I'm not sure if this belongs here or in the TPI forum, but I'll post it here.

When I start my car in the morning, it will idle rough at about 900 rpms, with the IAC maxed at 160, when I have it set to idle at 1100 rpms. I'm watching it on the Diacom. However, as soon as it goes into closed loop two minutes later (heated O2 sensor) the IAC drops to about 150, and the RPMs go up to 1100 and it idles smooth just fine. So why does it have a hard time idling at 1100 in open loop? Thanks...


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1991 Camaro Z28
5.7L 5-Speed (originally 305)
317 RWHP, 418 RWTQ
13.23 @ 107.62 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Member: SoCal F-Bodies
-=ICON Motorsports=-

 

I'm curious why it needs 150 IAC counts to idle in closed loop. Seems like there is a fuel or timing issue.

For example, if you have your timing retarded you need more throttle opening to idle a given speed.

 

Have you looked at your IAC Step Counts Vs Coolant Temp settings?

 

One thing that will tremendously help keep your IAC motor from maxing out is setting your warmed-up at idle IAC counts to 10-15. Mine used to max out too, and the IAC counts only went down to 80 or so. Once I brought them down, I never maxed out the IAC in a cold start-up.

I also saw the same thing happen with my 305, which was an internally stock engine, but had headers and other mods on it. I think you're running either too rich or too lean in open loop, which is why this is happening. You could probably set the O2 timers to go into closed loop a lot lower with the heated O2 sensor, like 10, 20, and 30 seconds. I think Mike Davis has his even lower, as his will go into closed loop w/in several seconds of start-up.

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Greg Westphal
'87 IROC 355TPI/A4

 

Kev C'Mon now.

Reset the IAC to drop the IAC counts down to around 10-20 at idle when the car is warm. Resetting the appropriate tables that Glenn mentioned will also help ... but just resetting the IAC will cause the most noticeable improvement. As you know - there is no way that your IAC should be at 150-160 counts at idle. That means that the IAC is compensating WAY too much.

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

The Idle Steps vs Coolant Temp table is stock for an AXXD chip, I havent messed with it because I didnt understand it. If the car needs a certain IAC value to idle at a certain RPM, if you change that value then how does it adjust the idle? I mean, if the car needs an IAC value of 50 to idle at 800 RPMs, if I tell it in the chip to set the IAC to 25, then it wont idle at 800 RPMs, will it??

I am fighting a lean idle condition that started when I put in the 24lbs injectors over the 22lbs. The injector constant is 23.9 lbs, fuel pressure is 48 psi. The BLM's are in the 138-148 range. Adjusting the VE tables does very little. Maybe I have a vacuum leak or a bad injector?

Last time I tried to adjust the throttle to get the IAC counts down, it went all to heck. The car idled really rough and stumbled, the vacuum went from 17" to 12", and the KPA was really high. I set it back and everything was fine again. I'm hesitant to touch the idle adjustment again.

 

If they are true 24# injectors and not SVO injectors, then I'd adjust the injector constant down to fix the BLMs first, unless they're just lean at idle, then it's a VE table thing. If they're SVO injectors, then it sounds like more of a mechanical problem like you mentioned. Did you re-adjust the TPS after adjusting the IAC counts? I'm surprised the idle got worse.

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Greg Westphal
'87 IROC 355TPI/A4

 

They are LT1 24# injectors, not SVO's.

The BLM's are over 140 up to about 2000 RPMs, then they smooth out to around 128. However I have previously tried upping the VE tables, the injector pulse width was up at 3.5 ms at idle, and the BLM was still over 140. I really think its something physical now.

I just did the IAC reset procedure. I put the paperclip in the ALDL, waited 30 seconds, then disconnected the IAC. I found the throttle blades were all the way shut. I opened them up quite a ways, then started the car and adjusted the idle for about 750-800 rpms according to my diacom. However, this raised the KPA from 42 to 58, the injectors went from 2.0 ms to 2.4 ms, and the BLM went from 141 to 149. The car idled like crap. I plugged the IAC back in, and there was no change in it. It was at 92 before, it dropped to about 83. I wasnt gonna drive it like that, so I set the throttle blades back to all the way closed, and the KPA came back to 42, and the IAC is at 91 and the car idles much nicer. What gives?? The IAC vs Coolant Temp is stock, I havent touched it. It shows 10 steps at 80 degrees C. If its showing 10 how come I'm getting 90? Also, my chip shows the timing to be 24 degrees at idle, plus the 6 initial to make 30. Diacom is showing I'm getting 22-23 degrees total timing. This is crazy!

Thanks for your suggestions guys.

 

Gotta get more fuel in there.

I believe the 730 uses timing for idle speed control in addition to the IAC. My WAG is that with the blades closed and the IAC open so far the ECM is adding timing to keep rpms up. This causes the Kpa to fall. Usually more timing at idle raises vacuum (to a point).

I think the steps in "IAC steps versus coolant temp" are where the IAC will run on a bone stock engine in perfect tune. The ECM puts the IAC where ever is required to hit target idle speed. This way vacuum leaks and other failures don't change idle speed.

That sounds right. The initial is subtracted from the spark table then added back by the dizzy's physical position.

Have you changed timing while its idling? Move the dizzy acouple degrees retarded and advanced to see how it reacts.

[This message has been edited by Brent (edited August 30, 2001).]

 

What kind of Cam do you have? I have the LPE219/219 and it idles at about 50-55kpa. The bigger the cam the higher the kpa at idle(ask Tim and his big *** cam). If I remember you have the Hot cam? If so your kpa should be higher at idle(around that 50kpa mark?).


Brendan

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1987 IROC-Z L98,SR,EB 6085's,LPE 219/219 SR Cam, Crane 1.6RR, EB TPI Base, 58mm TB, Stock T5, 30lb SVO, AFPR, K&N, EB TES, Catco Cat, 3" Borla Cat-Back, Accel cap,rotor,distro/other crap, Aluminum DS, 94 Disk Rear, Adjustable Prop Valve, Precision 3.73 Gears, Weld in Sub-Frame Connectors, Hotchkis LCA's, KYB Shocks/Struts, Poly Bushings all over the place, Moog Upper/Lower Ball joints and Tie Rods ends/Idler Arm, Big stereo, 730SD Conversion.

To see the ROC, Check out the webpage Here

 

My 218/224 cam idled at approximately 55kPa. The HOT cams that I have seen idle anywhere from 50-60 with the average being about 55 (which is in tune with what I was getting with my 218 Xtreme. I now idle at approx. 72kPa - roflmfao.

Anyhow - the observation that the car idled like crap after you adjusted the IAC doesn't mean that much. You need to set the idle and then retune the car for idle because you have now upset the balance that you previously tuned for. The only way that things are going to work out for you is if you get your IAC counts down (car warm).

Tim

------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

If I can make it idle at 41-44 KPa and have 17" of vacuum, why would I want to mess with that and have less vacuum? Vacuum is good!

Can I lower the IAC vs Coolant Steps table? Will that affect the IAC? When I reset the idle as above the IAC stayed in the 90 range so I dont see why retuning it would make a difference... Am I just being stubborn and missing something here?

I should try connecting my passenger side O2 sensor and see if anything changes. (I have two O2 sensors, but only one is connected at a time) I might have a leaky or sticking injector or exhaust leak on one side that is affecting the O2's and BLM.

 

Nature hates vacuum.

I can make an engine do alot of things, but the point is getting things the way the engine wants. That's the whole trick.

If your throttle blade is closed all the way then you do have a problem, since at that point the idle is under 100% of the IAC.

Check for a vac leak, you might have to play games with PVC, brake booster line restrictions to drop the air leakage past the butterflies to a reasonable amount. THEN try backing up your idle timing, and playing with your mixture.

 

I just made an observation on your signature. You have a manual in a place where a manual wasn't offered. Did you start out with a manual bin for a 305? If you did, disregard the post but if not this may be part of your problem.

 

hectorsn, my manual trans belongs there, as its been with the car since it left the Van Nuys plant in 1990. But the 305 engine has been removed and replaced with a 350. Thats what (originally 305) means in my signature.

Yes I started with a 305 5-speed BIN and modified the cylinder size and injector constant for a 350 with 24lb injectors.

I'll mess with the car some more tomorrow and report back my findings...