Won't Idle When Cold

Blown88GT

Founding Member
Nov 13, 1999
2,242
549
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Palm Beach Gardens, FL
Have to feather the throttle for 5-10 minutes or it will stall.
For the next 20 minutes, idle will be high, around 1000-12000 rpm.
Once up to operating temp, idle holds steady at 700 rpm.
There are no bad codes.
ACT & ECT sensors are new.
IAB has been cleaned numerous times. It was removed & connected to battery with test leads; it functions when voltage is applied. You can blow through partially when no voltage & fully when 12V applied.
1. Could a partially blocked catalytic converter cause this? Whan it's cold, it doesn't flow fully; when it's hot flow is restored.
2. Or does it have something to do with open loop vs. closed loop? Won't idle right in open loop, will idle corectly in closed loop.
 
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The IAC is supposed to block airflow without any signal being applied to it. If you can blow through it, it isn't closing like it should. See my previous instructions on cleaning the IAC using a soak type carburetor cleaner like Gunk.
 
Ford idle valves sit naturally in the partial open position; engine vacuum pulls them closed, the solenoid then pulls them back open. The pintle moves freely on the bench.
It can't be any of this because it's fine when the engine is fully warmed up.
 
Have to feather the throttle for 5-10 minutes or it will stall.
For the next 20 minutes, idle will be high, around 1000-12000 rpm.
Once up to operating temp, idle holds steady at 700 rpm.
There are no bad codes.
ACT & ECT sensors are new.
IAB has been cleaned numerous times. It was removed & connected to battery with test leads; it functions when voltage is applied. You can blow through partially when no voltage & fully when 12V applied.
1. Could a partially blocked catalytic converter cause this? Whan it's cold, it doesn't flow fully; when it's hot flow is restored.
2. Or does it have something to do with open loop vs. closed loop? Won't idle right in open loop, will idle corectly in closed loop.
Hmm...I'm certainly not the expert here but I would like to help out if I can. From what I know (and I'm sure you know this also) an engine is in open loop until it reaches the operating temp for closed loop. It's not idling right in open loop. And it's not idling right while it's cold. Yet it is in OL while it is cold. Once it gets warmed up it idles fine. And in closed loop it idles fine. And again, it is in CL once it gets warm. So have you tried forcing closed loop at a colder operating temp with a tuner to see if the problem is with open loop or something else? Because if the problem is mechanical (EGR, IAC, etc) then forcing closed loop will not correct it which will rule that out. Then you'll know it's something else. I'm still learning tuning but maybe that will help you.

Outside of that I have to agree with jrichker...except that if it was the IAC then I would think the problem would exist even after the engine warms up. Since it doesn't (and there are no codes) then perhaps it's something else. Still tho my IAC went bad a few months ago. It was stuck open and causing the engine to idle high. I determined this by disconnecting it to see if the idle quality changed and there was no change. I replaced it and the engine ran fine. I'm not recommending you do that but you can always buy an IAC, install it, see if anything changes, and then return it if no change.

Another thing...I see your sig says you have a supercharger. Did this problem exist before or after the s/c? Superchargers put drag on an engine so maybe it needs more air. You might just need to open the throttle blade (and adjust the TPS for it) a bit more.
 
It's not the IAC Valve, tried JY one, same result. Supercharger has been there for 20 years, 30 lb injectors & MAF are new along with new A9L, Pro Billet & a host of other crap it didn't need. Degraded fuel pump sock clogged the pump, so new pump & sock. Installed Ford Idle Air Adjuster & it tried to stall once, idled OK then at 1500 until completely warm, then 700. It only took about a minute until I was able to drive away. Removed the connector to the IAC, idle was still 700 which makes sense given what the Idle Air Adjuster does. The IAC tried to open but isn't fast enough without the Idle Air Adjuster. With the Adjuster IAC seems to function better. Haven't tried to adjust the Bypass, if it keeps it from stalling & idles high for 5 minutes, I can live with that. I tested both IAC's on the bench, both function identically, full stroke with power applied. Normally they are pulsed by the computer for some position in between.
http://www.latemodelrestoration.com...Mustang-50L-58L-Idle-Air-Control-Iac-Adjuster

jrichker may know a lot, but he's the one that said it must be the PIP because there was nothing left, after running all his tests. There was nothing wrong with anything electrical, everything has been fuel related. I'm off the electrical bandwagon now & I'm the electrical engineer.

BTW, "tuning" is just a buzz word for those that don't understand. 20 years ago there were no tuners & no dynos. Electronics is not the answer to everything. All the new stuff is junk, anyway. Anything & everything made in China is crap. How do you think they make everything so cheaply? It's all nice if & when it works.

I'm thinking one or both of the cats is partially clogged. When they get hot, they flow better. Will need my muffler shop to test & confirm.
 
I'm thinking one or both of the cats is partially clogged. When they get hot, they flow better. Will need my muffler shop to test & confirm.

See and

for a video on how to check catalytic converters. Watch the last 1/2 of the second video for tools and techniques that will work on a 5.0 Mustang.
 
This thread pretty much describes my situation: http://www.stangnet.com/mustang-for...e-after-adding-some-mods.811642/#post-8171800

Got it out on the freeway, it will do 70-80 mph with the throttle barely cracked. Can't do extended WOT until FMU is installed. No bad codes.

Has too much surge at partial throttle. Reminds me of when it was a draw thru, about 20 years ago. Blow thru cured that. The only real difference is the injector size (30 vs 19) & the MAF (76mm vs 55mm).

Am resetting TPS as low as it will go, about .83V at the current throttle stop setting.

Didn't help. Spoke with my muffler guys, it can't be the cats.

I suspect the MAF calibration tube is correct for WOT but not for small part throttle openings. I've spoken with C&L a number of times & they are unable to "think outside the box" they have created. Will try some different calibration tubes & machine some custom ones in my friends machine shop.

In this case, no one seems to have done an effective job of duplicating Ford's (Hitachi) original MAF's characteristics across it's entire range. Probably easier to do it with a MegaSquirt which uses speed density calculations.