That's normal behavior after a battery disconnect.

The computer has to relearn parameters to control the IAC.

I always turn/adjust the manual screw that your not supposed to touch.

It acts the same as the idle speed adjustment screw on a carburetor.

I set it so the idle can not go below my desired Engine idle spreed.

Thanks
Randy

 

I think I'd have to disagree about the battery disconnect, and messing with the adjustment screw. I've never had that issue with any S10.

 

The onboard computers do lose their knowledge of optimal settings when the battery is disconnected. In that case the computers default to a standard setting, but that standard setting should be reasonable and not cause those problems.

If it runs just fine after 6-8 times restarting, then it might be a temperature issue....runs ok when warm, but lousy when cold. Do a few tests to see. Drive it around and let it warm up and then turn it off and let it sit a few minutes. Then try to start it again while still warm. Does it start ok? Or does it revert back to the 6-8 times restarting to get to normal?

 

I know it's not a 4.3L but when I started up my truck with a completely different engine in it, the battery had been disconnected for a couple weeks, and it started right up and idled right at 850rpm like it's supposed to.

 

Yes, this is how I expect it to behave. It also makes a difference how long it is disconnected. A few minutes is no problem but overnight screws it up.

After power disconnect, the ECM will default to factory until it can relearn, but the default should have you idling high, not low. You have an issue that is hidden by your ECM, while not bad enough to set a light on its own, it will slowly get worse till it does. More than likely you have a vacumn leak somewhere.

Thanks, that makes sense. I'll look for a vacuum leak.

That's normal behavior after a battery disconnect.
The computer has to relearn parameters to control the IAC.
I always turn/adjust the manual screw that your not supposed to touch.
It acts the same as the idle speed adjustment screw on a carburetor.
I set it so the idle can not go below my desired Engine idle spreed.

The Gen 2 Blazer I towed for a while never did this so I can't believe it is truly normal. If I can't find a vacuum leak or some other underlying problem turning the idle screw might be a workable solution.

 

After power disconnect, the ECM will default to factory until it can relearn, but the default should have you idling high, not low. You have an issue that is hidden by your ECM, while not bad enough to set a light on its own, it will slowly get worse till it does. More than likely you have a vacumn leak somewhere.

 

An S10 with a possible vacuum leak? - whoever has heard of such a thing - it can't be! 😁😁 Really, it's definitely something to check out.

 

I have this new-to-me ZR2 that I'm prepping to tow behind my motorhome. I've installed a battery disconnect so it can be towed with the steering unlocked and not drain the battery. Anyhow, after disconnecting and reconnecting the battery it idles very slow ~400 rpm and dies when it's put into gear. Keeping my foot on the throttle helps but it doesn't really recover until it's been restarted at least 6-8 times. Then suddenly it idles and runs just fine. There is no SES light and no codes saved.

Obviously the idle air control is misbehaving, but why? Can anybody give some insight into what's going on?

This sound like loose connections , when I ran my pcikup with loose connects it wanted to die and the rpms would drop I would double check all connections and make sure that are tight and connect together good.

 

What king of loose connections? It runs great all the time except for right after the battery has been disconnected for several hours.

 

I'd like to know more about flat towing. I too have a 2002 ZR2 and a Motorhome, but unlike the 95 Jeep I use to own with a 2WD, 4WD HI, Neutral, 4WD LO, the ZR2 lacks the Neural. I 've been under the impression not to flat tow the ZR2.

 

The owners manual says not to tow, flat or otherwise. I'm sure some people will chime in with their stories of doing it with no issues. I think GM probably knows better.

 

A 9 volt battery in the cigar lighter to retain ECU memory when the battery needs to be disconnected might help. Your issue is definately not normal. Check the base settings of the IAC and the throtte. Maybe the previous owner was tweaking it to compensate for some reason. The ECU will retract the IAC to base setting after battery disconnect long enough for he capacitors to discharge. Each start it will push it out a little farther than the last. Might just be a worn out IAC. I used to see it on the computer command control carburators after someone else "fixed it".

 

And it could just be that with 185K miles the ECU is compensating for an aging engine.

I looked high and low for a vacuum leak and didn't find any issues. I did do the bandaid fix of turning the set-screw at the idle stop 1/4 turn. Now when it's misbehaving it will idle at 550 in neutral which is enough to stop it from stalling.

I don't think a 9v battery would last long enough to prevent the problem. With the key in the "off" position (not "lock") several of the dash lights stay on and who knows what other systems are powered. Probably everything except for ignition and fuel. The whole point of disconnecting the battery is to prevent it from being drained while I'm towing. I can't tow with the key in the "lock" position. I have considered taking the steering lock out of the column. Then I could turn the key to lock and remove it and still be able to tow. Just haven't decided to go that far yet.

 

Any codes stored? A jumper in the DCL and count flashes. I would check the the TPS. If it is set wrong or jumpy it might take a few restart for the ECM to relearn. I think thats a OBDI so you need to use a multimeter and metal paperclips to back probe. Analog ohmmeter here would show smoothness better than the digital sampling speed of the DVOM but either works. Also check the IAC smoothness of movement with jumper wire to battery. On the CCC carb it was actually an idle control motor. Different but the same. Set the throttle opening and IAC according to service manual and then look for the real cause given the problem happens mostly when the ECM is reset. I think you have to jumper two terminals in the DCL but it's been a while so check the manual. As I remember it is almost counterintuative. Fuel pressure or Egr sticking another possiblilty but unlikely from the symptoms.

 

A 2002 model is OBDII. I have a reader but have not seen any stored codes.
I haven't hunted down a service manual yet. Any suggestions where to look for a PDF or at least a good price?