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I just bought a 92 mx-3 with the 1.6L sohc it is also a automatic with 174,000 miles.... anyway it had a very bad idle when i bought it but the guy said that the transmission was just rebuilt and when they put it back in they must have pulled a vacume line off... well that sounded about right cause thats how it was acting....anyway i followed all the lines and they are all good, so i did a full tune up and pcv valve, new belts, i also bought a chiltons and learned how to test the (ISCV) and i did that and it's good, anyway the car is idling at about 700rpm's but when it is in drive the whole car rattles and shakes... it runs great but it really does rattle and shake.... any idea's? anything would be great Thanx

Well, the stock idle speed for both MT and AT is 750. If you're around 700, you can try adjusting the air flow on your throttle body, but sounds to me like its more likely to be the transmission. Not positive, but pretty sure the engine would shake pretty bad in neutral if idling low.

And if you adjust your TB, 1/4 turn at a time

does it bounce between 500 and 1500 when you're slowing to a stop? "bad Idle problem" don't say alot lol Mine does that so I searched it on the mazda service tech site and this is exactly what it said. 92' MX-3's with V.I.N's of JM1EC431*NO139355 or lower produced through June 17,1992 ( Letter N in 10th spot) with this problem replace Electronic Control Unit with part Number B665-18-881R. I haven't tried this yet but am really soon and I'll keep everyone posted.

You might have crappy motor and tranny mounts. Even if the idle is good bad mounts will transmit tons of vibration to the chassis. Many Mx-3's and Proteges suffered from this.