Runs rough. Giant sucking sound from intake.

[dsrt]

Sounds great right?

I 88gt with 3800 ser II sc swap. It has developed a few issues seemingly over night.

The car starts and then switches to a giant sucking sound from the intake and will continue to run like crap until it finally idles so low and choppy it dies.

I can restart it and rev it a few times to make it go away and then it will run fine. After its warmed up it wont do it. Cars been running well for 5 years since the swap. No internal or external work has been done to it lately. Fuel pressure looks good. Any ideas?

[ericjon262]

Welcome to the board.

what ECU are you using? stock 3800 SC ECU? is it throwing any codes?

[Jalisurr]

Sucking noise to me means air is being forced through a restriction somewhere in the intake system. I'm not super familiar with the plumbing on a 3800sc, but I had a somewhat similar issue on a C4 corvette when one of the intake hoses got old, it would start collapsing under throttle, make a sucking noise, and run poorly.

If it only happens on startup and you can get rid of it by revving it...maybe some sort of air valve is getting stuck?

[dsrt]

Its the pcm out of the Buick PA Ultra. Its been tuned through sinister performance like 10 years ago and has been fine all this time.

No codes are being thrown.


Theres no intake tube. I just have a air filter mounted to the throttle body. Been that way for 10 years or so as well.

[The Dark Side of Will]

IACs are generally pretty reliable, but they do fail every so often.

Also on the 3800SC there's the blower bypass valve that is operated by the PCM via vacuum solenoid. That can change intake airflow.

Do you have any way to read PCM data? E.g. an OBDLink reading and the Torque app on your phone?

You can watch IAC counts and see what the PCM is asking the IAC to do.

Can also be CTS or IAT temp sensor failure, as that could cause it to be rich enough to stall out when cold.

[dsrt]

I dont have anything to read data other than a cheapo HF scan tool. I'd prolly not know what i was looking at if I had it. Willing to learn but don't really know what i need to get to get started with. Is there a specific OBD link I should look at getting?


Although i will say. If I start it cold and starts doing this i can give the IAC a sharp RAP with a screwdriver handle it stops. And wont to it again until it's cold.

Iv'e at least ordered another IAC to be here shortly.

[The Dark Side of Will]

Is there a specific OBD link I should look at getting?


Although i will say. If I start it cold and starts doing this i can give the IAC a sharp RAP with a screwdriver handle it stops. And wont to it again until it's cold.

Iv'e at least ordered another IAC to be here shortly.

I've used both OBDLink MX and Blue Driver. Blue Driver has more capability, but is more expensive. A lot of Blue Driver's capabilities relate to other systems on a car, so buying it for just a Fiero might not be good value, BUT it will help out immensely with any modern car you have.

If tapping the IAC as it begins to show the symptoms makes the symptoms go away, it sure sounds like your IAC is getting sticky.