1G 1G NA Starts, goes to 3,5k rpm then surges at 1,5k

[antanasdsm]

There was a problem before when at idle it suddenly dropped rpm and went back up so I messed with the ISC, I think, and now when I start it goes to 3,5k rpm and goes down to 1,5 and surges.

When I unplug the wires that go to the air filter (MAF?) it idles rough but at 1k-900 rpm. It would be nice if someone knew maybe whats causing this. At first glance it doesn’t seem that it has a vacuum leak.

It ran fine before with the drop of RPMs as stated before. It's a 1993 non turbo

 

[dwb]

The ISC is ECU-controlled and adjusts the idle based on how much air the MAS/MAF sees. That's why your idle changed when you unplugged it. The BISS (Base Idle Set Screw) is how you adjust the idle. Sometimes those can disappear, get out of adjustment, or the o-ring can go bad. Check that first.

I know you said it doesn't seem like a vacuum leak, but I'm skeptical. Are any vacuum lines unhooked or rotten? That's the next thing I'd check.

Are you seeing a check engine light? Have you verified the idle switch is plugged in and has a ground?

 

[pauleyman]

There was a problem before when at idle it suddenly dropped rpm and went back up so I messed with the ISC, I think, and now when I start it goes to 3,5k rpm and goes down to 1,5 and surges.

When I unplug the wires that go to the air filter (MAF?) it idles rough but at 1k-900 rpm. It would be nice if someone knew maybe whats causing this. At first glance it doesn’t seem that it has a vacuum leak.

It ran fine before with the drop of RPMs as stated before. It's a 1993 non turbo

you're going to have to provide more information. Please fill out a vehicle profile.
Has anything been done to the car lately?
Did it just start this or did you buy it that way?
It is not possible for the car to idle above 1500rpm unless the throttle isn't really closed (misadjusted cable, stuck plate etc) or the idle position switch isn't working.
I would start with vfaq.com and look at the idle faq section to get a basic understanding of how the idle circuit works.
You can't "mess with" the isc so what did you do? ISC is not adjustable, it's a computer controlled stepper motor.
Give us some details so we can help you.

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