I start by saying: If you try this fix, I am in no way responsible for any damage you may do to yourself or your vehicle resulting from this. It worked for me and continues to work great. Please try this at your own risk!


I drive a 1998 Discovery II 4.0L Le with advanced Evaps.





I have recently been having a issue with VERY HIGH idle. Usually around 3000RPMS. After trying to trace down the problem by way of every sensor, every component, cleaning the throttle body spotless, and finding no vacuum leaks, my only conclusion is bad VALUES in the ECU for the IACV.


I understand a TESTBOOK reset may solve this. but as most of us find, a Testbook was not readily available to me.


so...to my fix.
I found that the IACV was still functioning, along with all other sensors and components. So I figure the ECU for some reason has corrupt VALUES for the IACV. (Ex. its a stepper motor with values ranging from 0-255 to my understanding. I felt as though my ECU would only send a value in the range of 200 or so, giving me a VERY high flow of air into the engine. Though, it should reset to a value closer to 0-20 while running and adjust slightly while running according to electrical load on the alternator.)


I then got under hood]. I disconnected the Negative (-) lead on the battery so I could control the power from there by leaving the key in the (ON) position. I removed the IACV but left it connected to its plug. by connecting and disconnecting the battery I allowed the IACV to extend past the point than the ECU would let it while installed. To a point closer to a NORMAL IDLE SETTING. I then fitted the IACV back into the slot it goes in. I made sure to start the engine (while warm already) and find a position with the IACV inserted that the engine would idle smoothly (after adjusting the THROTTLE CABLE TENSIONER.)
My Disco now idles perfectly. I idle a little high in park or neutral at about 980rpms. While in drive or reverse I idle a smooth 725rpms. If I turn on the headlights, the A/C, my stereo with subs, and turn the wheel sharply I drop to around 600rpms. Plenty to keep the engine idling smoothly. Starts in cold weather require a little pressure on the gas pedal for about a minute. but as soon as it begins to warm up it idles beautifully.


To my understanding the IACV mostly operates when the engine is cold to help CHOKE and keep the engine running, and to help steady the idle during electrical intense operations. such as: headlights, braking, deceleration, radio, a/c, power steering pump, etc...


So...my conclusion is the IACV is not necessarily needed. As my Disco runs great with a permanent setting on the IACV. its been over 2 weeks since I did this. No CODES have been thrown, and it runs like a dream now.

 

interesting.. 98 d2 interesting, also

 

I should have noted that this started when my hood liner fell apart and completely clogged my airbox. I imagine this caused my ECU to learn values for the bad airflow and was compensating by opening the IACV all the way. Apparently these values can't be unlearned, only reset.

 

You messed with things instead of fixing it correctly

Install of. New IACV requires ecm reset plain and simple,: idle is set at 700 rpm in park not 8 not 9 messing with throttle stop/ cable etc is not fixing it it is messing your engine up worse

I have been through this know what I am talking about you tried to put a band aid on a severed limb it will not work for long and get worse just my .02 so someone else does not follow that and screw up their engine

I am referring to d1 gems there is no d2. In 1998

 

there is a 98 GEMS D2. it was made in the last quarter of 1998 though it was not introduced to the US until 99. http://www.roverparts.com/TechTips/boschvsgems.cfm. Though this page says 99-04 I assure mine is 98.


i did not replace the iacv. also..an iacv install does not require a ECU reset. a little reading can find this info


it is not messing anything up..a static IACV setting is done a few ways. with idle plates and others have even fashioned their own manually adjustable idle plates.

www.autoshop101.com/forms/h60.pdf
This link is for Toyota. But explains how iacv works.

 

If anyone is interested. I found another site where a few guys are talking about this. A couple of them actually described fashioning their own manually adjustable IACV plugs or plates. They are talking about the P38 GEMS models.

http://www.pistonheads.com/GASSING/t...p?h=0&t=488313