I think he switched baback the OEM one, iiII

 

Okay so today I started by making changing in the IAC counts at idle in the tune. Result was no change in the idle. So I decided to take the IAC valve out and compare it to the original one that was replaced. At a glance both IAC valves look alike, but with a closer look the pintel heads were different. So i put the original IAC valve back in.
So then I started and ran engine until it reached operating temperature. Check and set throttle position sensor (TPS) to .54 (+/- .08) volts at idle. Ground terminals "A" and "B" on the ALDL, turned ignition key to fully extend the IAC pintel. Without turning ignition key off, remove connector from IAC motor
Turn key off and disconnect ALDL jumper.Adjust idle speed to 550 (+/- 25) rpm in park.
Turn ignition key off reconnect IAC motor check the TPS setting and reset the ECM. Depress accelerator pedal slightly then start and run engine for 5 seconds. Drive vehicle to assist in ECM reprogramming.
I haven't driven the car yet, but I got the idle down to 850 in park and 700 in gear. Hopefully I have it all ironed out. tomorrow will tell when I o for a test drive.
C409, Aklim, Kevova Thanks for the help guys!

 

I'm confused. Are you saying that you are now tuning the car? I thought you got a "Guess a Tune"? Why would you change the IAC counts in the tune? I would check the command or desired idle speed and see what it is before trying to change the counts.

Question is whether it will seal when closed or not, I would think.

How did you determine the idle speed? I have used a timing light with a tach built in or a scanner. The tach isn't as accurate as it could be.

Is this with the new system or the OEM?

 

Did your cam and other mods exceed what the 'self learn' can cope with in the first place? Most aftermarket systems at least give access to the gain factors for the PID loop to control idle and some give you a throttle follower that will program starting positions vs. TPS.

 

This is the 12267165 factory ecm out of an 87 vette. I'm not tuning the car and yes the car is running on a mail order tune. I have a Moates APU1 (emulator) which I've uploaded the mail tune into so I can make changes if needed. I adjusted the IAC count to see if the engine would respond and it did not.
I could see what the desired idle speed was in the tune, but the car was running well above it. At a cold start(open loop) the idle was set at 1100 rpm and then gradually drops as the engine temps rises. This was not happening.

 

..... If the IAC counts are @ 160 the ECM is trying to drive the idle speed higher ... ORRR ... the IAC is wired backward and its just doing as commanded ... that's why I suggested that you check the pinouts @ the ECM and at the connector for the IAC ... I don't know what differences there might be in pinouts of the '87 vs '85 ECM's but I would suspect that there are some ... Is your ECM receiving info from the coolant temp sensor ? ..... FYI , a wide open IAC should flow around 8gps air to the engine .....

 

What is the chance of a broken wire causing this issue? Say the ECM wants 30 counts, doesn't see it and keeps increasing the demand till it hits the limit

 

..... He is reading the counts from somewhere ... the ECM ? ... a broken wire should cause a not working at all scenario ... or works in one direction only along with a check engine light ... my original suggestion was to ohm check from the IAC connector to the ECM just to verify continuity and then to ensure that the correct wires were in all the right places .....
..... assuming the IAC wiring is all good , then the challenge is to find out why the ECM wants such a high idle speed ... the ecm also uses ignition timing to control idle speed .....

 

The self learning ecm (F.A.S.T. EZ EFI 2.0)I had in my car would not operate properly. That system was a MAP system that needed at least 12-13inches of vacuum to operate and my engine was making 10-11inches. A better cam (XFI cam)would have worked much better.

The IAC wiring is good I'm getting the correct voltage. I'm able to see the IAC counts because I have a Moates APU1 installed in the factory ECM. The APU1 hardware and TunerPro RT software allows me to see data in real time.
I had to take a step back againand go over all I've done to fix the problem to go see what I'm over looking.
I've replaced all the vacuum lines. I've tested the intake for leaks. I've twice replaced the IAC valve. I replaced the IAC housing gasket, I've replaced the throttle body gasket. I've plugged the vacuum port on the throttle body.
Then it hit me with a slapp in the face Check the top of the Throttle body. I have a BBK 58mm TB. On top of the TB is a cover plate with 6 Allen head bolt. So I get a Allen wrench to check the bolts and to my surprise they were loose. I proceeded to take the bolts out to look under the plate and there it was the vacuum leak. A metered hole about 8 or 10mm big. I made sure the gasket to the plate was in good shape, and bolted the plate back in place.
It's really late so I'll start the car in the morning to see how it goes. I don't want to wake the wife and grandson.
I'm pretty confident this is the source of my problem.

 

..... If your issue was a vacuum leak , the IAC counts would be zero ... Is your Engine Coolant Temp sender OK ? .....

 

..... My Holley self learning ECM is working fine with 5-6" vacuum at idle ... cam duration of 261/266 @ .050 and 227cc intake ports ... Idle tuning was a challenge because of the extra overlap air and reversion ... my junk idles at 84kpa on the MAP scale ... But I can manually adjust/select the Target Air Fuel Ratios (VERY important) and set parameters for self learn activation ... currently , my learn does not start until 2000 rpm ... Can you put a laptop on the FAST ? or are you stuck with using a touch screen ? .....

 

MY FAST ECM does not the option to connect a laptop. I removed it and went back to running the factory ECM

I check the engine temp sensor and it's work.
I started the car this morning and drove over to a good friend's house whom is a very good mechanic . We went over everything that could cause the high idle. A vacuum leak was ruled out. The high idle was being commanded. The TPS sensor was set to .54 volts which is the factory setting. So he suggested we lower the TPS. We lowered the TPS to .49 and that lowered the idle. Took it out for a test drive and it drove great.

 

How did you check the temp sensor?

That is really weird. Lets see what happens in a couple of days.

 

To check the temp sensor I disconnected the pigtail at the sensor and the reading on my laptop went from 177* to -39*. I use Tunerpro RT to monitor my engine data in real time.
Yeah it is weird considering prior to all this happening I never had this problem and the TPS sensor always ran at .54 volts.
Over the next few days I'm going to drive it as much as possible to see what happens. Hopefully the ECM improve as it learns.