Low idle when warm

[jman101]

My 99 explorer (v6 SOHC) seems to idle really low when warm. When cold, it will idle at around 1000 rpm however once it warms up it drops down to about 550 rpm (checked with OBD scanner) at idle. Also, if I start the engine while it's already warm it revs up to 1000 rpm then drops down so low that it almost stalls out (lights dims) and then settles on 550 rpm. Other than that the car runs fine and seems to start fine (never had it actually stall out on me at start, just seems to come very close). Any idea where I should begin looking for problems?

 

[koda2000]

When I bought my '97 SOHC back in April of last year it also idled too low (around 500-550 RPM). There is no "idle speed adjustment". The idle is controlled by the PCM and the IAC. However, there is a throttle plate stop screw on the right side of the TB. You don't want to turn this screw out as the throttle plate can stick closed, but I found by turning the screw in slightly it increased my idle from about 500-550 to 650-700 RPM. I thought the PCM might see this and try to turn the idle back down via the IAC, but it's been 10 months now and the idle ha sremained where I set it.

Before I did this I had cleaned the IAC, TB and the MAF, but that made no difference in my idle speed.

I think the 1000+ RPM is normal for the SOHC engine. It's referred to as the "starting flare". I don't know why the SOHC does this. To get the oil pressure up for the chain tensioners maybe. Both of my SOHC's did this and I've never cared for it.

 

[my98nnj]

550 is pretty much where mine idled for all its silky smooth life. Why do you think that's to low?

 

[koda2000]

550 is pretty much where mine idled for all its silky smooth life. Why do you think that's to low?

550 just feels to low to me. 700-750 seems more normal and it should help to keep the oil pressure up a bit..

 

[2000StreetRod]

commanded idle speed?

. . . When cold, it will idle at around 1000 rpm however once it warms up it drops down to about 550 rpm (checked with OBD scanner) at idle. . .

Use the scanner to read the commanded idle speed and compare that to the actual idle speed. If they are significantly different I suggest cleaning the IAC valve. If they are about the same then read the engine coolant temperature and the fuel trims. The AFR should be rich when the engine coolant temperature is cold.

 

[Flash]

I think the 1000+ RPM is normal for the SOHC engine. It's referred to as the "starting flare". I don't know why the SOHC does this. To get the oil pressure up for the chain tensioners maybe. Both of my SOHC's did this and I've never cared for it.

I thought 550rpm was normal.
That's where mine is and sometimes when I stop at a red light i think the engine has stalled it's that quiet and smooth.

That start up flare is to boost the oil pressure and I hate it.
My current LTD with the previous engine used to flare much higher than that and with a rattly chain it used to really bother me.

I found out if you stand on the gas pedal before you start it, like the old automatic choke system, it doesn't flare as much.

My current engine doesn't flare much and I have no chain rattle so it doesn't bother me at all.

 

[Flash]

The idle is controlled by the PCM and the IAC. However, there is a throttle plate stop screw on the right side of the TB. You don't want to turn this screw out as the throttle plate can stick closed,

You don't want to do this.
Adjusting the throttle plate will will put the adjustment relative to the TPS out and you might have some off idle issues because of it.

550 RPM is normal you just have to find out why it drops below that.

As Koda said, clean the idle control valve, the MAF and the throttle body and see how you go.

Do that stand on the gas pedal thing to see if it stops it flaring so much.

 

[2000StreetRod]

desired idle speeds

I looked at the stock tune for my 2000 SOHC V6 Explorer:

Idle Speed Neutral = 656
Idle Speed Drive = 624
Max Allowed Idle Speed Drive = 976
Idle Speed Adder with A/C on in Neutral = 0
Idle Speed Adder with A/C on in Drive = 0

ACT = air charge temperature = intake air temperature

ECT = engine coolant temperature
If the engine has set overnight and the ambient air temperature is 30 deg F then the engine speed at start will be 656+72+304=1032
There is a time from engine start for the above to apply. After the time is reached the following applies.