my IROC (350 TPI 5 speed) won't idle when it's cold. My current burn is just APYP with a couple constants changed. I thought I had an IAC problem, but I replaced it and went through the diagnosis to ensure that the wiring & ECM are playing nice.

I can't remember offhand what the IAC is doing when it's cold because I haven't fooled with it since last fall (just got the car out of storage) but if I recall correctly it started out pegged, and slowly worked its way to 0.

I have to hold the throttle at 1500 rpm when it's cold. Any drop below that and the car will stall. Once it warms up it idles nice right at 750.

The problem was worse with the ARAP bin, so going to one for a manual trans definately helped. But now I've got to get in there and play to get it better and I have no idea where to start. Any suggestions?

 

does it smell really gassy ?? if so your probobly running lean.

 

I'll pay closer attention next time I start it, but I don't recall having a gas smell, just your typical exhaust smell. With the car warmed up and idling well, my car doesn't show any signs of running lean. My block learn and integrator are right around 128, and my oxygen sensor cross counts seem to be pretty normal.

 

What are your IAC counts when fully warmed up?

Like Funstick said, it may be a lean issue, I'm assuming that this motor isn't stock. A wideband is worth its weight in gold, I can't tune without the silly thing anymore

 

funstick........... i am a little confused but why would a gassy smell indicate a lean condition? i was under the impression that if it smelled gassy it was a rich condition?????

 

I need to put the scan tool back on the car, but if I recall correctly, my IAC counts go to zero and stay there when the car warms up. I've gone through the IAC/TPS resetting procedure a dozen times. Unplugging the IAC seems to make no difference in the idle. I replaced it and had no change.

 

Assuming the IAC/TPS are adjusted correctly and working properly(which I'm sure they are if you've been over it a dozen times )

What are the specs on this engine? Access to a wideband would tell you if your running lean on warmup causing it to stall, may be a timing issue.

I recently got my 383 195AFR headed 219LPE cammed engine running and it would run very lean after the startup enrichment ran out(this is with the 730 not the 165 that you recently swapped to), it runs fine when completely warmed up also. I had to add some gas to the open loop enrichment tables.

The engine also liked around 32d of timing while warming up, and then gradually decays down.

 

Here's the info on my motor:

It's a 355 with flat top pistons, moly rings.
461 fuelie heads (read: Old school)
summit 214/224 .442/.465 112lsa cam
24lb/hr SVO injectors
SLP runners
accel base
52mm holley throttle body
heddman 1 5/8" headers
5 speed transmission

My motor obviously isn't stock, but it's not that wild either. I'm using a stock APYP bin except that I changed the injector constant to 25lb/hr and I fooled with fan temps.

I have a heated oxygen sensor but I haven't wired the heat element since I put the new harness & computer in. But, even if that helps, ultimately there's something making my IAC act stupid.

Rather than speculating until the end of time, I'm going to try and find time to get the scan tool on the car tonight so I can actually say what's going on for sure. Then we can hopefully figure out what my problem might be.

 

I would be tempted to find the "Open Loop % A/F Change vs. Coolant" table and start adding fuel at the problem temps like leirch said.

Regards,
Eric

 

The IAC has a commanded park position, that it closes and then opens to when you kill the engine.

When you first start the engine it goes to the start position, in some code it is the warm park position.

then as you first crank the key it gives the engine a huge shot of fuel. Within the last week or 2 I posted a data log of an engine start and the MAP cranking down for the first .5 sec of run time.

First is the IAC working, and is it's channel way clean?.
Then what is you min idle set like.

Then work out the start first run routines if it ain't right after all of the above.

Assuming the basic tune is right

 

Jim,

You might try two things. My IROCZ use to behave in a similar manner. I increased the idle RPM by 100 at the colder coolant temps, and I increased the amount of fuel for a cold start. These two changes helped alot. I am not in front of my PC at home right now so I can not give you the name of the two tables that I changed. BTW: my engine idles better using something other than an ARAP based Eprom.

 

Grumpy, the IAC is brand new, as is the throttle body. The IAC housing was cleaned thoroughly and is 100% clean. I ran the diagnostic procedure in the GM service manual to verify that the IAC wiring and computer is operating properly. I set my idle based on Vader's well known procedure.

I did notice the other day in the very brief period that my car was running right (until all of a sudden a severe lean condition developed ) that at idle with the car warm my IAC counts were at 26 right where they should be.

Doc, thanks for that info. If I ever figure out this sudden lean situation, I hope to be able to revisit the IAC issue in the future.

Ain't technology great?

 

Well, the lean condition is gone. Whether I fixed it or it just went away, I haven't figured out yet. Now she's a tad rich.

But anyway... with the car idling, my IAC counts are at zero. The car is idling at 900 rpm, and the desired idle is at 800 rpm. I still have to hold it at 1200-1500 until it warms up or it'll stall.

For reminders, it's an APYP bin that I changed a couple constants on. I haven't touched any of the tables.

Until I get this thing running a little more predictably, I wonder if I might be better off with a bin from a manual 86 vette? That may be a bit more tame and not so tempermental? What do you guys think?

 

Something that you may want to double check are your MAF connections. Make sure that there are absolutely no leaks in the air intake system between the MAF and the TB. Then no vacuum leaks after the TB.

Any leaks between the MAF and TB can drive one crazy as the MAF doesn't get to measure that air.

RBob.

 

Hmm, maybe a bad tank of gas?.
To come and go is odd.

Try running some fuel system cleaner thru it.

Only use the Berryman's or Quaker State stuff in the metal cans, the other stuff is just alky, the stuff in the cans has Tolulene and other things in it.

 

Jim, try giving it more timing in the timing vs. coolant table...at cold temps.