Random idle surge

[Nudnik]

After the autoX event on Saturday. I drove home & had a random idle surge up to 2k rpm twice while at a stop light. I left LSP, drove to Hurst to pickup a part from a fellow Miata fan & then started driving home. I drove at hwy speeds w/no problems & when I came to a stop light in Lewisville, I noticed that my engine revved up to 2k rpm, held there for a second or two & then dropped back down to normal. About 15 seconds later it did it again briefly & then never happened the rest of the drive home. Prior to that I noticed the engine dropped down to 600+/- rpm when I put it in neutral & then rebounded to 900+/- (a/c was on). It's almost like the throttle position sensor is getting spastic but thought I would ask around before I go swapping parts.

Any thoughts?

[POS Racing]

What year is the car? I'm thinking IAC Valve.

[POS Racing]

IAC Stuff - http://www.miata.net/garage/isc.html

[Nudnik]

What year is the car? I'm thinking IAC Valve.

It's a 1990, stock 1.6L

[POS Racing]

It's a 1990, stock 1.6L

Yep still thinking IAC valve.

IAC Stuff - http://www.miata.net/garage/isc.html

[Nudnik]

Yep still thinking IAC valve.

IAC Stuff - http://www.miata.net/garage/isc.html

Thanks. I've started reading this info. I'm a little confused but I'm sure it'll start to make sense the 3rd or 4th time thru.

[POS Racing]

Thanks. I've started reading this info. I'm a little confused but I'm sure it'll start to make sense the 3rd or 4th time thru.

Short version - Crud in IAC valve try cleaning valve.

[Rogue]

Run a bottle of Techron Concentrate thru it before you buy a $400 part.