Engine Fades Then Surges

[XanderWiFi]

This is kind of a two part question. The background: 3400 with CAI, Pacesetter headers, 2.5 inch pipes, high flow cat, magnaflow resonator/muffler.

It only will fade and surge at very random times such as when I pull into a driveway, stop (it fades a bit) and then surges back. The idle and driving is great-smooth acceleration, no surging, RPMs at warm idle stay at 750 or so. Just makes we wonder if the airflow is such that the computer cannot adjust quickly enough to the random stop?

Which leads to the other question. If our computers will adjust the airflow ratio appropriately, is there even a point to tuning until you get a turbo, etc. (the crazy stuff)?

Would a tune secure the appropriate mix so things like this wouldn't happen?

[Nate's Alero]

Sounds like your IAT is wearing, when you stop/start or go slow the throttle is closed, but you're moving and the Transmission is downshifting, the IAT needs to open/close to maintain proper idle for movement (~1200RPM) Clean the IAT and see if that helps. Mine does it too, not too often, so i don't usually worry.

[Redog]

I've been having that problem too. It's getting more often though.

My IAT is orginal

[mastershake]

Mine does that too, like it will surge when im pulling to a stop or Ito my driveway. You guys mean IAC not IAT right?

[mmorello82]

Mine Does it too. IAT is intake air temp sensor right? I'll give it a shot.

[XanderWiFi]

Yeah, I need someone to spell out the appropriate acronym for me as well.

With the pacesetter headers you have to relocate the O2 sensor farther down the pipe. Is that the culprit in the matter? Different sensor altogether if I am reading correctly (And I hope so as well.)

Seems simple enough though. Sensors are typically easy fixes. Nice to see I am not alone in this nor is it uncommon.

[sleepyalero]

mine also does it rarely, i dont worry much.

[a.graham52]

IAT: intake air temp [sensor]. IAC: idle air control [valve]. IAT will effect your fuel mixture while IAC will control your idle.

[03glgold]

mine does it every now and then...it does it more when its warm and/or is pushed hard right before stopping than when not.

[Nate's Alero]

Originally Posted by Redog

I've been having that problem too. It's getting more often though.

My IAT is orginal

Originally Posted by mastershake

Mine does that too, like it will surge when im pulling to a stop or Ito my driveway. You guys mean IAC not IAT right?

Originally Posted by mmorello82

Mine Does it too. IAT is intake air temp sensor right? I'll give it a shot.

Your IAT would cause hard shifting and an SES light if it was bad, Clean the Idle Air Control Valve first.

Originally Posted by XanderWiFi

Yeah, I need someone to spell out the appropriate acronym for me as well.

With the pacesetter headers you have to relocate the O2 sensor farther down the pipe. Is that the culprit in the matter? Different sensor altogether if I am reading correctly (And I hope so as well.)

Seems simple enough though. Sensors are typically easy fixes. Nice to see I am not alone in this nor is it uncommon.

Nah, That would just throw a P0420 code, Not make it run funny.

Originally Posted by 03glgold

mine does it every now and then...it does it more when its warm and/or is pushed hard right before stopping than when not.

That's the slow worm gear servo drive in the sensor SLOWLY adjusting. They need to have that drive to be strong, mine does it too, it never bothered me because the car never died.

[a.graham52]

Originally Posted by XanderWiFi

Yeah, I need someone to spell out the appropriate acronym for me as well.

With the pacesetter headers you have to relocate the O2 sensor farther down the pipe. Is that the culprit in the matter? Different sensor altogether if I am reading correctly (And I hope so as well.)

Seems simple enough though. Sensors are typically easy fixes. Nice to see I am not alone in this nor is it uncommon.

Originally Posted by Nate's Alero

Nah, That would just throw a P0420 code, Not make it run funny.

depends on what o2 sensor is moved. if its O2S1 then it could effect how the engine is running if the ecm cant compinsate for the better air flow in which case you probably would get a "lean" code such as P0171 or any o2 sensor related code (voltage stuck high/low etc). p0420 is cataylest efficency low code and only sets when the cat is no longer working as it should (worn out/broken up) and is triggered by the post cat o2 sensor "O2S2" which is set behind the cat... pretty much the only function of that o2 sensor. i do not belive xanders concern would be caused by the pacesetters as it happens in a lot of these cars stock. i agree that its probably a slow IAC vavle and agree to try and clean it first. otherwise i think there pretty cheap.

[XanderWiFi]

I have no SES lights or check engine lights. No randomly and none permanently. Sounds more like a prelude to one though.

So clean up the IAC valve is sounds? Anyone post a how to for this? Not familiar with it.

I am assuming it is the O2S1 sensor (pre-cat) because well, it was moved from the top of the headers to where they all mold into one pipe before hitting the cat. I have not touched any sensors below the catalytic converter.

[xXManwhoreXx]

Put it in neutral and rev to like 1000 slowly and let off. If it stutters its IAT

[XanderWiFi]

I'll give it a shot

[xXManwhoreXx]

Mine sounds cammed at idle when its warm, my rpms go up to 400 than back to 1000 if i tap it once lol

[XanderWiFi]

neutral or park? I had it in park. Mine idles naturally at 750. Revved it to 100-1500 but it never faded below 750 when releasing. The drop back to 750 would hang at 100-1200 for a microsecond or two though.

How do you clean this IAC valve?

[sleepyalero]

if it were me, i would remove the whole throttle body, take out sensor, clean sensor with electric cleaner and use throttle body cleaner on the TB and where the sensor goes it, but let dry before you put back together.

[a.graham52]

Sounds like a good way to clean it. But price one out. May be worth putting a new one in if cleaning the old one helps. Also maybe clean Ur mass air flow sensor a bit and see how that goes.

[XanderWiFi]

so clean the MAF sensor and hose the TB with TB cleaner. I'll give it a shot. But a couple years since I cleaned the MAF sensor, but did not find much on it then when I did it.

[a.graham52]

Don't clean the maf with tb cleaner! Stuffs too rugged. They make actual maf cleaner u can use.