novaks47

I've got a '96 with the LT1. I've got a rough/erratic idle, and have narrowed it down to the IAC. I took off the throttle body, took it apart, cleaned everything, replaced the gaskets, and put it back on the car. And yes, I cleaned out the IAC passage and the IAC. The car has 90K miles on it, and the IAC is done for. The passage way was beyond filthy, as was the pintle. No doubt it was sticking. Anyways, looking at the various brands, the price difference is huge! I see Airtex/Wells for around $16, and the Delphi and ACDelco's are around $60-80. Any experiences with the different brands? Recommendations?

aklim

Get the Duralast one from Autozone and see how it works out. If something goes wrong, they can warranty it out and put it towards another one, be it Delco or whatever you want.

novaks47

Thanks, I had forgotten all about the Duralast stuff. Checked out their site, and the $100 one is made by Wells. The $80 one is made by Walker, no idea if there's any relation to the exhaust company. At least they say who makes the parts now! Used to be you had to open up the box and look, haha!

aklim

Regardless of what factory it come from, most important is what spec it is made to.

MatthewMiller

The only thing the IAC controls is idle speed - not mixture or spark. If you have an erratic idle speed, that could be a failing IAC. However, if the idle is actually rough or erratic in quality (as opposed to just speed), then the IAC won't cause that. Are your idle problems also happening at cold start, before the car goes into closed-loop mode? Is your car idling higher at cold start?

novaks47

Oh, so maybe it's not the IAC then. It doesn't do it when I first start the car, when it's holding a higher RPM. The car starts easily too. Shortly after the idle drops, it'll start to act up. It's more frequent once the car is good and warmed up. Other than that, it runs great. No hesitation off the line, pulls hard throughout the rev range. I did replace all the spark plugs too, as they were in bad shape. Plug wires are in very good shape too, no corrosion on the contacts, and the outer insulation is still soft and pliable. I replaced the EGR valve as well, just for good measure, as they're pretty cheap and easy to replace.

MatthewMiller

I would say that if the car reliably holds a higher idle when cold-started (like it's supposed to), then the IAC is probably doing its job. Just to make sure, are you getting a check-engine light, and/or do you have any trouble codes stored? I'd be looking for a sensor that is only used once the car enters closed-loop operation (basically, after the car warms up). I'm thinking it's not an O2 sensor, just because I'd expect it to run worse than you're describing and it would probably throw a CEL/code on a 96. That said, if the car has the original O2 sensors, and especially if it has lots of miles, it might be good to change both pre-cat O2 sensors anyway. They aren't expensive, although I understand that on a stock exhaust system they can be a pain to swap out. Another consideration might be a vacuum leak somewhere that's small enough to only affect idle once it gets down to its lower warmed-up rpm. Make sure your MAF sensor is clean (only use appropriate cleaner for it though), too.

novaks47

No trouble codes stored, pending or present. Checked that before I got the car, and again a few times after, just in case the dealer or previous owner cleared them out. I'll clean the MAF next, that's easy enough. I suppose that could be it, as the air filter when I got the car looked like it could've been the original the car was built with, it was so dirty! Intake tract looked clean though. I had thought about the O2 sensors, but dismissed them as the car has 90K, so seems a bit early for them to quit. Who knows, maybe one of them is slowly dying. All the vacuum likes look ok, sure there's a few on the way out, but no visible holes. I'll have to spray them with something while the car is running to be sure.

aklim

Check out what you get for IAC counts on a scanner

aklim

This isn't the 60s anymore. You really should buy an OBD2 scanner and it can be used on other cars. Codes don't mean that much other than the sensor is out of the set parameters. You need to see what the sensors are saying and match them against known values that someone might have gotten for that vehicle.