IAC (Idle Air Control)

[87K54WD]

Not a question for the K5. This is in regards to a post I made in the "other rides" forum titled "Hesitation." Seems like I saw someone say something about IACs last week or so. Could this unit contribute to hesitation to about 30 mph? Car runs great after about 30 mph. Highway performance is excellent. Were these IACs known for going bad on GM cars in the late 80's? Are these units strictly for idle (not touching the throttle), so the car doesn't die. Sometimes the car dies after coming to a stop in reverse. All the symptoms I am having are in that post noted above. Thanks in advance for ANY input on what could be causing this. I am tired of taking it to the dealership every year and half to have them "re-learn the IAC counts" ... whatever that means.

 

[Fierospeeder]

its just for the idle.

I might want to see if the ign module is bad, or your torque lockup which is on the trans, if you have a front wheel drive.

Im positive you dont have a fuel problem if your car does fine after 30mph. Another thing that can kill the car is a stuck EGR valve, which can stall you at stop lights. Also are your plug wires new?

74 VW Beetle
84 Pontiac Fiero
87 Ford Thunderbird Turbo
83 Honda Nighthawk 550

 

[grtwhite]

Sounds like an EGR valve problem. Had the same thing happen to me. Rough idle & stalling in reverse & even in drive at a stoplight. Hope this helps.

- Jay

 

[CaptCrunch]

What kinda vehicle and which engine we talking about here?

-Mikey
1987 Chevy K5 Blazer- 350 TBI
<a target="_blank" href=http://coloradok5.com/gallery/captcrunch>http://coloradok5.com/gallery/captcrunch</a>

 

[87K54WD]

It's an 1988 Oldsmobile Cutlass Supreme V6 (2.8L) Multi-Port FI. The original post was in the "other rides" forum under title "Hesitation." That post has all the details. I looked at my invoice receipts of repairs at the dealership. Everytime this happens, they say, "IAC out of range, clean bore, relearn idle." EGR and IAC both were replaced at around 40,000 ... car now has about 95,000 miles. So what do you all think? IAC or EGR? Also, would the parts from Autozone made by Wells be just as good as AC Delco?

 

[Fierospeeder]

When your driving 40 and let the pedal go, does it stall? If it doesn't then its not your IAC.

The way to the iac is "relearned" is just driving faster then 30mph and the computer sets it up for you. Thats when you replace it.

Go to your EGR valve and play with it. Grab a screwdriver, but use your finger if you can fit it in the diaprham. Push the diagram towards the top. The car will start to hesitate and stall. This is normal. Pull out the vacuum line, and push the diaphram and see if you can get it to sit at the bottom. Try driving the car without the vacuum line and tell us what happens

With the screw driver, make sure you dont poke a hole in the diaphram, some are fragile.

74 VW Beetle
84 Pontiac Fiero
87 Ford Thunderbird Turbo
83 Honda Nighthawk 550

 

[CaptCrunch]

Sounds like all the dealer is doing is pulling the stuff off the car and spraying it out w. cleaner and making sure they aren't sticking. The idle relearn on the old style 3.1's and 2.8's can be done by disconnecting the battery for about a half an hour and then start it up and block the wheels... let it sit idling in drive (wheels cocked and p-brake on MAKING SURE it isn't going to go anywhere)...forget how long you do it for... but something like 10 to 15 minutes.

I would start to lean on it being some where else. Obviously check out the basics... ignition system... fuel filter, etc. Maybe invest some time and a few bucks to pull the top plenem off so you can check the injectors w/ a multimeter. GM injectors are known for being PIA's and going out. If nothing turns up from that point it would be time to look into the MAF, Fuel pump, FP regulator... I would put money on the MAF or the fuel system from the sound of it but can't say for sure without driving it. Another thought... dealers are great for newer cars... like stuff made in the last 5yrs w/ a tricky problem... but unless it is a whacked problem on a newer car you are just throwing your money away IMO. Ask around for a local shop w/ a good certified Master tech and known history for solving drivability problems. A shop like this is almost always full... In the long run you will save money by getting a cheaper labor rate and they can look up all the TSB's on a quality program like AllData or Mitchell.

-Mikey
1987 Chevy K5 Blazer- 350 TBI
<a target="_blank" href=http://coloradok5.com/gallery/captcrunch>http://coloradok5.com/gallery/captcrunch</a>

 

[**DONOTDELETE**]

Look at the TCC lockup solenoid on the trans. When you drive down the highway you should be able to feel the torque convertor free up when you touch the brake pedal, and then feel it lock up when you push down on the throttle. I had to change the TCC solenoid on my mom's car because it would stall everytime I would pull up to a stop sign.

Later,
Doug

4 wheelin's not a job, it's an adventure!