IAC Valve issue - Help

[RiggsLW81]

had the IAC valve replaced in my 02 caddy seville sts, as the original one was shot. since putting in the new one, first few days was fine, ran great... now I am getting random surges in RPMs when im idle at a stoplight and the car is in gear. up to 1000-1200, then back down to 500, and repeats, and repeats.

if i put in in park, the RPMs surge up to to 1500-2500 and stay there, as if im holding the throttle down. both these problems come and go, and do not take place every day, but at random times. IAC was then replaced a second time under warranty, in case the part itself was bad, (problems still persist after 2nd install)

it also occasionally stalls out, but seems to happen only under 5 mph, like in heavy stop n go traffic, or ina parallel parking situation.

all these problems are totally sporadic, and do not happen all the time, but very randomly.

I did my homework and checked caddy forums, it mentioned to make sure the throttle body was cleaned as well (and it was during the IAC install), some sights spoke of a "learn procedure" for the IAC, which I performed as well. they did not work. I even took to my local caddy dealership to ask tech what they thought, and they guy said the part is plug and play and doesnt have a "learn procedure". wanted me to drop off the car, but no way in hell I'm taking to to the dealership who wants $140 an hour in labor !!! yeah right !!

any ideas here guys? im at a loss and need to get this sorted out as it is my daily driver. thanks

[Stevoone]

Why did you replace the IAC (what do you mean by shot?)? Any codes in the computer?

I've replaced a lot of intake plenums. It's not the intake itself but the rubber extension that goes from the manifold to the water pump housing/ throttle body. They get a small crack in the bottom that you won't be able to see. When the crack develops they tend set lean codes p0171 and p0174 and they can also cause the idle to fluctuate, surge and stall.

[RiggsLW81]

replaced the IAC because the symptoms pointed to a faulty IAC, (surging randomly, high /low rpms randomly) and then the car finally wouldnt stay on after starting, rpms dropped low, and the car stalled. put new IAC in, worked fine a few days, now problems are back, replaced twice.

however, they are aftermarket IAC's (not ac delco) - thought maybe try with an ac delco as ive heard some parts must be OEM to coinside/function properly on some cars (but i cant be sure to say its not an old wives tale either...) any truth to this?

[MyFirstZ]

I'm with stevoone on this, if you can try smoke testing the intake, reading your post sounds like an air leak.

[Stevoone]

This is the piece I mentioned. http://www.rockauto.com/catalog/more...042&cc=1379932

You need to pull the intake manifold to replace it, not too difficult.

[RiggsLW81]

thanks for your input, I will try this test this week and see what's found. just curious...is there any truth to my question regarding some cars not "taking to" aftermarket parts, (ie, needing an oem ac delco brand IAC) to function properly?

[RiggsLW81]

checked the rubber coupling via reccommended test, there are no cracks in it. its in solid shape. so back to the drawing board. curious if anyone would chime in on the oem/ac delco vs aftermarket question I mentioned earlier. any validity to this?

[MyFirstZ]

a lot of components aren't made by the manufacture but from other companies so an aftermarket sometime will be identical just reboxed.

Did you have faults or just that higher revving and surging ?

I still recommend smoke testing the intake for air leaks.

[Stevoone]

What brand IAC did you use? ACDelco, Standard and Airtex Wells are the brands I usually use. Ive had just as many defective ACDelco parts as any other after market brand.

Two defective parts in a row is a little unlikely but I've had it happen before.

Did you smoke the intake or did you spray around with carb cleaner? When the rubber extension cracks it can be difficult to locate it with carb cleaner. If there is any doubt about that piece it is best to just replace it. I replace it any time i need to move an intake or water pump housing, thats just how common they are.

As far as other vacuum leaks. The three most common that i see next to the rubber plenum are the Intake Gaskets, EGR tubes, Secondary AIR components (diaphragms, vacuum lines). And also specific to the Seville the Intake resonator, I've had a lot of them installed wrong.

Do you have a scan tool? Any codes? Any codes before you put the IAC in?

[The_Bishop]

A scan tool will definitely help troubleshoot this. If the IAC counts are zeroed out and the timing is doing the lambada in sync with the idle fluctuations then you definitely have a vacuum leak.

[RiggsLW81]

about a month ago, had the IAC replaced a third time, this time a genuine AC Delco part, and abracadabra, solved ALL the issues. idles where it should, no high rpms in park, no more surging, etc.

I had my doubts it would fix the issue, but it did. been running flawlessly for a month now since putting the AC Delco IAC in. I guess its true that some cars are more troublesome and require genuine brand parts, lesson learned, and am quite happy the caddy is running smoothly now. thanks to all for their help

[sweetbmxrider]

Or the aftermarket is making crap replacements

[WildBillyT]

Glad to hear it's all cleared up!