High idle and slow return

[thebrosh]

I recently bought my 1992 MX-3 GS 1.8L V6 all stock. When I turn the car on in most conditions when it hasn't been ran for hours it will idle quite high around 2K rpms. Even after the warmup period when the idle should return to 650-800 rpms it still stays quite high between 1,500 and 2,000 rpms. After a good solid hour of driving and I come to a stop the idle will slowly make it's way back down to almost normal 900 rpms. I checked the most visible vaccum hoses and couldn't detect any leaks. I noticed after about 25-30min of driving my engine light comes on but I do not notice a change in the car's driveability.

I am hoping someone has had the same problem and can describe their troubleshooting process.

Thanks.

-Michael

[Ryan]

My car revs like that, although I'm sure my problem is my IAC, Idle Air Control Valve.... and checking codes is easy, just search on this website. There is a search option in the red banner.

[Mad Cow]

Check your coolant level, my friend's mx3 had this problem. What happens is not enough coolant goes through the temp. sensor that controls cold idle speed and it doesn't heat up as much as it should.

[thebrosh]

Thanks for the tips. I will check the coolant and IAC valve. I believe those are the culprits. I brought my car in to the Mazda dealer to have the codes checked and they said it pointed to the oxygen sensors malfunctioning. So they tested the oxygen sensors and they are fine. The mechanic said that it may be because of Oregon's 10% ethanol mix in our gas that is causing the error codes. Does this sound plausible?

[fowljesse]

Yes. I got O2 codes once in a while, when returning to idle, after a freeway drive. I haven't gotten it since I only get Chevron gas.
Welcome to the forum. Where in OR are you? We've sort of got an MX-3 club going. I live just outside of Vancouver, and the others live all over the P-town suburbs. We get together on the weekends to get Mooneggs' car going There are other OR guys that come out once in a while. I expect about 8 people at our next meet.
Don't waste your $$ going to the dealer to get codes. It's easy.

[thebrosh]

I live and go to school at OSU in Corvallis and sometimes go out in Portland on my way to and from my parent's place in Hood River. So does Chevron gas not use any ethanol?

[fowljesse]

I believe they don't... Either way, I stopped getting codes when I switched from Costco gas. Let me know if you have a few minutes in the Stumptown.

[Newfie_dan]

I have this issue but I only noticed it when the temp dropped here, I will be checking the coolant level but I am more inclined to think its the iac, I pulled the codes with my obd2 scanner and never got any which I thought was odd. I think the iac may be sticking with the colder weather.