Firstly, search is singularly unhelpful on this subject! Problem: Some time ago I had a Unichip installed but the job was botched. One of the problems created was the loss of fast idle when the engine is cold. Since then the warm idle in neutral has been set at around 1200rpm to compensate, but this resulted in an idle speed in gear (auto, stationary) of around 900rpm. It was obvious that the idle speed was loading up the torque converter and the car would not travel at less than 50kph at idle without some brake application. Also, because of the "preload" on the T/C, the auto was reluctant to change gears unless I backed off on the throttle. Yesterday I finally got around to adjusting the warm idle (via the "thingy" valve on the back of the plenum, near the battery) down to 900rpm in neutral (750rpm in gear) , and things are so much nicer... no tendancy to creep excessively when stationary, gears change at much lower speed, and idle travel speed is below 40kph without any brake application. However (gotta love that word), when cold the engine idles in neutral at 600rpm and 450-500 in gear, if it doesn't stall. Question: Is there a relay/fuse or other device which may have been damaged that controls the cold idle speed, or is it purely mechanical... I read in some posts of a bimetallic strip which is part of the IAV (I think).? The current solution to the problem is to let the car idle until the operating temp is approaching "Normal" ie., 85deg. Thanks, from a long-time newbie!
Hi mate, I'm currently trying to track down some of my idle problems too, but I have made a few observations so far: The AAV (Auxiliary Air Valve) is what controls how much extra air on top of the IAV (Idle Air Valve) to let into the engine at any given point of time. This means that when adjusting the IAV (the screw "thingy" as you call it),it is not accurate at all because the AAV is still letting a little more air in. The correct way to adjust your Base Idle, is to use Consult/Dr300ZX etc to turn the AAC off, so it is just the IAV letting air in. This will enable you to set the correct idle using that screw thingy(~720-750 depending on car model), then turn the AAC back on to compensate where required. Through Consult / Dr300ZX you can actually see how much extra air the AAV is letting in via a percentage. The appropriate idle percentage is between 15-25% at warm idle by memory. If you find that your AAV reads something like 30% or more at warm idle, you may have a sticky AAV valve. This would probably mean that at cold that value could be even higher, causing a real high idle (and a real annoying auto creep while "stationary"). I have noticed in my zed, that on an ultra cold day, on first startup it would idle at around 1700rpm, but when I pump the revs a little bit (only to 2-2.2k, the revs would slowly descend, faster than if I were to just leave it idling. This says to me that maybe my AAV valve is old and sticky, so as I pump the revs it slowly loosens it up. The other observation is that when you unplug the big grey TPS connector (after cleaning the TBs), the base idle changes yet again as it recalibrates everything. And the final observation is something that I haven't been able to figure out: Sometimes at cold idle the idle would actually hunt around, and every time it raises the idle you can hear the fuel pump priming (well buzzing, whatever it's doing). But that seems to be a different issue, so I wouldn't go down that path until you're sure the rest of the idle system is OK. Sorry for the essay lol but I figure if I'm gonna document zed idle system observations, I might as well do it somewhere relevant lol. Cheers Greg.
One step at a time Doug.... The air regulator (bimetal strip thingy) controls cold idle, electrical current actuates the rotary valve causing it to slowly close, reducing the idle. The AAC solenoid ("thingy" valve on the back of the plenum, near the battery) is the ECU control valve for warm idle and pulses on/off to regulate idle dependant on information supplied to the ECU by other sensors. When adjusting warm base idle with the idle screw, the AAC solenoid should be disconnected (via datascan or pull the yellow connector), and in your case (NA auto) it should be 720+/- 50rpm in NEUTRAL. Using a multimeter test resistance on the following : Air regulator : 70-80 ohms AAC : 10 ohms If you put 12V across the AAC solenoid you should hear it click if functioning but the air regulator doesn't make any noise. It's a process of elimination. Hope this helps get things sorted.
Don't forget the other things... The IAA (Idle Air Adjust) on the IACV (Idle Air Control Valve) shouldn't be adjusted until two other conditions are met... 1. The car should be at a normal operating temperature 2. Air conditioner should be off. That's on top of any other conditions (Consult, TPS etc)
2nded on the Air Reg as the culprit the unichip install may have eliminated the ECU control of the Air Reg valve. Worth checking with the unichip installer / or others here with a Unichip, if it supports cold start control via the air reg. If your cold start was OK before the unichip install, then thats the best place to start diagnosing. If any work has recently been completed at the top/back of plenum then as K-Zed chicken legs said, the Air reg wiring plug may have been disturned and needs cleaning and retensioning or better still replacing.
