Another Idle Diag thread!

[5OF2k]

Good morning boys and girls!

I call upon the great wealth of knowledge here on GVR4.org, yet again:

Car:
'91 GVR4
built head
BC 272 cams
BC valvetrain
2gp/1gbr
SMIM
evo 560's
AEM EMS v1
converted to Speed Density with GM 5.1 bar MAP/etc
FMIC/etc
BRAND NEW FIAV
BRAND NEW FIAV bypass plate
Car idles normal for a couple of days, as it should right at or between 850-900 as set by the AEM, but then it decideds it doesnt like it there, and will idle steadily above 1500. It typically will "idle" between 1500-2000, sometimes higher.

Now, as I stated above, the car is on AEM EMS V1, and the tune is clean. I have a good read on the plugs, goos 02 voltage throughout under cruise, WOT, and closed throttle as expected. Both logs and plugs indicate it's not a tune issue(in my opinion).

I've recently replaced the FIAV due to a wandering/hunting idle, and it fixed it for a couple of days, then it came right back and started doing the really high idle (as mentioned above). So, I bit the $31 bullet and ordered the JMF blockoff plate, threw it on quick, and it idled fantastically for a few days, dead on, better than it has since I got the car in the first place. Now, all of a sudden yesterday, the extra-high idle is back, and reaaaalllly irritating the (BLEEP) out of me!

The car has no boost or vacuum leaks, as that was the first things I checked for, with the exception of a very minimal leak at the throttle body shaft seals (when I say minimal, I mean doesnt even register on the guage. I throw 26 psi at the system, and it'll hold for over 10 minutes, easily), brand new FIAV and blockoff plate. Also, my VIS screw is allll the way in, as in tight at the bottom of it's hole in the throttle body. So, in theory, it shouldnt even be running, let alone idling damn near 2k rpm, right?

The only thing I can think of, and what I think I'm going to try this afternoon once I get off work, is the Idle sensor switch. I just figured i'd post up here and make sure I'm not overlooking something completely obvious in my frustrations....?

Any insight, help, or ideas you can provide would be greatly appreciated. Im extremely picky in regards to my vehicles, and this idle issure is getting old, EXTREMELY quickly!

Thanks in advance, have a good one!

-Jake

 

[James]

Bad ECU bad ISC? (if you kept the ISC with the block off)

 

[5OF2k]

The blockoff doesnt include the ISC portion, but I didnt think of that either.... I may have to go look for a hyundai at the junkyard after work today too....

ECU is just fine, It's the AEM EMS v1. Like I said, I figure it's not a tune issue or related in any way to the AEM, other that some sensor not functioning properly therefore not giving the AEM the signal the car is trying to idle....

 

[James]

My mistake I forgot you had aem. Other than them two things I'm not sure.

Unless like you said its a bad sensor, TPS, maf or something.

 

[5OF2k]

Ah crap, that just reminded me. I should've put on there that it's converted to Speed Density also.

I might try to fab up a makeshift plate to go between the bypass and the Tbody this weekend, see if that helps at all having the FIAV completely blocked off, rather than simply bypassed to make it "think" it's always warmed up. the ISC motor itself could in fact be bad, I cant ever hear it move like I've been able to on cars in the past...you know, kind of a little buzz right when you hit the throttle after being at idle?

Appreciate the insight, keep em comin! lol

 

[toybreaker]

What's the iac count, both when it's at it's correct low idle and when it flares?



The biss being bottomed out points to an issue, possibly a mis-adjusted throttle plate. /ubbthreads/images/graemlins/dunno.gif

 

[5OF2k]

I have no idea what the count is, as the AEM doesnt give me info like that in the logs.... It's a whole 'nother ballgame than The Link or factory ECUs. If I hadnt bought the car with the AEM, I wouldnt be running it, FWIW. It's a steep learning curve!

What do you mean in regards to the throttle plate? It's opening and closing all the way, as it should, if that's what you mean?

 

[ktmrider]

Heard an improper ABS delete/disable can cause that issue. What's the status of yours?!?

 

[James]

I would replace the seals in the TB, and replace the biss Oring just for GP.

Clean the throttle body and make sure the plate is aligned properly.

 

[5OF2k]

Quoting ktmrider:
Heard an improper ABS delete/disable can cause that issue. What's the status of yours?!?



ABS is still on and completely functional

BISS screw has a newer o-ring on it, as well. As I stated above, the throttlebody shaft seals arent leaking enough to cause this, like I said it'll hold 26 PSI in a boost leak check for 10 minutes(charge pipes to 26psi indicated on guage, remove air supply and let it sit).

WHen I installed the FIAV bypass, I inspected the throttle plate as well since it was off, everything looks normal. Also, being as it's intermittent it also makes me lean more toward a failing or near failing sensor.

How would I go about testing the idle switch, or ISC?

 

[656of1000]

The idle switch is a simple on/ off switch. It either completes the ground or it doesn't, making it easy to test. Check to see if the switch itself is sticking, keeping the throttle from closing all the way. I've seen this happen before.

 

[5OF2k]

Got it figured out!!

A couple of the idle parameters were a tiny bit outside of the parameters i was seeing, most likely due to it being tuned in Cali origionally. Got them within tye proper limits, and it's good to go!

Appreciate all the input fellas, very much. Thanks again!

-Jake

 

Hey dude what are the value of the idle parameters..TY /ubbthreads/images/graemlins/confused.gif /ubbthreads/images/graemlins/shocked.gif

 

[5OF2k]

couple things to checck:

1) set idle feedback below value. If your idle feedback below value is too low, the ecu wont try to pull the car into the idle circuit. If your ide is high, set your idle feedback below rpm value to something a few hundred RPM higher than what it likes to hang out at. For instnace, if you're idling at 1500RPM, set the idle below RPM value to 18-1900.

2) re-calibrate the TPS volts. If the voltage at the tps sensor is lower than the 0% value AEM will turn off idle feedback which sets the car into the idle circuit. You basically want to set it so that it will idle at ~.5-2% TPS. If it's at zero it'll say TPS error and will often hang the idle high. There's a throttle configure wizzard menu itme that will have you close the throttle and WOT the throttle to set the min and max. Go to (configure>ecu setup>set throttle range) to setup the voltages. Then, With the car running you want to see the TPS at roughly 1.5% TPS. to set that go to (setup> sensors> throttle position sensor> options) then lower it a bit at a time by .5 until you get it to the desired setting. Beware, on the older software/v1 setups, changing the value manually you may have to enter the values more than once, and always hit enter after making a change, back out, and go back in to make certain they stay in the table as they should.

Typically, that's enough to take care of a weird idle issue, as I learned from Servion Tuning's owner Jeremy.