High RPM's on start up

[joshwilson3]

Doesn't surprise me. I found diiferent procedures when investigating this as well. When I documented all of the steps provided earlier for throttle body adjustements, I stayed as true as possible to the GM FSM instructions. Specific to IAC reset, no changes required.
Depress accelerator pedal slightly
Start and run engine for 5 seconds
Turn ignition key off for 10 seconds
When you depress the pedal sligthly, the engine draws in extra air, more than what is required by the ECM to reach targeted (programmed) RPM setting. So the ECM extends the IAC pintle, trying to reduce IAC air flow. Since air flow across the plates is more than the ECM can manage, the ECM signals the IAC into full extension (closure). The ECM and IAC are now insync with each other. On restart, The ECM uses several variables and prom settings to signal initial IAC position. Post procedure a scanner should be used to verify the IAC counts.

Ok, thanks. I'll stick to the FSM method.

 

[MBDiagMan]

Have you checked to see if there are any codes set? Even if there is no check engine light, there might be codes in memory. You don't need a scanner for this, just a paper clip.

 

[joshwilson3]

Have you checked to see if there are any codes set? Even if there is no check engine light, there might be codes in memory. You don't need a scanner for this, just a paper clip.

No, there haven't been any codes. But I've disconnected the battery a few times as well. This weekend I'll probably try a new IAC and see what that does. If it fixes it fine. If not, then I'll just keep looking for a scanner and go from there. I noticed today on a hot start up while still in P, the idle was hunting after it fell back down from the 1700 rpm flare up. I gave it some throttle for a bit, and it settled down to a steady idle before I put it in gear. But it probably doesn't matter as you don't leave it in P for long on a start up. Once in gear, no problems.

 

[boomdriver]

These IAC motors are pretty well self setting as far as the operation goes. The only thing thats required as far as maint, is making sure its not too long when first inserted. After that, the ECM will move it until the desired result is obtained. Anywhere over idle the IAC does nothing. TPS signal is then dominate. Thats why TPS min settings are important to a decent tune up. If thats off, there is no reference for other mngt systems.

 

[joshwilson3]

New IAC didn't change anything. So, I guess I'll pull it and put the old IAC back in and keep an eye out for a scanner.

 

[TedC]

New IAC didn't change anything. So, I guess I'll pull it and put the old IAC back in and keep an eye out for a scanner.

ECM resets IAC to closed position when engine is turned off. This is reference zero. At start up, a given number of counts are issued to open IAC, and normal control will begin. So we need to know what signal the ECM is sending out to control the IAC. If the signal is to close the IAC and the RPMs remain high, then it would point to a non ECM related issue like a vacuum leak. If the signal is to open up the IAC, and keep it open, and the RPMs remain high, then we have some type of electrical/electronic issue (bad ground, connection, ecm or prom). Scanner data will tell you the desired RPMs (targeted RPM) and actual RPMs, and you can monitor how the ECM reacts to make actual = desired. The top 5 reasons in the FSM for incorrect idle speed; vacuum leaks, throttle cable sticking/binding, ECM ground, IAC system, and park/neutral circuit.

 

[joshwilson3]

ECM resets IAC to closed position when engine is turned off. This is reference zero. At start up, a given number of counts are issued to open IAC, and normal control will begin. So we need to know what signal the ECM is sending out to control the IAC. If the signal is to close the IAC and the RPMs remain high, then it would point to a non ECM related issue like a vacuum leak. If the signal is to open up the IAC, and keep it open, and the RPMs remain high, then we have some type of electrical/electronic issue (bad ground, connection, ecm or prom). Scanner data will tell you the desired RPMs (targeted RPM) and actual RPMs, and you can monitor how the ECM reacts to make actual = desired. The top 5 reasons in the FSM for incorrect idle speed; vacuum leaks, throttle cable sticking/binding, ECM ground, IAC system, and park/neutral circuit.

I'm keeping an eye out for a scanner. I'll probably go Autoxray since they are more common than others, and you can still update it and have tech support.

I'll probably look at the 3000, 5000, or 6000. But the 3000 would probably be cheaper to get than the others. I had called the Autoxray tech support about the 3000. And the tech guy was trying to tell me I'd really need to upgrade the 3000 to a 6000 or something. Haha. OBD I is 15 years old. I don't really think an upgrade is gonna give me more data than what the 3000 will provide. So I won't bother with a $200 upgrade when I could probably just buy a used 6000 for less than that.

 

[TedC]

Watch out which manufacture and model you buy. I saw a recent post here on CAC that some models that support both OBD-I and II do not work on L98s. No issue with the AutoXray 3000. I'm using the latest firmware.

 

[joshwilson3]

Watch out which manufacture and model you buy. I saw a recent post here on CAC that some models that support both OBD-I and II do not work on L98s. No issue with the AutoXray 3000. I'm using the latest firmware.

Thanks. Do you have that PC 500 so you can upload the readings to your computer? That looks like a good thing, but is an extra $50.

Autoxray PC 500:

www.autoxray.com/product_detail.php?pid=76

 

[vetteboy86]

Do you have a laptop? Have you considered scanning software like Datamaster. TunerPro also has scanning software. The only other thing you need is an ALDL cable.

 

[joshwilson3]

Do you have a laptop? Have you considered scanning software like Datamaster. TunerPro also has scanning software. The only other thing you need is an ALDL cable.

No I don't have a laptop. But I had looked at getting an older laptop with XP. That would probably be a few hundred.

What is the best/cheapest scanning software to get? And can you recommend a place to get an ALDL cable?

 

[vetteboy86]

If you can get an inexpensive laptop, getting software and the cable, in my opinion is affordable. I am using Data master for logging ECM information and use Tuner Pro for tuning. I have considered trying Tuner Pro for logging as well, just have not gotten around to it yet.

I thought they had them over at moates, but I was unable to find any. Probably should keep searching. A google search turned up several. I can't remember where I purchased mine. They have ALDL to USB now which is handy, earlier cables required a USB to serial converter.

 

[joshwilson3]

If you can get an inexpensive laptop, getting software and the cable, in my opinion is affordable. I am using Data master for logging ECM information and use Tuner Pro for tuning. I have considered trying Tuner Pro for logging as well, just have not gotten around to it yet.

I thought they had them over at moates, but I was unable to find any. Probably should keep searching. A google search turned up several. I can't remember where I purchased mine. They have ALDL to USB now which is handy, earlier cables required a USB to serial converter.

I looked up some of those cables and saw some were around $90. I figured that was alot for a cable and could probably get a better deal by looking.

One thing I read though on the $90 cable is it has a resistor you can turn on and off. And saw someone mention the cheaper cables has that resistor in place at all times. And that the resistor can cause the MAF to make the car idle high, so you'd want that certain resistor off. Do you know anything about that, or should any cable work?

Here's where I read that:

GM OBD-I ALDL Cable (USB) and Differences - Tuner Tools Forums

 

[vetteboy86]

I will need to do some digging to find your answer. Mine has a two position dip style switch, and I thought it had something to do with data transfer speed. Not for sure though.

Also, something nice about DataMaster, is you get 20 free scans.

 

[vetteboy86]

I'm pretty sure this is the place I purchased my cable.

AKM Electronics Home Page

 

[joshwilson3]

How do you get the scanning software to work? I've got a Moates cable and downloaded the driver. I've got 3 different scanning software downloaded: Winaldl, Tunerpro, and Tunerpro RT.

Hook everything up, programs open, start car. And nothing.

 

[vetteboy86]

Hmmm, unfamiliar with those used as scanning. I use Datamaster. I'm pretty sure vetteoz uses Tuner Pro.

 

[vetteboy86]

It looks like ALDL monitoring is only available with TunerPro RT.

 

[joshwilson3]

It looks like ALDL monitoring is only available with TunerPro RT.

Yeah, that is the way I read it. You have to use the TunerPro RT to read ALDL output.

I'll probably give Moates a call to see if he has an idea on what else to do. I followed the instructions in the Help section, but I had to stop as it told you to click on something under Tools I believe, but I didn't see the prompt it said to click on.

 

[TedC]

On my 1988 and 1989, you need a 10K resistor (pins 2 and 4) to flow ALDL data when using a home made serial cable. 3.9K enables factory test mode. 0K enables diagonostic mode (flash codes). Open mode did not work on ECM 1227165.