High Idle

[Aeroking]

I know what your gonna say, but hear me out.

I've checked the usual suspects.

My truck is idling at 1800rpms. Pullin a steady 19inHG of vacuum.

- The vacuum system holds 19inHG solid, long after the engine is shutoff.
- Engine is brand new, new gaskets, plenty of sealant around intake.
- Vacuum lines in good working condition
- New EGR valve
- Resetting IAC, counts are around 35, then promptly drop to 0 counts.
- IAC has about 1200 miles on it (NEW)
- TPS is at 0% and is functioning properly, and the throttle blades are in good condition.
- 19inHG of vacuum at the 3bar MAP sensor
- I've sprayed starting fluid around the intake seam areas, and on vacuum lines. No leaks
- Its a custom grind cam, pretty steep.


Possibly a timing issue??

when the Tan wire is disconnected the truck idles at 850rpm, but when i connect the Tan wire, it jumps back to 1800rpms...

 

[sy#2921]

Re: High Idle

First stupid comment would be have you put it on a timing light to verify actual timing? 0 with the tan wire disconnected and the matching tunerpro with it connected?

 

[Aeroking]

Re: High Idle

Tunerpro reads 21degrees adv. at idle (1800).

PCV valves functioning.

cam isnt degreed, it's straightup.

 

[Syclone#892]

Re: High Idle

Just throwing this out there for an idea but I had a similar problem with my old prelude. I had installed a bunch of parts including a ported throttle body. Either the tps sensor was bad or there was something wrong with the throttle body, I swapped a stock throttle body on and never had a problem after that.
Would have just changed the sensor but can't buy just the sensor on the honda and it was permantly attached, so stupid.

So all in all I would try swapping the throttle body.

Good luck!

 

[91blazins10]

Re: High Idle

Idle stop screw turned in too far?

x2, Brandon did you ever check this?

 

[Aeroking]

Re: High Idle

wouldnt being "out" too far, cause a high idle.

 

[sly dvl]

Re: High Idle

Have you tried adjusting your TPS yet? I noticed it was sitting at .59 volts during the tuning session.
IMO - that's too high. In my experience MOST GM's like to sit around .36v - .48v
I know that on some GM's (old skool, 80's & 90's) once the ECM saw a TPS above .56v it no longer attempted idle strategy. I realize this kind of conflicts with you IAC counts at zero, but if they're sitting at 30+ it's not trying to bring down the idle.
Back off your idle stop screw & if that's not enough you can usually get another .04 - .06 drop bu loosening your TPS, shifting it to the extreme and then tightening it again.

 

[91blazins10]

Re: High Idle

wouldnt being "out" too far, cause a high idle.

yea lol I just read idle stop screw, we all know what Dave ment

 

[sly dvl]

Re: High Idle

yea lol I just read idle stop screw, we all know what Dave ment

Not sure I understand the confusion but turning it "out" will close the throttle plates, reducing the air getting around them & lowering the TPS volts.

If you're getting 19" @ 1800 RPM then you'll probably get 17" once the idle is down where it's supposed to be. Higher RPM ='s higher vac.

 

[91blazins10]

Re: High Idle

If you tighten the screw it will cause a higher idle, if you loosen the screw it will close the blades enough for the iac to adjust the idle.

 

[skipztt]

Re: High Idle

Have you tried adjusting your TPS yet? I noticed it was sitting at .59 volts during the tuning session.
IMO - that's too high. In my experience MOST GM's like to sit around .36v - .48v
I know that on some GM's (old skool, 80's & 90's) once the ECM saw a TPS above .56v it no longer attempted idle strategy. I realize this kind of conflicts with you IAC counts at zero, but if they're sitting at 30+ it's not trying to bring down the idle.
Back off your idle stop screw & if that's not enough you can usually get another .04 - .06 drop bu loosening your TPS, shifting it to the extreme and then tightening it again.

i agree, on my GN the voltage on the tps should be around .45, or something like that..lol. i would play around with that.

 

[Aeroking]

Re: High Idle

doesnt the truck make more vacuum at low RPMS, and less vacuum at high RPMS?

so if i'm making 19in at 1800rpms, i should be making well over 20in at the stock 850rpms?

 

[turbodig]

Re: High Idle

i agree, on my GN the voltage on the tps should be around .45, or something like that..lol. i would play around with that.

You can't adjust a TPS on a SyTy. Furthermore, you don't need to, since the ECM automatically "zeros" the minimum reading.

 

[turbodig]

Re: High Idle

0 IAC counts means that the ECM can't lower the idle low enough, but it's trying....

Idle stop screw turned in too far?
PCV valve malfunction?

and: 19" HG w/ "custom grind cam, pretty steep"??? Seems too high. Did you degree the cam, or are certain it didn't get installed retarded?

This is the direction I'd go. With the plates closed flat, and the IAC closed, there's *got* to be a leak someplace. Motor won't run without air.

 

[sly dvl]

Re: High Idle

doesnt the truck make more vacuum at low RPMS, and less vacuum at high RPMS?

so if i'm making 19in at 1800rpms, i should be making well over 20in at the stock 850rpms?

Nope, you've got it backwards.
Vacuum is proportionate to Load & RPM. Because you're idling at 1800 RPM & there is no load on the engine your vac. readings will be high.
However, when you ad a load (like putting it in gear or accelerating) then the vac decreases.
Idling at 1000 RPM vs. in gear and loaded at 1000 RPM you'll get two very different vacuum readings.

 

[Aeroking]

Re: High Idle

Nope, you've got it backwards.
Vacuum is proportionate to Load & RPM. Because you're idling at 1800 RPM & there is no load on the engine your vac. readings will be high.
However, when you ad a load (like putting it in gear or accelerating) then the vac decreases.
Idling at 1000 RPM vs. in gear and loaded at 1000 RPM you'll get two very different vacuum readings.

thanks bud. :tup:



i'll get 2 new PCVs tonight, and replace the ones on there.

crossing my fingers that i dont have to pull the intake off.

another thing is i dont have the front PCV hooked to anything. the front one just relieves crank-case pressure if i'm not mistaken. i have a breather on that PCV. and the rear PCV runs factory back to the TB port.


could it be timing?. the initial timing is at 0deg. And with the wire connected, TP reads 20~22deg advanced at 1800rpm idle. seems pretty steep. would chamber scavenging cause a low vacuum effect.

 

[sly dvl]

Re: High Idle

Your timing is an output, not an input. Providing your base is set correctly then I'd ignore the readings from your Tuner Pro until you get that idle down.
Back the idle screw out until it no longer touches the throttle stop, then go in about 1 turn. That's where you need to start.

If I understand this PCV system correctly one works under vac. up to atmospheric and the other works under boost conditions. Unless the PCV is the wrong one or the lines are leaking vacuum it won't have an effect on your idle.

Turn the damn screw already!!! :rotf:

 

[Aeroking]

Re: High Idle

i bent the tab on the linkage bracket to get the same effect as screwing the stop back, and no difference.

tonight, i'll plug in datamaster, and see what how much my MAP sensor is reading. might have a bad MAP sensor.

 

[WyoSyclone]

Re: High Idle

tonight, i'll plug in datamaster, and see what how much my MAP sensor is reading. might have a bad MAP sensor.

When you have DM hooked up, be sure and record engine temp, MAP, AFR, O2 voltage, IAC counts, and spark advance. If you're getting a stable idle with the timing connector disconnected it would seem you may have a bad ignition module.... looking at the above will probably help nail it down.

Also, how long has the truck been running when this is happening. My Sy will idle at about 1500 for about a minute when it is cold, then gradually go down to 850.

 

[sly dvl]

Re: High Idle

When you have DM hooked up, be sure and record engine temp, MAP, AFR, O2 voltage, IAC counts, and spark advance.

...and TPS Voltage... TPS % is a calculated value, TPS voltage is an actual value.