Idle Problem when Cold

ab_slack · Nov 5, 2016

This is somewhat an intermittent issue and I can't say it happens every time at cold.

We have had a problem where our 99 Ranger with a 3.0L would not idle. It would stay running as long as one depressed the gas pedal while starting. Once you take your foot off the gas it stalls. If you don't put your foot on the gas while crank it will catch but then immediately stall.

There is never any CEL and no codes are stored.

After it warms up it seems fine. Any suggestions as to likely causes? Not too familiar with this engine.

Most irritatingly is that I can't guarantee it will happen to diagnose it. Though it always happens when the car is needed and I am away.

I was thinking maybe the ECT is sending wrong info so when it is cold out and engine cold it isn't providing a rich enough mix.

Or maybe the IAC valve getting a bit sticky at the end of its movement where it needs to sit when it is cold out.

I am guessing someone who knows this engine betters knows what a likely culprit will be.

Thanks

RonD · Nov 5, 2016

Yes, the ECT sensor or IAC Valve are good guesses.

You can get a Bluetooth OBD2 wireless reader for under $50
You use a smart phone or tablet with Bluetooth and app to connect with these to see the Live data or the codes.
And they work on any vehicle sold in the US or Canada since 1995, not a Ford thing, OBD2 is industry standard for any brand/model sold in US/Canada, so good long term investment.

Point being, you can look at Live data and see what temp the ECT sensor is sending to computer in real time, anytime, and also what computer is setting the IAC valve at.
Now ECT sensor is cheap to replace, and could be the problem, but long term the Bluetooth reader might be a better place to spend the cash.

IAC valve is free to clean

When you turn on the key the computer starts up and runs a self-test
Computer opens IAC valve all the way for starting, regardless of temp, this is why engine should REV up slightly when starting, anytime
It then looks at ECT temp to see if this is a cold start or warm restart.
If under 140degF computer sets Choke mode
It then looks at air/fuel ratio table for actual ECT temp and sets/calculates that ratio
And there is an RPM idle speed table based on ECT temp, after engine starts computer closes IAC valve to set this RPM.
The colder the temp the richer the mix and the higher the idle

To test IAC valve you can remove it and plug in its wires, turn key on and Valve should open all the way, turn key off and it should close all the way, repeat a few times to make sure valve isn't sticking.

Just as an FYI, the reason cold engines need a Rich Mix is that liquid gasoline doesn't ignite by spark, only gas fumes ignite.
The colder the gasoline the less fumes there are.
So to get a cold engine to start you need to add more gasoline to get enough fumes for ignition by spark plug

ab_slack · Nov 5, 2016

Thanks RonD, you know my guesses come from the education you, adsm08 and others on here gave me with my BII a couple years ago. And that BII has been pretty problem free lately except for the NJ rust. Damn the rust catching up on her quick.

Yep I was thinking about cleaning the IAC valve.

I tend to dislike anything Bluetooth just because everything I ever had ended up having poor reliably staying connected. Now I am trying to think if my plug-in OBD2 reader gives me live data. I am thinking not.

Thanks again

Idle Problem when Cold

ab_slack

Member

RonD

Official TRS AI

ab_slack

Member

Sponsored Ad

Sponsored Ad

Staff online

Members online

Member & Vendor Upgrades

Latest posts

Truck of The Month

Recently Featured

Follow TRS On Instagram

Latest Album Photos

TRS Events

25th Anniversary Sponsors

Check Out The TRS Store

Sponsored Ad

Sponsored Ad

Sponsored Ad

Amazon Deals