92 Ex won't idle high (warm up) when cold...

[eclipse5302]

Hey guys

My 92 won't idle correctly when cold. Usually, when the truck is cold it should idle high (about 1200 rpm) until it warms up...like any vehicle does.

My truck will start up, and drop right down to like 800 rpm in the morning. I already replaced the ECM coolant sensor, thinking the ECM doesn't know the truck is cold. It helped a little, but not much.

I have yet to hook up a scan tool, but I was wondering if anyone had any ideas.

Jason

 

[dogfriend]

The infamous IAC valve is supposed to control this as well by opening up to let more air in (along with a longer injector pulse time to richen the mixture). Perhaps yours is sticking.

Its more of a 2nd gen problem I think, but it might be causing your problem.

Here's a thread with links to a couple more threads

IAC problems

 

[MrShorty]

Originally posted by eclipse5302
My 92 won't idle correctly when cold. Usually, when the truck is cold it should idle high (about 1200 rpm) until it warms up...like any vehicle does.

Have you verified that this is supposed to occur on this truck. I don't think my '92 has ever idled higher when cold, and I've never seen it mentioned in the repair manuals. My BII doesn't idle higher when cold. Is it possible that this isn't universally true?

 

[Maniak]

The '92 does have the IAC that does lift the idle during the start.

It is what allows the cold vehicle to keep running when cold (@ idle).

It also allows you to have the "no touch" start, you know, you turn the key (don't touch the gas) and it starts..

Without the IAC the motor won't idle when cold and the idle will actually be lower most of the time.. (you can check this by unplugging the connector from the IAC and watch what your idle does)

~Mark

 

[dogfriend]

Originally posted by Maniak
The '92 does have the IAC that does lift the idle during the start.

~Mark

I didn't mean that the 1st gen doesn't have an IAC in my post - but I can see how my wording might be interpreted that way.

What I meant was that the IAC issues seem to be really common on 2nd Gen (my 2nd one is now humming whenever its hot) but not as common on 1st Gen.

I think all multiport fuel injected Ford have an IAC and the IAC is responsible for the "No touch" starting as you said.

 

[Rhett]

eclipse, that doesn't seem like too abnormal behavior to me. If you're expecting the truck to sit there and idle at 1200 rpm for a minute or two after cold start, in all my experience with these vehicles, it's not supposed to do that. My friends have 93 Sport and 93 XLT and they don't do that and neither does my 94 Sport.

On _MY_ truck, it shouldn't idle high for more than a minute or so at startup. If it did I would be worried about vacuum leaks or bad IAC. For example, it's like this:
turn key...
engine fires...
idles at about 1200 rpm for about 10 seconds...
gradually idles from 1200 down to 700 (800 in winter) rpm over the next minute (2 mins in winter) or so...
once the truck is warmed up after about 10 minutes of driving (temp moves to middle of gauge) it will idle at 600-650 rpm which is normal warmed up idle for a 1st gen 4.0 OHV Explorer.

My truck is in perfect running condition too.

 

[Maniak]

Rhetts description is how our '92 X starts also, high idle, then drops after 10 seconds or so..

~Mark

 

[eclipse5302]

Well yeah, that's kinda what I meant it was supposed to do. My old 91 did that.

The thing is, when I start the truck it will go to like 800 rpm and instantly drop down to like 700 rpm. It doesn't even rev up a little after startup. This is a problem because when cold then engine will alomst die down when the rpm drops right away. If I hold it at like 1000 or so (like my 91 was) it will run fine when it idles down. Since the 91s are almost identical to the 92s I figured they should run the same as well. Hmmm...

Jason

 

[Maniak]

That sounds like the IAC motor to me. Starting @ 800 then dying isn't right.

My parts truck still starts (its a 91) and it does start, lift the idle to 1200 or so, then come back down..

You can tell if the IAC is problably bad by disconnecting the connector to it once the truck will idle by itself.. If the idle doesn't drop, the IAC is bad (or the circuit to it).

The symptom you are describing, start, stall, but idles fine once its warmed up is what our '92 did right after we bought it. I replaced the IAC and all was fine.

~Mark

 

[eclipse5302]

Anyone have an IAC motor they want to sell?

Jason