Need help with diagnosis

[olds443]

Car runs great but can't seem to get the idle rpm down.
About a month ago my idle rpm shot up and I took off the IAC only to discover that the little cone (pintle) on it had unscrewed. IAC #s were out of whack. Repaired and replaced and all was fine. Now the idle is high and the IAC counts drop as it settles into idle to zero. If you give it any throttle the IAC counts do rise, but hot in park they drop and sit at zero. I took the IAC out and cleaned it and the bore, put it back in and no change. This thing is only about 6 months old.

I have been reading old posts on here and finding similar problems and trying eveything to see if that changes anything but all is still the same.
I even reset everything twice but can't get the IAC to stay above 0 at idle.

Scanmaster readings at idle are

AF = 9-10 (usually at 9) Also seems to fluctuate with fan. If fan kicks on then it raises and so does idle.
Lb= 31-38 (moves to 52-56 in drive)
bat= 13.2
int= 128
bl=142
clt=162
ats= 81
rpm= 1650 (drops down to 850-950 in drive)
TPS = .44
IAC = 0 (does move with throttle; when starting cold it is at 176 then drops down as it warms up) Idle also sucks when first started cold, sometimes stalls, apply throttle for a few seconds and it idles good.

Vaccum on my Stewart Warner Boost/vac gauge shows 12lbs which is what it has been before. I was told it has a non-stock cam but I don't know the specs.

I have checked and blocked off the brake booster at the vac. block, the egr solenoid and changed PCV to an Ac delco. No change in how it runs or the idle.

I did unplug the MAF and it ran worse (stumbled, etc) but the AF #'s came down as well as idle rpm. Tap test revealed nothing.

I changed my coil pack out with another good one I had and it changed nothing.

I reset the IAC as stated on GN Tytype.org as well as Vortex Buicks and even tried the old Buick Manual way. With the IAC unplugged it did throw a code but idled well, really low, 450-500 rpm and the AF was at 6 like it used to be.

I read something about throttle body seals leaking, could this be my problem?
or maybe it's my IAC?
MAF? It still reads up to 255 if I nail it (That was fun keeping an eye on the gauge while doing that

Anything I may have missed? ANyone else seem to have the same problem?
I have set the IAC successfully before so it's really got me stumped.

 

[85HOT-T]

Maybe your throttle boddy plate is open too much? How far is the screw in?

 

[olds443]

No, I played with it so much trying to adjust it, the best idle I could get is with it just barely resting on the throttle blade arm. The tip of the screw barely protrudes

 

[85HOT-T]

hmm well 0 iac counts usually means vac. leak, especially with your idle. Wierd that it drops to normal rpm in drive. Gotta think ablout this one.

 

[olds443]

Been doing lots of thinking and searching. I did plug off all the ports on the vac block also, but again no change. BLMs have been higher for awhile since I got a new chip but it ran and idles fine. I also pulled the egr and tightened it back up good with some gold permatex. Had a slight effect.

 

[olds443]

ttt
still need help

 

[85HOT-T]

hey maybe maybe your egr is leaking?

 

[WHEEZER]

I would pull and clean the EGR also. It has a pintle set up similar to the IAC and can clog up with carbon too. Then step by step as outlined in the TR or Vortex site adjust the TPS and IAC untill you get the right settings. Also check for vacum leaks. Just my 2 cents.

 

[bison]

If your car still idles fast and the throttle blade is nearly closed and the IAC is closed, then it has to be a vacuum leak. Have you verified that the IAC pintle is actually moving? The IAC counts is only what the ECM is telling it to do, not if its actually sealing off the air bypass.

 

[SloGN]

If your car still idles fast and the throttle blade is nearly closed and the IAC is closed, then it has to be a vacuum leak. Have you verified that the IAC pintle is actually moving? The IAC counts is only what the ECM is telling it to do, not if its actually sealing off the air bypass.

since you have messed with the IAC. The first thing that needs to be done is the steps to reset iac idle and throttle blade angle. alos since you have been messing with it have you reset to ecm? so it can relearn the idle points?

 

[bison]

since you have messed with the IAC. The first thing that needs to be done is the steps to reset iac idle and throttle blade angle. alos since you have been messing with it have you reset to ecm? so it can relearn the idle points?

Follow the procedures for setting the resetting the IAC (minimum air rate). I think they are listed on gnttype.org somewhere. If anyone has this link post it please. Usually around 20-50 counts at aidle when hot. It should not be at zero. This means the throttle blade is open to much.

 

[olds443]

I pulled and cleaned the egr. I pushed in on the pintle and plugged my thumb over the vac port and it held pressure without dropping at all. It should be good right?

 

[suicide six]

Break out the wd-40 and start spraying vac lines while listening for rpm change.Check for leaks from MAF to TB.If nothing is found,reset IAC,Idle screw and recheckTPS.

 

[suicide six]

IAC (Idle Air Control) Adjustment

The IAC function maintains idle quality through commands from the ECM, but, has NO impact beyond the idle range. Idle speed is set by the chip, not by the IAC adjustment screw. Looking at the inside of the throttle body, there are two holes in the lower portion fore and aft of the throttle blade. At idle, the blade is essentially closed and air enters the front hole, goes past the IAC plunger, and exits behind the throttle blade into the plenum. The IAC plunger is pulsed by the ECM to maintain a steady idle with varying engine load.

When the IAC is adjusted, we seem to typically look for IAC counts on our scantool somewhere between 15-25 when the car is in Park, the engine fully warmed up, and the A/C is off. The lower the IAC number, the less control the ECM has over the idle as the throttle blade begins to be opened. This setting may not be as critical as we often make it. You may find your car idles just as well at 40 counts as it does at 15.

With car in Park, engine fully warm, A/C off, look at the IAC counts on the scantool. If you wish to lower the count number, turn the adjustment screw clockwise. To increase the counts, turn it counterclockwise. Turn the screw a small increment, turn the engine off, and restart. This insures that the IAC resets and confirms the adjusted number. Continue until the desired number is achieved. Often, on stock set ups, about 1-1 1/2 threads of the adjustment screw will emerge thru on the lever side of the throttle body. Restarting also rezeros the tps as stated in the prior section and removes any effect on idle speed that may have occurred due to tps movement. The IAC counts will probably be 30 counts, or more, higher on a cold engine than on a warmed up engine. The counts will also be much higher in gear as compared to Park, and, higher with the AC turned on.

Remember that the IAC adjustment will change the TPS and that if the TPS moves past 0.46 volts, the idle may increase in speed as the ecm no longer thinks the car is in idle range. Therefore, if you are going to decrease IAC counts very much, it is a good idea to first lower the TPS down to 0.38 volts or so in order to prevent it from rising out of the idle range as you adjust the IAC.

It is not a bad idea to clean the throttle body out periodically with carb cleaner to keep the passages clean and to insure that the IAC function works correctly. Remove the IAC from the housing and clean any carbon or gum off the tip of the plunger and clean the seat as well. Don't power up the IAC when the unit is not installed. Otherwise, you may find the plunger is pushed out of the sensor. When reinstalling, very little torque is required. Just tighten enough to compress the gasket to prevent an air leak. Over tightening may crack the plastic interior of the IAC.

 

[WHEEZER]

I pulled and cleaned the egr. I pushed in on the pintle and plugged my thumb over the vac port and it held pressure without dropping at all. It should be good right?

EGR sounds okay then. Did you get the IAC fixed? TPS should be set next.

 

[suicide six]

EGR has no effect on idle,comes into play during cruise but a vac leak is another thing.

 

[olds443]

Thanks everyone.
I did spray the carb cleaner all around the intake and throttle body as well as the injectors and vacuum lines with no effect on idle or running at all.
Then I removed the IAC and replaced it with one I pulled from an 86 fwd Cutlass with 3.8. Immediately the idle improved.
Reset Computer, reset TPS and took for a drive.

Here are my scanmaster #'s now in park;

AF 05
LB 33
Bat 12.6
Int 128
Bl 157
ATS 121
Rpm 800-825
TPS .42
Iac 26
Clt 163
Think I will order a new IAC. Can't believe this one failed so soon, I think I bought it around June.
Now to find the cause for the high blm...... crossover maybe?

 

[Ormand]

Did you do the "pre-installation" adjustment on the IAC? It's possible that the pintle was not set right, so that it would not close all the way. The shop manual explains where to measure, and how to adjust.

 

[olds443]

Did you do the "pre-installation" adjustment on the IAC?

Uhh...... what? Do you mean the Buick Manual way, if so yes I tried that. It looks like the pintle is actually stuck too far out.