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Username Post: 4. Erratic Idle, stall 1989 4.3 S-10
matt49
Member
Posts 66
07-29-18 01:43 PM - Post#2741421    

The vehicle: 4.3L 1989 S-10

The symptoms: Erratic idle (fast), then stall, re-start by flooring it , idle sag while nursing it home.

The trouble codes: None. Had just re-connected the battery, so I probably lost all stored codes?

Any ideas would be appreciated!

Matt ('49 Chevy, 89 S-10, etc.)

gchemist
Senior Chevytalk Moderator
Posts 24955
gchemist
07-29-18 06:28 PM - Post#2741445    

Since it does run, we can assume the ignition systems is working, at least for now. So fuel supply is left. Can you check fuel pressure?
An adaptor is needed to check TBI fuel pressure. Shade tree mechanics can check another way. With a cold engine, pour a little fuel down the throttle body. Crank it. If it runs for a few seconds normally, you can assume fuel delivery is a problem. Likely the fuel pressure pump is not working properly. It will not give codes for low fuel pressure.
'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles

matt49
Member
Posts 66
07-29-18 07:54 PM - Post#2741451    

I replaced the IAC with a spare. Vehicle starts right up but initial fast idle was REALLY fast. A couple restarts have lowered idle speed somewhat. It's as though it's going through a re-learn phase.
I think I'm getting gas; it's just that the idle speed (and air?) has been all over the charts.
Thanks for your suggestion!
Matt

Mad Professor
Contributor
Posts 104
04-21-19 07:24 PM - Post#2764786    

Mine was doing that and I needed to replace some of the sensors (while back can't remember), I'll check my used parts box. I also cleaned out the throtle body and the EGR valve.

Also make sure you don't have a vacuum leak.
62 Willys wagon
67 CJ5 Buick V6 w/OD
68 Camaro RS/SS , 69 LT1 350, M22
73 C10 292 6, M21 muncie/hurst, 3:73 posi
89 S10 baja package






gchemist
Senior Chevytalk Moderator
Posts 24955
gchemist
04-22-19 07:36 AM - Post#2764813    

High idle at start or up and down idle, can be a vac leak. Spray some WD40 along the TBI base. If idle changes, the gasket is toast. Check hoses for cracks. The sensor on the passenger side is known for bad vac lines.
'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles

paulo57509
Senior Member
Posts 398
06-06-19 02:51 PM - Post#2767846    

My '92 Lumina does this anytime the battery is disconnected. IIRC, it has something to do with the IAC losing calibration from the ECM or some such.

It takes a Tech II scan tool to recalibrate the IAC idle learn.

An alternative to the Tech II is to start with a cold engine and set the parking brake HARD, start the engine and put the transmission in drive. Let the engine idle and allow it come up to operating temperature; I let the cooling fans cycle 2 or 3 times - it'll take a while. This should get the idle back to normal.
1987 IROC-Z 5.0L
1992 Lumina Euro 3.1L
2003 GMC Safari

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