Funny Idle but only in 1st and only sometimes....? help

[Posey24]

well i gots a 92 MX-3 1.8 V6... got CAI and thats bout it... 204K miles on it... when the car idles on its own its fine but when i put it in first it will build idle up to bout 1500-1800 then drop to like 500 then build back up... but only sometimes... cold warm.... doesnt matter... any thoughts if u need more info let me know...

[Pritchett]

Mines does the same thing sometimes...but usually only when the engine is warm

[Ryan]

What do you mean put it in 1st?

As in, select first gear, holding the clutch disengaged, or cruising in 1st?

[Posey24]

Clutch in chill in at a light waiting. Any thoughts?

[davmac]

If clutch pedal is pressed to the floor then what you’re saying is that idle is surging sometimes and has nothing to do with the position of the shift lever. Chances are you were just driving and the engine RPMs were much higher just moments earlier. Is check engine light on? If no check engine light then check the throttle cable at the throttle body to be sure it is not binding and the throttle snaps completely shut when there is no pressure on the cable. It is a good idea to remove and thoroughly clean the throttle body, check the throttle position sensor and reset it according to service manual. If the throttle body is very dirty you might also remove and clean the idle air controller (attached to the bottom of the throttle body).