So here is my story about 10 months ago I rebuilt, upgraded and swapped in an L98 motor, rear, rebuilt the trans... pretty much redid the whole car. The original motor was just a tired out L03, the new motor is a L98 from a 87 Iroc but I run a 91 ecm and Map sensor. Evers since the install iv had this cold idle problem. It revs up and down, if i put it in gear snap the throttle and stop it will stall out, then give me somewhat of a hard restart, but the idle just keeps surging up and down for the first few mins, then it goes away and is fine, drives great the rest of the day or until I let it sit for 6 or so hours.

http://gardengrasp.com/firebird/transformation.htm

no vacuum leaks, new injectors, new cts. Its not the ecm because i just installed an EBL P4 flash (which is great by the way) and the problem never changed.

Using the search feature this seems to be a semi common problem and the threads seem to hit a dead end alot of people seem to not figure it out and just get used to letting it warm up for 5 mins before driving it. But its annoying and I wanna finally get to the bottom of it.

Here is a list of mods:

Rebuilt to stock L98 bottom end
Stock Heads - Valve Job, Cleaned, Decked, Valve Stem Seals, Manley springs & retainers
Crane 2032 cam
TPIS Big Mouth Intake Base
Ported SLP Runners
ported plenum
Hooker 2055 Y pipe and headers
Magnaflow 3" all the way back


here is a video i took of what it does



im open for suggestions

The WUD would provide a ton more data.

The IAC is maxed out at 145, may need to open the throttle blades some. Shoot for 20 - 25 steps on a warm engine in P/N.

The MAP is rather high for idling in P/N. On a cold engine the idle speed should also be higher. The max'd IAC is preventing a higher idle speed.

RBob.

i got the blades open to .74v on the scanner.

what would a high map indicate?

That the engine is having trouble running. If the AFR on the gauge is correct it is also running very rich. Which is unusual as lean usually causes an engine to surge.

RBob.

The map sensor measures change in intake manifold air pressure. The map is the exact opposite of manifold vacuum. The map reading is low when vacuum is high.

You might want to let the engine warm up and set the min idle speed with the iac commanded in and disconnected then check the iac count. After this I think I would try raising the target idle speed and adjust the lower ve in this rpm vs kpa range.

yeah im gonna be changing the throttle body in a few weeks because when i was changing the cts i relized the plenum was porte for a 52mm, then i stumbled upon someone selling one for a hundy so i picked it up. ill set the min idle speed at that time

It just got shipped from az lol

sure did, how did you know that?

I am working on his memcal and I got a few small parts from him. Inside tpi guy here

any progress pat ?

well as expected nothing to do with the O2. but we all knew that.

this weekend plan on swapping throttle body, changing the connector for the iac, reseting the min idle... how do i do that again? do i need to unplug the set timing connector?

doing all that assuming i can get to my shop, snow storm supposed to roll on thru fri and saturday

Turn the key on and jumper the aldl that will command in the iac. Unplug the the iac and start the car and set the min idle speed. I think the spec is 450-550. Do this while the engine is warm.

i can use the scanner to put it into field service mode as well? also do i disconect set timing connector?

you don't need to disconnect the est just put it in field service with the engine off and unplug the iac after that.

I agree with RBob, most cars I see with a cold surge is from being to lean but I have also seen cars surge cold when overly rich.

After you set the IAC, if it still surges when cold a quick test that I do is just pull off the brake booster hose to make a vaccum leak, this will lean out the AFR, if it gets worse you need more fuel, if it get better then lean it out some.

Also what does the narrow band read? and what is your startup SA table set at.

SA -Start Up
-40 / 14.06
-16 / 14.06
8 / 8.79
32 / 5.27
56 / 4.22
80 / 3.52
104 / 1.76
128 / 1.76
151 / 1.76


wideband hangs around 10.8 or so, definetly rich, add a little brake clean and it will stall it out

idle spark error tables, should be 2 of them. one for spark advance, the other for spark retard. add 3-4* timing to both tables, this gives the ECM better control over idle.

Not very familiar with EBL but I assume its an adder to the main SA table? and what is your main SA table sat at for idle? and does the EBL use a wideband only or does it use a narrow band also. I also noticed it was in open loop the hole time, you have it set that way?

its in open loop cause it was first cold start of the morning

For an 89, to reset IAC the Haynes sayes ... not sure if 91's diff ?

Depress gas pedal slightly, start engine and run for 5 seconds. Shut off.
Wait 10 seconds, then start car again ... let idle ... done.

This is also after you've reconnected battery/reset ecm

are those the tables you are talking about?

Right table add to the 40-60kpa, I think you said it was smelling real rich when it is surging if that's the case lower your ve a little in the same kpa area.

in the area i highlited? in that main SA table or the VE Table - Low Speed?

or is this the table?

I would leave the SA tables, to me they look fine, but take out some VE, try around 45-50 in the idle cell area.

sorry kinda new to tuning can you explain "take out some VE, try around 45-50 in the idle cell area."

See that VE table, these are the main fuel correction tables for SD setups.
The top numbers are kpa (vacuum), so when you first started your car it was at about 55-65 kpa (it was a little all over the place cause of the surge, it should be more steady) anyway to lean it out go to the cells in 50 to 60 (top)
and say 700 to 800 rpm (side) change the numbers in those cells to say about 50.

Also learn to use the WUD, much better then a snapon scaner, look at injector PW (pulse widths), this is how long the injector stays open.

Your settings of about 70VE seems much to me but then again my engine way cammed up, me ve at idle is like 30.

cool thanks for the explaination... like that?

yep those are the tables im talking about. those are also values set for a stock engine, since your engine is modified the ecm requires a bit more control. try adding 3-4* to both tables, all cells, and see if it slows down the rolling idle. i had to add 8-9* after the lopey cam install

BUT this is just a test to see if it gets better, one thing to remember is VE table needs to be smooth.

so add like 3.5* to each number in that column? do i do that with adjusting the ve low speed table?

so if that did make it better what would i do to make it smooth?

you could try 4*, and see if it helps which it should. once the idle is a little more stabil you will be able to start fine tuning the fueling

Well what I do when tuning a new setup I first get the Idle down, meaning idles perfect, then work on the VE tables, I do this by turning off AE,DE and PE, I then lock it in open loop, from there I match the VE tables to the wideband by matching the cammanded AFR, next I work on spark tables then AE and PE, when I'm done I start all over again to fine tune.

like that?

looks good, have you tried it yet?

no im gonna try it in this upcoming week. ill report back when i do. thanks for all your help guys, i really appreciate it. good night for now

Remember one of the major first timer rules of tuning is change one thing at a time if your not familiar with tuning, you may just make things worse, and always have bins saved before you change anything.

By the way what injectors are you using and what do you have set for the injector constant.

bosch 3 injectors - havent touched the injector constant from stock. is that a table?

This one:

INJ - Injector Flow Rate**

And this one for displacement:

INJ - Displacement of 1 Cylinder**

If this flag is set:

Option Word 2 - Bit 1 - IdlSa

Then the idle SA is from this parameter:

SA - Idle State SA

Which is further adjusted via the CTS & VAC table and the idle SA compensation tables.

If the idle state SA value is changed also change the main SA table is that area to match, then blend in to surrounding cells. This is to provide a smooth transition from idle SA to the main SA.

RBob.

when you say smoothing, would i be correct to assume you mean change the cells around the cells i just modified.. maybe 2 rows deep in all directions to smoothly transition to teh values of the rows liek 3 away in all directions?

More or less. Can also bring up the graph after the main SA change. This easily shows how to blend in the others as it is visual. Can grab a point or more and move them with the mouse.

RBob.

Well the ecu does math to calculate how much gas to inject into the engine, so lets say my stock bin has the injector constant set at 19 then it's doing the math for a 19lbs injector, so if I put 30lbs injectors on the engine that had 19 originally and not change the constant to 30, then injector PW math will be wrong.

i understand that but as long as i am sticking with the stock LB/hr like i did it should be ok to stick with factory aujp settings correct? they are bosch 3 but same as stock flow rate, i think it was 22/lbhr

I think gp90gta was referring to the constant witch you have set correctly and the injector offset will effect the amount of fuel the injector is spraying. You could double check the injector battery offset with south bay it may be a little off from the bosch 2's.

Wasn't the LO3 a 305? 305's came with 19lbs injectors, if you but in 22's then you need to start there. There is also battery and latency correction tables, you can do these later to fine tune but make sure that constant matches your injector size.