMENT PARTS NEED TO BE REPLACED ALREADY.

 

[Cees Klumper]

Can't help on the specific cause(s) but just to say I drive around LA regularly including in warmer stop and go traffic and my '90 Bronco II with the 2.9 always idles at a steady 700 rpm 'no matter what'. Only when it's cold it's around 1,100 but that's normal, as is the temporary jump in rpm when putting it in neutral.
Have you set the idle properly, meaning have you made sure a previous owner did not mistake the bolt on the throttle body to be the idle set screw? There is a procedure for that (I believe is a sticky post here). My engine also never overheats, so that may have something to do with your issue.

 

[JerrySab]

super helpful, thanks @Cees Klumper . Although probably not what I was hoping to hear, but confirming there’s something fishy going on. Since you’re local, do you have a mechanic you could recommend? I’ve been slowly DIYing this, which has been a great learning experience, but I would also love for mine to run as you describe yours.

idle screw has been all over the place, but I’ve followed the sticky here to dial it in. and have aHaynes manual.

 

[Cees Klumper]

Sorry no mechanic, so far I've been able to do all troubleshooting and repairs and maintenance myself with the help of this forum and all the very helpful and knowledgeable people here. There was one neighbor in our marina that helped me once diagnose a faulty fuel pressure regulator, who used to be a Ford mechanic, but he moved away. Good luck, keep at it, sounds like something simple like a vacuum leak or something.

 

[JerrySab]

yeah I figured. Earlier on, i took truck to a number of shops. None of them want to touch it lol. The one that did kept charging me for fixes and parts that somehow never made their way into the truck. So. TRS it is.

I know there’s something still out of whack, either w vacuum and/or ignition. Either way, thanks man!