No More High Idle on Cold Start

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harrydunn

harrydunn

10 Year 15 Year
Joined
Oct 21, 2007
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305
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Location
Columbia, MO
Hey, gang--

Been researching for a week or so before I posted but have not found a solution yet. '93 LC, 210,000 miles, runs great for the last six years I've daily driven it. First "cold" morning we've had here in the Midwest was last week and I was surprised to have it die on me at initial startup in the morning. Cranked it again and it started right up. What it is doing now is starting up fine, going to its normal high idle for two seconds but instead of staying there, drops down to an almost dying RPM for a second and then shoots up to a nominal idle RPM of 650. Idle and runs very smooth. Plenty of power. No CEL.

What I've done thus far:

*Removed throttle body and IAC and cleaned up both-they were not gunked up really at all.
*Tested the IAC per the FSM. Resistance is fine and it is moving by grounding the electrodes.
*Replaced the intake tube as there was a small crack in one end - no difference.
*O2 sensors are about 4 years old - Toyota OEM.
*PCV valve checks good and replaced grommet.

I'm tempted to put a different IAC on it but I hate to just throw parts at problems and it SEEMED to test out just fine per the FSM.

Thoughts? Thanks!
 
On a cool morning and it is kept outside the idle should stay at a higher RPM than 650 for a period of time. Is the battery strong with clean connections? Fusible links old? How many times has this happened?
 
Happens every morning the last 10 days. Idle does not stay high upon any start now. Most notable during the first "cold" start in the mornings. Battery is 11 months old with good connections. Plugs, wires, about one year old. Not sure about the fusible links. They are at least six years old which is how long I've owned it.
 
<60 degrees outside mine starts then idles @~1,100 then slowly comes down to ~650 in ~30 seconds. I would think your issue would have to do w/the IAC. Start the truck, turn on AC, lights, radio. What happens?
 
Change the links they are cheap. My guess is that somehow the ECM may be loosing power and reseting. You might check the 15A EFI fuse in the engine compartment to make sure it has good/clean connections, pull it out for 30 seconds to manually reset the ECM.
 
Thanks for the replies. I'll check some things out today and report back.
 
Ordered up some new links from my local Mr. T. Will install tomorrow. RPM's kick up when I crank the A/C on like it should. Pulled the EFI fuse and it seems to be starting "differently" now. Cranks up fine and hits the high idle point, but instead of falling on it's face for a second, it drops down to 650 RPMS, the same RPM it would be sitting at when warm. Runs great as mentioned. I'm just looking to get my high idle back which is hilarious because most people on here are trying to get rid of their ridiculously high cold start idle! :-) Does this point to the IAC valve regardless of the fact that it tested out just fine?
 
Pulling the EFI fuse resets the computer, it takes the computer a while to relearn some settings. During this time the engine will behave a little differently, it certainly doesn't hurt anything but thats likely why its behaving differently.
 
Correct. Knew that but I figured it would run like poop considering resetting the ECU in the past, either by battery disconnect or pulling the EFI fuse, has always resulted in a very low, rough idle until things get back to normal. Was very surprised when that didn't happen this time.
 
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I would try a new coolant temp sensor before a new IAC. When my coolant temp sensor was on the fritz the ECU thought the engine was cold all the time. Would idle at 2000 RPM at all times, even if you had been driving the truck for quite a while.

Now in my case that meant the truck (a 93) was running really rich, and pretty s***ty. I would imagine a truck with a failing coolant temp sensor that is sending a "warm" signal would drive pretty good.

My .02.
 
thatcabledude said:
I would try a new coolant temp sensor before a new IAC. When my coolant temp sensor was on the fritz the ECU thought the engine was cold all the time. Would idle at 2000 RPM at all times, even if you had been driving the truck for quite a while.

Now in my case that meant the truck (a 93) was running really rich, and pretty s***ty. I would imagine a truck with a failing coolant temp sensor that is sending a "warm" signal would drive pretty good.

My .02.
Click to expand...

Would your temp gauge always read low when this happened?
 
Looking at my FSM (94) there is a temp switch and a temp sender. I got a sudden high idle after changing my oil 6 months ago and it looks like both the switch and the sender are in the vicinity of the oil filter, I'm thinking I might have bumped while changing the filter.
 
I like the ECT sensor idea but I believe you get a CEL if you're sensor is jacked up. Yes, no?
 
When my issue was occurring I had the light pop on VERY briefly for rich condition a couple times, but for the most part there was no light. It did not come on for the temp sensor itself.
 
Okay, thanks. I'll try to find the part # and swap 'er out.
 
New fusible links installed. We'll see how it does. QUESTION: If it were the coolant temp sensor that's causing it, wouldn't it be misbehaving much more than stumbling at cold startup and then not kicking in high idle when cold? Truck runs ridiculously smooth at all RPMs and at idle. Power is great. Just no high idle.
 
Tested the engine coolant temp sensor today in hot and cold water. It tested fine with my multimeter. I can't in good conscience replace that for what they cost if it appears to check out. Any other thoughts?
 
harrydunn said:
New fusible links installed. We'll see how it does. QUESTION: If it were the coolant temp sensor that's causing it, wouldn't it be misbehaving much more than stumbling at cold startup and then not kicking in high idle when cold? Truck runs ridiculously smooth at all RPMs and at idle. Power is great. Just no high idle.
Click to expand...

You said "power is great" so obviously you don't have the 1FZ-FE Under the hood ;) sorry, had to...

My 93 had done this a few times, but not recently, and cured itself, never had it happen with my 95...

I would think maybe it's something to do with the signal to the IAC valve, although you said the idle bumps up when a/c is on, it just seems weird that the temp sensor and IAC valve test good and the problem persists...

I am one of those people who hate the high idle, wakes my son up most mornings :(
 
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