Question
after the rebuild
So i have just read a post
http://en.allexperts.com/q/Mazda-Repair-821/2009/5/1990-mazda-miata-rough-2.htm
and i am having the same trouble. i have rebuilt my motor and i have an aftermarket intake, exhaust, radiator, etc.. i know my car inside and out and have built in piece by piece but ive come across a rough idle issue. when cold, it barely idles on its own, dropping into the low 300's and struggling very hard to maintain idle. once hot, it runs like a new car, idles properly, and drives fine. But I am showing the same symptoms as the previous questionee, where when hot, and throttle released, the RPM stops at 1400-1500 (depending on ambient temperature) then after say 15-45 seconds, kicks down and idles at 800 like its supposed to, but it feels like i have a mis fire, and the motor shakes irregularly. ive taken apart most of the obvious mechanical leads, like timing, spark plugs, oil viscosity, radiator pressure and flow, and octane level, but still have this problem. you stated that the ISCV might be the problem, but those are hundreds of dollars and i dont have time for that. mine looks ok, and ive run carb cleaner through the intake to de-gunk it and ive checked multiple vacuum lines and it all points to operator error. **Note** when the air filter is removed and the car is cold started, it runs like it should; actually idles higher than supposed to because of my adjustment on the intake to keep it running, but once the filter is replaced, it does it starts to mis fire again. i used a fuel/air ratio meter to check for any irregularities and it seems to be running rich with the air filter on. another note, i have a high flow K&N Filter charger on a ram air intake by Racing Beat. its very tricky and my Auto shop professor thinks it has high compression pistons in it, and that it will never run the way its supposed to (it was a track car, then retired to pace car, then i bought it after it had years of abuse and neglect.) any help would be amazing, and if you need any information, let me know. i want to pass this car onto my little brother when he graduates high school, but he wont have time to work on it. ill continue diagnostics on it until i figure it out, but i would really like to get it done soon. june is approaching very quickly. a friend of mine said that resetting the computer and allowing the car to relearn how to manage the engine might fix the problem, or damage it further; thats not a risk im willing to take, and it doesnt make sense to force learn the computer because the management system has been pulled and uses very minimal electronic management. the ISCV seems like the culprit, but after some research i learned that it uses coolant flow to hold the valve open. possibly corroded??? would the Mass air flow sensor have any say in this issue? and is there something i might be overlooking? hopefully something easily repaired? its always the stupid things with mazda that make them break down so possibly im overlooking the most obvious of errors. the check engine light is not illuminated, and the code reader has no pending codes, or current codes. i was kind of thinking that maybe its a resistance problem in a sensor?
thanks for any help. much appreciated.
-Jack
Answeryou question is very long an involved, but in saying so the home mechanic should really only concern themselfs with a possible vacuum leak, or improper routing of the vacuum lines. you can normally hear a vaccum leak. using a propane torch with in open but not lite run in around the motor if the rpms increase when you pass it over a certain point your found the leak repair as normal,
a rogh idle can be causes by a number of things a TPS sensor out of adjustment or not working and IAC sensor fault, a misfire, a tear in the air ducting and so on
