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here's the deal: my car idles a little lower than spec, let's say 500 rpms, 700 in park (it's an automatic). the car shakes at this setting. when trying to adjust the idle screw, the iac kicks the rpms down to 600 unless i open it all the way up. at this setting the car idles at 1000 (smooth idle) but at almost 1500 in park . This would be fine, but the air leak created by opening up the idle screw seems to really affect mpg. the car has yet to stall, but if my subwoofer hits a powerful note, it comes a little close. i've ruled out the iac, but not sure where to look next. also recently changed plugs & wires, cap, pcv valve & also cleaned out the tb and air filter few months ago. also, car seems to run fine in all other aspects...any ideas?

Are you entering diagnostic mode when you adjust the IAC screw?

i usually just adjust it with the car running ???

There's a specific procedure for adjusting idle. If you don't follow this procedure, the ecu will make corrections to return idle to how it was before adjustment.

Tropical Emerald 1993 wrote:As for diagnostic mode.... it doesn't work. When you take out the wire it goes back to previous setting so you should adjust in in the standard way.

I think there's quite a few people on here who would disagree with that statement. It has always worked for me.

I agree, you have to do it in diag mode.

sorry for not replying, not getting emails regarding my "subscribed posts." i did run it through diagnostic. found a little more success in doing the breather mod to replace the vent hose that runs from valve cover to intake. seems to be idling in spec with idle screw closed. i'll give an update tomorrow.

about diag mode. any sure way to know if you're in it? ran the ten to the leftmost gnd and seemed as though car was more sensitive to electric loads ie headlights, but wasnt 100% sure if i was in it

On my car, when I'm in diagnostic mode, the engine will idle noticeably higher.

There's also a debate about when to pull the jumper wire. I pull it before turning off the car, others pull it after turning off the car.

I've never had problems doing it the first way.

my cat was the culprit. went high-flow and all is good. idles like a brand new car