1990 vert, JDM S5 swap, all stock parts. Recently when I start up my car, the idle was a bit high (1500-2000rpm). But in the past couple of months it has gotten worse and worse. Now it idles at around 3k rpm. I need to trouble shoot this problem, but I'm not sure where to start. Can someone give me some pointers as to what I should look at. Would a vacuum leak cause this?

 

Damn, I guess I'm the first person to have this problem in an FC. I'll keep you posted as to what I find.

 

So if you rev it up does it go to 1.2k or so then back up to 3k?

I'm betting its a problem with your throttle body, something there isnt right

Also is it assisting the throttle, the little motor that steps it up to warm the engine? Mine used to work correctly now it can be 102F outside cali weather and it'll still stay at 2-3k rpm for along time.

 

I had a similar problem in the past. It was very annoying when my car would idle at 3k in traffic. My throttle cable was in poor condition. Some of the sheathing was ripped on it, which caused the cable to rust in a few spots.

I ordered a new throttle cable from Mazda and it fixed the problem.

You might want to check the cable itself too.

 

Thank you very much for the replies. The throttle cable is less than a year old. I had to get a new one when I swapped the TII engine in there. If I rev the engine, it drops down to maybe 2.5k, then back up to around 3k. I will be removing my intercooler, and double checking the all the attachments on the TB and the cable itself this weekend. I will keep you updated on anything I find.

 

Ill second the throttle cable..same kind of thing happened to me and It would rev up and down pretty often when it was bad without my foot touching the pedal

 

Could be a large vacumn leak. Could also be your TB not closing fully. Try taking your cable off the TB, pulled the TB open then letting it snap closed. Then start the car and see what it idles at. If its still high, use your idle set screw to change it. It is the little tiny flathead screw on the firewall side of the TB close to where it meets the intercooler elbow.