My '99 Ranger 3.0L is idling high at 1100rpm. After reading around on several forums the culprit is generally the IAC. So first off I drive around to get the engine up at normal temperatures, come home and pop the hood. I then unplug the IAC.... and the engine sounds amazing! Idling smoothly at 550. So out I get to blame the IAC and I clean it with some electrical contact cleaner and some qtips to make it all nice and shiny. Installed it back on the truck, turn it on and it is still at 1100. Meanwhile as it is running I unplugged it once again and the idle drops down to 550-600, then I plug it back in, and on comes the CEL. I turned it off, left the negative battery terminal unplugged for 10+ min, turned it back on and the CEL is off (good news), BUT the idle is still at 1000-1100. I mention 1000 now because it sits a little lower, I don't know if it's affecting me like a sugar pill but it seems to be that little bit lower. Any ideas on why it is still idling so high?

 

The port that the pintle on the IAC seats into may have some crud holding it open.
May have to clean the throttle body.

 

What is the pintle? There were the 2 ports on the IAC. The spring side wasn't too dirty but I cleaned it, the other side which had the sensor I cleaned with the q-tip. I put my finger inside the sensor side and was able to lightly push the valve down towards the spring. It didn't feel too restricting.

 

An update to this thread. I took some photos of what the IAC looks like. Should the valve compress the spring much? I can move the valve slightly towards the spring but only 1/2cm or so.

Edit: I took the IAC off two more times today and all 3 times I have had it off the valve is sitting in the same location with the plunger roughly a 1/2cm open letting air pass onto the throttle plate. It never has been fully closed. I also cleaned it more since the pictures with carb cleaner, keeping it away from the sensor end but removing almost all the soot.

Sensor side of IAC.


Spring side of IAC.


IAC viewed from underside.


IAC viewed from top. The cap is not plastic, it is steel.

 

I also have been having a higher than normal idle. Ive cleaned my iac (did nothing for the idle), but havent voltage tested my tps yet as my voltmeter is not with me (im out of town). I suspect a vacuum leak and will be checking for one soon and will post my findings later next week. even when i unplug the iac my truck still idles around 700... and while driving normally the higher idle is making slowing down harder, as well as a goofy downshift into 2nd and 1st due to the higher idle. in park my scangauge says 880 to 900 for an idle...

M

 

the only reason why the CEL went off is because you disconnected the battery...that reset the ECM...after you drive it for a little while the light will come back on if the problem still exists

 

The only reason it came on was because of the IAC being unplugged. I've also put on another 30km since then and no light.

It idles at 1000 in park with the A/C off which is still high. I am thinking like OTRtech and will replace all the vacuum lines.

 

you might not have reset the monitors yet...hope you get the problem figured out

 

What do you mean by the monitors? I'm not familiar enough with the terms

Hold on a second... I just had a second of wisdom, so I think. How could it be a vacuum leak if when the IAC is unplugged the idle is at 550, which is very reasonable. If it were a vacuum leak would't the idle still be high?

 

there are emission monitors that keep an eye on the emission items in the car...whenever you cut power from the ecm they are reset because they lose the memory and it takes a little while for them to reset

 

Today, I pulled off the connectors off the IAC, TPS, and MAF, sprayed them with electrical contact cleaner, and put some dielectric grease on. Still no change. Idle is at 1000 with A/C off and in park. To understand the problem as well I don't get the rough idle others get with a bad IAC. It idles smoothly but obviously loud at 1000, and when the IAC is unplugged it idles smoothly and quietly at 550.

 

I may think i have a vacuum leak after reading through all these posts. I unplugged my IAC today and my idle still remained around 750 (via my scangauge which i assume is accurate..?) Upon re-connecting the IAC my idle spiked and then returned to 900 at idle in park with ac unit off. Also, is it possible to hear a vacuum leak while driving? like going 55 in 4th (auto trans accelerating out of O/D) < in this scenario i can sense or hear the engine sucking air more than normal ( just through the intake) like a brake booster line when you unplug it to seafoam... The engine runs fairly strong and with my 31 inch duratracs i can hold o/d at 60mph but forget any type of speed increase while holding o/d at 60 unlesss going down a hill haha.

I will post what i find this week when i get it in for a smoke test on my vac lines.

M

 

Sprayed around the vacuum lines today with some carb cleaner and there appears to be no leak, This is definitely becoming frustrating. :(

 

so, my truck is running great now...
I put in a vacuum gauge (glowshift) and saw a steady 17-21 inHg at idle, and proper vacuum readings throughout driving, except when burping the throttle and letting it drop back to idle i never saw the gauge drop to 25ish and then back to 17-21 it just dropped to 20 and sorta stayed there, i have a feeling this means my rings are less than good... anyways back to the idle,

I cleaned the mother out of the IAC and the throttle body, like i actually took the whole assy off and went to town. There was a ton of garbage on the plate and bore, special coating my ***! so i cleaned dissregarding the warning about the special coating and let it all dry for roughly a half hour before re-installation. After i re-installed it i set the idle screw using a .002 feeler gauge and a half turn in after it just touched the feeler. I backed it off of the half turn just a bit and was getting .82 volts on the TPS at idle position, so good there and 4.59 v at WOT.

Fired the truck up and drove it around town letting the comp relearn the new idle screw location. 20 min later the truck idles in park at ~800+ and just below 800 in drive at a light. Perf! doing an oil change and using auto rx today :) truck has 140k on it. cant wait to see what happens when i tear into that oil filter after 3k with auto rx.

cheers, i'll check back on the thread to see if you guys try this out with the TB and IAC, I mean reallllly use a toothpick to scrape that crap off, especially inside the IAC on that plunger.

M