jump up a bit when you put the tranny in park from drive? IE, with a fully warmed up engine, you pull up to your favorite parking spot at WallyWorld, stopping with foot on brake, then just goto park. The idle races up quickly to 1500+, then slowly drops down to normal within about 10-15 seconds. I know some other folks have seen this before. I set the idle speed adder in P/N to 0rpm, but 50rpm with AC on.

It gets kind of annoying when you pull up somewhere and park, and have listen to that idle race up for a few seconds, then calm down.
I looked at some paramters with my scan tool, but nothing really jumps out at me. Thought maybe my scan tool was forcing a high idle, but it does it with the tool disconnected as well.

Is this just a normal situation for our cars?

TIA, Mike

 

Hmmm, I must be doing something wrong,
I dont have a favorite parking space at WallyWorld.

You need to hunt up RBobs paper on IAC stuff, poking around the DIY-EFI GMECM FTPs should get you what you want.

If you set your decoder ring to the 42 mark and look at the bin I posted a couple weeks ago you can read thru the IAC changes I made on that bin.

Personnally I keep the IAC as inactive as possible, ie the max value on the GN is 38, and stock was like 150 ish.

When you start doing chips, you can play all kinds of games with them

 

Thanks Grumpy. Just checked out your 42 bin, and read some of the related posts. Looks like your Park Steps vs Coolant has been tweeked a bit. Kind of resembles the ARAP settings. I am using my stock '88 $32B values, which has the IAC parking at 80 steps when warm. So looks like some changes are in order.

Still have to look at the info on the DIY-EFI boards.

Anyone else have comments?

PS Been burning chips for over a year now. FWIW

 

Mine does exactly the same thing. I haven't been able to correlate the IAC counts to anything specific in the eprom tables. In the "IAC Warm Park vs. Temp table, the values for everything above 80 degrees C is at '5', yet my IAC is at around 55 counts when in PARK.
My Carbon Canister has vac to it at all times though, I did find if I plug the hose at idle in Park, it does come down to about 850 or so and IAC stays the same. Guess I'll wire in the purge canister solenoid.
*
Is the table mentioned above the same table you did some "tweaking" on, if so, what values did you change them to?
Thanks

 

Yep, you got the correct table. I had my stock '88 values in that table, now I run the ARAP numbers. It has the steps going from 125,100,75,50,25,10,5,5,5. These values seem to help the situation. Just haven't gone any further with it.

But I did read up on this IAC stuff in my shop manual. Seems that the idle is SUPPOSED to jump up, after you shut down the motor, then restart. There is a test called out to check this. Read up on what Grumpy said, and check out his table. He has the IAC steps at 5 from 37C on up.

From what I understand, this table tells where to park the IAC moter when engine is off at XX coolant temp.

I would get that vaccuum issue fixed first.

 

have you tried adjusting the iac ?????? jump the feild service pins on the aldl and turn the kep to run (engine off) keep ingntion for 30secs. before turnning ignition off unplug Iac and then turn key off. disconnect the battery to clear all learned blm's and iac steps. plug iac back in with battery disconnected. reconnect battery. start car imeadiatly put in gear and hold in park for 30-45 secs to help it relearn the iac steps place in neutral for 30-45 secs. this cures most bizaire idle jumping and such is see in gm cars. its the gm adjusting proccedure. good luck i hope this helps.if not clean the iac passage and the seleniod tip and try again.

 

I have recently just set my min idle speed. That procdure is very similar to what you describe. It was at 400, so I bumped it up to 450, then readjusted the TPS for .54v. Also had my TB cleaned up real good this past winter. I think I may just need to make some more changes in the table. Grumpy suggests keeping the IAC from moving as little as possible.

 

Bruce also says to do what feels best for your motor. I have been playing around with the IAC settings based on Bob Rauscher's excellent article and a review of Bruce's final answer bin. My motor doesn't like a total of IAC steps down in the 38 range. It seems to work better up around 70-80 which is still quite a bit lower than the 145 in the stock bin. But you'll never know unless you try it.