Low idle when cold

[Bray D]

I searched and couldn't find anything (on the first page anyways ). Everything I found was for high idle.

Anyways, upon first startup it idles low, like 6-800rpm until the engine gets up to temp. Once its at temp it idles fine around 1k. Ambient air temp here is ~50-60 degrees.

New plugs, wires, coil, and IAC. All less than 1 week old.

97 explorer OHV 4.0.

What say ye?

edit: Fuel pressure at the rail is good. Vacuum is good. New fuel and air filter. TPS?

 

[wahlstrom1]

Mine used to idle that low... is it stumbling or still running smooth?

 

[Bray D]

Still runnin good. Just idles low until its warmed up. No big deal really, but if I can remedy it I will. It idles low enough it'll die if I don't blip it a couple times, then it'll hold on its own - low until it warms up.

 

[wahlstrom1]

Sounds like it could be a vacuum leak, could try cleaning the throttle body and checking the holes in the throttle plate. Also, a sticky IAC valve could cause the issue.

 

[Bray D]

I had the codes pulled when it was running like ass, threw one for the IAC so I put a new one on it. Didn't make a difference. Went to have the codes pulled again to see if anything else came up (had em pull em while the truck was running, too), and IAC still came up even with the new one on there. Not sure if its just cause I didn't undo my neg. battery terminal or what.

Pulls a steady 20lbs vacuum at idle. Same a higher rpm. If I give it a quick punch off of idle, it drops to 0 until it settles to idle again then it bumps back up to 20. If I hold it a higher rpm and just let go so it settles to idle, the vacuum jumps up to 23-24 then settles back to 20 at idle.

I could check the TB though.

 

[wahlstrom1]

Possible IAC wiring difference? I'm not too keen on electrical, so I don't know if you would have had to repin anything involving that during the swap...

 

[Bray D]

I don't think so. I think that portion of the harness is 'stand alone' with the ECU. The new IAC I put on it had the plug rotated 90 degrees from the one I took off though haha.

 

[wahlstrom1]

Funny enough, so did mine when I replaced it on the UA trip. I spent 4.5 hrs in New York City rush hr traffic on July long weekend (Independance day) listening it make Jetson mobile like burbling and hoover vacuum noises, lol. It was replaced as soon as I got to the nearest parts store.

 

[Bray D]

Jetson mobile like burbling

Perfect analogy. lol

Sooo, anything else that would cause this thing to idle poopy?

 

[wahlstrom1]

You still running an auto tranny computer?

 

[Bray D]

nope. Got an ecu for a 97 explorer, OHV 4.0, man trans, but it had all the extras (power windows/locks/sunroof/etc).

 

[wahlstrom1]

well....I'm outta answers. Grab a spare throttle body from a wreckers and drill an extra hole or two in the plate. Maybe the IAC will compensate for it once it's warm.....

 

[Bray D]

I think I'll start by pulling it of and givin it a good cleaning haha. I do have another one though, from that 94 4.0 I was gonna build.

 

[Sasquatch_Ryda]

6-800 is perfectly normal, and is the target idle RPM.

 

[Bray D]

Should it idle up when its cold? My 3.0 always ran a little high until it warmed up. Like 1200-1500. When I first start this engine it will die if I don't keep it alive with the throttle for a few seconds, then it will idle at 6-800, then after driving it for a while it idles right at 1k.