Idiling

[donsz34]

I have a 93 z34 when i start it up when it is cold out the rpms jump up to 2k and fall rite down to 1k . Is that normal ? I have had the car siting in my driveway for about a month. now im going to put it on the road tomarow . Also i put a new iac motor on it. I would start it up and the idle was so hi it would kick the rev limter on but it wouldnt do it all the time . With the new iac i havnt had any problems with it .
Thank you for any info Later, Don

[Lyle's GTP]

Then jump than fall immediatily? Like: Crank.....Fire....Rev high..............then normal. All in about 2-3 seconds? If so I think it's normal. I think the car does this to give the car more power to start the cold engine. Kind of like over compensating.

Lyle

[donsz34]

Just like that . Starts spikes up then falls down fast .

[Lyle's GTP]

That's normal, unless we have the same problem, but my girl friends car does the same.

Lyle

[xtremelumina92]

sounds like intake gasket to me

[dykz34]

That's normal. That's the IAC holding the RPMs to allow the engine to warm up.

[Anonymous]

Yes that is normal as part of the IAC and the car's "choke" if you will.

[brian89gp]

Yea, if you do manage to disable the rev up, it will make the car almost unstartable without the use of your right foot.

[5speedz34]

Yea, thats normal if you want me to look at for you I have no problem doing that.

[Juglenaut]

I would replace the upper/lower intake gaskets to be on the safe side.

The ECM will compansate to a point and it may just have been the old IAC was bad to a point that the ECM could not adjust it to where it needed to go. A new IAC most likely gave the ECM the right parameters without faulting.

I would replace those gaskets, but that is me.

How I tested my IAC:

Removed it dah
plugged the hole with a rubber vial stopper with a air hole in it that is releasable.
While holding the IAC firmly over the valve/germ gear making sure it would not self destruct.
Had a friend start the engine and let it idle untill warm, measure idle length plugged
Releasesed the air hole in the vail stopper, measured legnth.
Had friend pulse rev to 4 grand no higher, tried to see it actuate and take measurements.
Had the RPM held at 3grand vail stopper vent plugged, and measured, do the same for unplugged.
Let the car sit over night.
Start the engine (again make a friend start it) while holding the IAC, quickly measure the difference from the last position to cold compansation while the vail stopper is plugged then release the vail plug vent and measure the difference.

This sound wierd and really stupid I know, but the point is that I found if you minus the change of cold compansation plugged and unplugged that yields the distance of change in cold. Then the measured values while it's running warm plugged Idle minus the unplugged and take the measurements from the 3k Idle plugged and unplugged and average it with the Idle value. Lastly minus that Idle value from Cold compansation value and it yields the amount of valve clearance at idle needed at the normal IAC stop from idle relearn enable.

I think I came up with .115 of an inch and just about 1.075 inches extended from the base of the actuator when IAC is at neutral or zero steps the IAC should never close all the way reasons for under compansation. This is according to my car and I did, at first, have had the phatom stalling and high revs at cold start, I replaced the IAC and the upper/lower intake gaskets now no stalling except on really hot days.

Your results may vary, but I recommend leaving some gap on the IAC valve to full close it should not close at any time thru RPM range unless it is under compansating and usually the ECM will only under compansate by 5-10 steps before throwing a code and will throw a code if it over compansates relative to temp by 50 or so.

[joey b]

dude, I have no idea what you just said

[Juglenaut]

Just don't make the IAC a tight fit when putting a new one in. It is said that the length of the IAC motor valve from the base of the valve to the base of the motor assembly to be 1.125 inches 1 1/ 8. Most new IAC are set to zero Steps Neutral. This is a universal length designed to meet most engines parameters, but I found that a gap is needed of less than 1/8 of an inch more like 1/10th on my 3.4L.

I did try the 1 1/8th set-up and the RPMS were unsteady and dropped below 800 RPM when coming off rev and died occasionally. My car is a factory manual and auto vary some, but I would still leave about 1/10th of an inch gap on the IAC. Normal RPM on a auto is about 600-700 warm/hot idle and should not dip below this on a hot run in gear or after revs. Normal cold compansation is about 1100 rpm on autos, cold start hold 2k and then drops to 1100 untill warm enough for warm idle.

You must adjust a new IAC to meet the legnth given in the instructions, but like I said I had better results leaving a small gap. Never push the valve in on a new IAC it throws the neutral position off and then you have to either bring it back or do the mumble jumbo that I posted earlier to find neutral within a few steps.

Step Zero= valve closed neutral

Most IAC are suposed to be set ay zero when new, however sometimes this is not the case.

If you remove the bolts holding your IAC on with an engine at hot idle it should not push itself out of the throttle body or push itself out at anytime thru the RPM range on a normal engine without any vac or intake leaks. If it is improperly set it will either show High RPM at 0% angle throttle (stepped to open) or push itself out at idle even a little bit is bad. Again it should not make a complete seat againt the valve openning in the throttle body.

If you are going to check the IAC position at hot run thru RPM range, make sure you have a friend start the engine or the IAC will self destruct if the IAC is set wrong.

[pocket-rocket]

I would put my 2 cents in and say it's normal, but it has already been addressed many times over now :P