q45 idle question

[gloucester Q]

so, i just did my underplenum job--replaced most of the hoses, all of the fuel injectors ($$$--ouch!), gave what i could a general cleaning--the iac valve, maf, throttle body, and got it all back together with no missing parts and no leaks. out on the road, the car flies. great oomph and pickup--a noticeable improvement. in gear at idle, the car idles aroun 6-800 rpm, steady as a rock. so far so good. however, when the car is in park it's wanting to idle at around 1200 or so. i only got it back on the road this monday, so haven't had a ton of time to check and see if this happens all the time, but enough so far that it caught my attention. also, on starting (and i think it always used to do this anyway) it jumps up to ~2000 rpm and slowly hunts its way back to normal. is the high idle a sign of anything i could check or look in to? i am thinking of going to the local infiniti dealer at some point--between me and my mechanic (and this forum) we have maintained the car for the last 2 years without any deaership visits, so i feel like maybe i should go in and check that we've been on the right path and not screwed up anything. any comments? thanks.randy

[Q45tech]

When you totally clean IAC and throttle body turn the IAC bypass screw in to bottom then out 2.5 turns. The correct ~~750 hot idle [no ac in park]should be within +- 1 turn from that point. Most likely between 2.5 and 3.5 turns out.........if not, something is still dirty or you are not reading rpm correctly [interior tach is difficult to resolve at bottom].

What you want is for IAC solenoid [signal from ecu] to be at 10-15% duty cycle [90-85% of air flowing under closed TB and thru IAC bypass screw chamber] ---need Consult to read this.

[Q451990]

Also, make sure that your throttle cable adjustment isn't too tight. With everything warmed up the cables should have a couple MM of slack to prevent binding.

Heath

[gloucester Q]

thanks guys. tech-the bypass screw was out more than 4 turns, also checked the cables (they were good) and all is normal once again. thanks again.

[elwesso]

Just so you konw, if you dont mess with the IAC when you clean stuff, sometiems the idle will go up some... At this point, dont adjust it but leave it be, and eventually the computer will relearn the idle.....

[Q45tech]

The ecu can only decrease the IAC solenoid "on time" so much till it hits zero duty cycle then in reduces ignition advance to try to maintain idle speed ..............both are bad! As efficiency will suffer with reduce ignition using more fuel to maintain low idle.........not to mention emissions.

The exact IDLE duty cycle 10-15% sets the sudden off [lift] throttle from cruise dynamic range. And the step ups for AC and power sterring loads.

Don't force the ecu to do something to correct owner abuse.

[Infinitiguy19]

Since NICO search now rocks I took a gander (Funny word) at all the posts of the previous owner of my Q45.

I cleaned the EGR and tired to clean where the EGR mounts on the plenum and saw that its was clean, not clean enough to eat off (serious money required there) but fairly clean. I cleaned it some more and got what I could out of there and I also cleaned the EGR.

The above has nothing to do with the idle but goes to show how clean the plenum is despite last being cleaned in 2004. Thanks Mike

The Idle Air Control Valve was cleaned 2 years ago but its not spotless and a new gasket was used when cleaned. Thanks Mike

The Throttle Body was cleaned last year and was clean enough to eat off of (For free).

That said when I try to adjust the Idle Air Control Valve by pass screw to ~3.5 turns the idle goes to ~2000 RPM's. There are no vacuum leaks that I am aware of and the vacuum gauge read 20" Hg and was steady at that range.

So I ask please what could be the problem here?

Wes said it could be a small vacuum leak but I doubt it. Then again I do have a box of hoses from the previous owner. The previous owner didn't install those hoses because he said they looked fine at the time (Half a** ).

Please move to Q45 section.

[Infinitiguy19]

Can this be moved to the Q45 section?

[Infinitiguy19]

Can this be moved to the Q45 section?

[Q45tech]

Unfortunately many of the sealed [by red goop] adjustments on the typical throttle body have often been tampered with by mechanic types.

These set the dynamic range of the throttle lift off vs coolant temperature when added to the ecu use of coolant temperature as a fast idle warmup system.....Heaven Knows what the starting idle will be.

Why everything starts with a 10 minutes wait after cranking before idle rpm is measured.

[Infinitiguy19]

Well yet another thing we can rule out is a tampered throttle body. I had two throttle body's to start with from parts cars. I subjected both to hot water from the sink (I can't remember the exact temperature and the temperature sensing multimeter is down stairs.) On throttle body failed the test by remaining slightly open. The other one currently on my car passes because I poured water in the throttle body chamber to see if any leaked out and none did.

Now I know sink water isn't best thing to use but again I was to lazy to run down to the store and get some distilled water and then heat it up.

And I ONLY tried to adjust the Idle Air Control Valve when the engine was fully warmed up. So I can only surmise that I need to stop waisting time and replace the valve cover gaskets because oil is leaking on to two coil packs. And also do a BG fuel injector flush.

With the above done the car should run as smooth as it did 2 years ago if not I will be checking into the nearest mental institution.

[qship96]

Well yet another thing we can rule out is a tampered throttle body. I had two throttle body's to start with from parts cars. I subjected both to hot water from the sink (I can't remember the exact temperature and the temperature sensing multimeter is down stairs.) On throttle body failed the test by remaining slightly open. The other one currently on my car passes because I poured water in the throttle body chamber to see if any leaked out and none did.

Now I know sink water isn't best thing to use but again I was to lazy to run down to the store and get some distilled water and then heat it up.

And I ONLY tried to adjust the Idle Air Control Valve when the engine was fully warmed up. So I can only surmise that I need to stop waisting time and replace the valve cover gaskets because oil is leaking on to two coil packs. And also do a BG fuel injector flush.

With the above done the car should run as smooth as it did 2 years ago if not I will be checking into the nearest mental institution.

Never heard of baptizing a throttle body???????

[Infinitiguy19]

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