Cold Idle Control issues.

[907DAVE]

Now that the winter is here my cold idle control is in the dumps.

This is an issue that presented itself a few years ago when my alternator was not charging well at idle, or whenever there is an accessory left on that drops battery voltage.

Problem is that whenever there is a decent draw (or low voltage) on the charging system the "automatic high idle" will not work. If I leave all accessories off (heater, lights, radio) it will work normally.

Tonight I payed around with it a bit........I went in and setup the Cold Idle Multiplier and Cold Idle Control to always be in "high idle". This worked great until I flipped on the lights or heater, then right back down to normal idle speed.

The system voltage (according to the Scangauge) is right at 14.2-14.4v.

I am starting to get a bit irritated with this as the truck really does not warm up to well at base idle, and I am not willing to turn off the heater.....lol.


Any ideas why this is, or what parameter to adjust to relax this a bit?

[cleatus12r]

Hmmm. No problems here. Last night after reading this post I went outside and started the truck. It was 20 degrees and I instantly turned on my HVAC blower to high, turned on my lights, and waited.

20 seconds later (glow plugs still on as well as all loads), the truck was in it's high idle mode.

[907DAVE]

Ya, I know it is strange. Guess I could always just put the chip back in, or that box, but I would rather find the issue then cover it up.

I might hook up the BOB and see what voltage actually is at the PCM during this condition.

[Colt]

So what your saying is any time there is any kind of current draw, the truck wont go into high idle? You alt at one time didnt charge well, but now it looks to be charging ok?

I've had issues in the past with the race car, when the alt would start to give out, it would tend to scramble the firmware in the EFI computer. I always knew when I was getting ready to lose an alternator because I'd get a bunch of noise on the sensors..

The only conditions that I know of that have to be met for your truck to go into high idle is, has to be in park, the throttle pos. sensor has to be within a certain range, the brake light switch, and engine oil temp cant be above a certain temp. So I'd look at what the sensors are doing, see if your getting and kind of noise that might not allow it to go into high idle..

Whats the engine oil temp when it's doing all of this?

Thats really all I can think of.. It's been in the low teens here in the mornings, and my truck has gone into high idle everytime without an issue. Thats with the heater going full bore, stereo system going, and typically with the lights on.

[907DAVE]

Originally Posted by Colt

So what your saying is any time there is any kind of current draw, the truck wont go into high idle? You alt at one time didnt charge well, but now it looks to be charging ok?

Yeah, seems to be working fine, no noise (AC volts) in the charging system either.

Since posting this I had gone through all my battery/ alt connections and cleaned everything, regardless of how it looked.

Since then it has seemed to be working normally.

There must be an undefined table that has some bearing on this...............ohhh Bill!!!!

[907DAVE]

Well I thought I had the issue resolved until temps dropped to -40 for the past week or so - and it stopped working again.

Using the Scangauge I monitored the IAT and it was reading 500* (which I now believe is an issue with the Scangauge), so I disconnected the sensor and it defaulted to 68 and the high idle seemed to work normally - when the engine was cold.

Today I spent a bit of time playing with it and was pretty successful controlling the idle with the sensor disconnected, once it warmed up I lost all control of the high idle.

I tried changing the default to 0*F , setting the Cold Idle control to be always on - regardless of temp - and it still wont work when the engine is warm.

When the sensor is disconnected does it substitute a different temp sensor?

As a last ditch effort I plugged the sensor back in, and still no high idle function.

[Power Hungry]

Originally Posted by 907dave

Yeah, seems to be working fine, no noise (AC volts) in the charging system either.

Since posting this I had gone through all my battery/ alt connections and cleaned everything, regardless of how it looked.

Since then it has seemed to be working normally.

There must be an undefined table that has some bearing on this...............ohhh Bill!!!!

I'm looking into this. There's only one problem. I'm having a little trouble generating the -40º temps out here.

The issue definitely seems related to your IAT as this has significant bearing on the Cold Idle control. Case in point... I was in a truck on a roughly 15º day and the engine was sufficiently warm because I was inside tuning it. After a short bit, the idle ramped up even though EOT was well over 100º. This indicates that the idle strategy does look at IAT as well as EOT to control high idle.

Now the big question is, where does this function go awry? Is the PCM actually miscalculating the IAT output or is the scan-tool miscalculating the PID data and handling it as an unsigned value instead of a signed value? These are question I don't yet have an answer to since my truck is in GA and I'm in FL, but I will certainly be happy to investigate this and see what's up.

Stick around...