When first starting up the engine idles really funny the needle moves up and down alot around 1500 +/- 400. Though a quick small stab to the gas fixes the idle. Once the car is warm idles fine to.

The engine runs really strong. Any ideas of what's up? also when I free rev the engine I noticed that if the revs climb slowly when I use the gas, the rpm's get knocked back down a bit around 1500 rpm.

Bad vacuum line? Bad ground? Other wise like I said she runs great! Thanks for anyones input.

 

could be a vacuum leak, I kind of doubt it's a bad ground causing THIS issue however you certainly could have bad grounds. could also be your TPS, search for how to adjust it (or there may be a link to a writeup in the FAQ). cruddy idles are a common problem, there should be plenty of information on it. I'm still battling mine, but it got a lot better when I adjusted my TPS back to spec.

 

Cool Thanks I'll research the TPS a bit.

 

check the tps to see if its in spec. If not that or any vacuum leak, it can be throttle body related such as the thermowax, dashpot, etc. When I had this problem, it was the dashpot, and also the thermowax.

 

The funny thing is that it stabilizes with a quick and slight throttle application. Thought the slight RPM fall still happens at 1500 when free revving. I'll take a look at your advice as well.


Darn the FAQs doesn't give specifics on adjusting the TPS. I'll search around a little more, if anyone happens to stumble on anything please let me know, thanks.

 

Here's a good writeup, make sure you do the LED test because you'll likely get poor results only adjusting it by resistance. I know I did. Also, if you have a turbo model the green plug is to the driver's side between the TMIC and AC compressor and not where it shows in the picture.
http://howto.globalvicinity.com/gv_w...i=58&co=1&vi=1

 

99% of bouncy idle problems are a bad AFM... clean it out and make sure it's level and that usually fixes the problem. S4 FC3 and NA3 Miatas are notorious for this same issue.

 

Thanks guys it's an S4 N/A. I think it's prob the TPS, but good to know the other options.

AFM = Air Flow Meter?

 

yes afm is airflow meter, my car has the same problem with having bouncy idle but mine is streetported , 5/6 ports all removed, and ported tb. I think mine has to do with my tps setting and possibly the afm but I dont know.

One problem I do have though is I think my brake booster is going, because when at a stop the more pressure I put on the brakes , the idle will drop more and more to the point where the car is barely idling.