So I bought a sc1 a few weeks ago , I have replaced several things due to its 24 y/o. I did a valve cover gasket, oil change, oil filter , motor mount, trans temp sensor, iac, cleaned throttle body, ran Seafoam, new belt, and charged Freon. Well after replacing the iac the car started to bog while I was driving losing power and when I would put it in park the rpms ran 2k, well I had a mechanic check it out 2 diff mechanics actually , and they both told me 2 diff things. 1 said it was the iac again; the other says vacuum leak. Well after the first mechanic checked it he sprayed some cleaner around the engine and power steering pump, and it resolved itself for awhile. Now it is idling high again and won’t let me get power again,as well as random misfires. It also struggles more if I have my charger plugged in or my air running. I ran a diagnostic last night & my rich to lean threshold failed and my long fuel trim 3 was -56.7 which I know is super off. I had a code of p0410 secondary air system. But I am tired of paying money to someone who doesn’t fix it , and misdiagnoses. So I’m looking here to hopefully have someone who can steer me in the right direction.

 

From what you've described it sounds like there are multiple issues occurring simultaneously. It's hard to say exactly what the problem is without testing. However, your mechanics did perform some testing already, and from what you've shared I'd say I am very confident that you do have a vacuum leak somewhere, probably from the vacuum hoses near the Throttle body, or the PCV hose, or the intake manifold gasket itself (common problem for some Saturns, especially near cylinder 1).

To help find where the vacuum leak is, you can try spraying carb cleaner (or brake cleaner or starting fluid) in short bursts near suspected vacuum leak locations helps find a vacuum leak because it temporarily seals or enters the leak, which affects the air/fuel mixture and causes the engine RPM to change.

With the engine idling, spray around suspect areas (like vacuum hoses, intake manifold gasket, throttle body, etc.)

If there's a vacuum leak, the carb cleaner gets sucked into the intake through the leak.

This adds extra fuel, causing the RPM to surge or stumble briefly.

That change helps you locate exactly where the leak is.

It is also possible that your new IAC is not functioning correctly. One thing you can do is force the IAC to go through its relearn process. This is done by disconnecting the negative terminal of your battery for 10-15 minutes, then let the car warm up completely at idle (do not press gas pedal at all), to full operating temperature, and then go for a drive. be sure to come to a complete stop at least a few times on your drive. This will allow your to relearn idle parameters.


It does sound like there might be some other things potentially going on, but its probably best to start with the most obvious thing and fix that first, which seems to be a significant vacuum leak.

 

Do you have access to a scanner that can read live data? Another thing you can do is use a scanner to look at what your MAP (manifold absolute pressure) sensor is showing. The MAP sensor is responsible for adjusting fuel injection, ignition timing, and idle control. A bad MAP sensor, or a MAP sensor that doesn't have proper access to the system vacuum, can cause idling, acceleration, and fuel trim issues.

Might be something to look at after you try finding the vacuum leak (especially if you can't find one).

 

Idle relearn on an S car?

Indeed the third generation sohc's suffered from a Mal installed intake manifold gasket compliments of a Goofy robot. When it happened it seemed to primarily be around cylinder one at the intake. Make sure when you spray around the intake runners that you spray underneath the runners as well, or shall I say the underside where it meets the head.

Put the old IAC back in and see if the idle comes down. Actually, was the high idle ever an issue with the original IAC?

Whack fuel trim like that really sounds like a massive vacuum leak or a disconnected hose.