F-body-fan

Hi Guys! Been I while since I have been on the site, & I wanted to re-visit a problem I have with my 1987 Iroc 5.7. The car is all original with 60K on it. I have owned the car since it was 4 years old. I don't drive it much at all, in fact it sadely sits in storage sometimes as much as 3 years without being driven.

Anyway, the car runs & drives very well, but the problem I am having is upon a cold startup (50-70 degrees outside) is idles very rough for about 10+ seconds. If I start it without touching the gas pedal, it will just barely stay running & sometimes will stahl out. If I play with the throttle for the 10 seconds or so, it will smoothen right out.

the weird thing is, on the times that it is stumbling it will hit a point after 10 seconds or so, where its almost like a switch is flipped & it idles up & smoothens right out. It will then run perfectly like it always did years back.

So my thinking is that there is something that changes in setting from initial cold start up?

What I have checked is the fuel pressure & TPS voltages. TPS is at .52 (I think that is close?) fuel pressure is good & consistant.

Thanks for your thoughts & ideas

F-body-fan

I did the paper clip trick to completely close the Idle air control. Then with the IAC disconnected I found my idle was set so low It would not stay running. Turned the idle scew up until it was at steady at 450 rpm's. reconnected the iac & found my TPS was now reading 61 volts. I adjusted it back down to 52V & will have to wait until tomorrw to see if that makes any difference. Thinking not, but who knows. the idle adjustment was off a little anyway.

F-body-fan

I realize I have turned this thread into more of a diary, but thought I would add a few things. Today, I pulled the throttle body & cleaned it out. Replaced the IAC valve & re-adjusted the idle setting with the IAC & also the TPS. It seems to idle a bit smoother, but the same problem exists. Dang...

Here's a small video of a cold start up. When you see the RPM's at 500, its barely hanging on, once it pops up to 1000 & stays there, it will be fine all day. I know this is not a big deal, but its driving me nuts now that I am trying to solve it......

(Added 09/19/2011) I forgot to mention that in this video, I don't touch the throttle ever. It initially jumps to the desired idle, then struggles to stay running, then jumps back up to 1000 rpms. In fact at one point its so rough it bounces my camera around. Once its warm, this never happens again on start ups.

http://automationsystems.ws/images/5.7stumble.wmv

Sorry if this should have been in the TPI section,

8T9Formula

iTrader: (1)

Check your injector coil resistance...The factory minimum spec is 10 ohms but good ones are generally in the 16-16.5 ohm neighborhood. Low coil resistance means the amperage (current) draw through the injector driver (a fancy term for a transistor switch inside the ECM) that triggers the injectors will be too high and it will shut down or only work intermittantly.

F-body-fan

Thanks 8T9, I checked them, they are all over 16 ohms 16.2-16.5. When you watch the video, this only happens when its cold, or sitting for 6+ hours. Once its been running it will start & run pefect. It can sit for 1-2 hours & will start & run smooth. There must be a function that is specific to cold start ups? Its done this I'll bet for the past 10 years. But seeing its sits most of the time, I figured I would get to it. Now that I am "getting to it" its proving to be a little more difficult.

I would add, that once this hickup is over on cold start, the car really runs fantastic. Idles smooth & runs strong. I do have a Snap on Solus, so I can read all info that is available through the ECM, but I am not seeing anything that is obvious.