Hi guys. I have a 1993 NZ new Galant and the other day when I started it up, the revs at idle were higher than normal and 15 seconds later, it started revving up and down all by itself. I turned it off and restarted the car, and all was back to normal. No warning lights came on the dash and drives perfect. Do you think it is the air flow meter or temp sensor or something else? Thanks.
bigfatmat1,
Oct 26, 5:34am
Msg likely cause is a air leak after the afm
franc123,
Oct 26, 9:59am
Galants of that era didn't like low voltage events, ie battery voltage dropping below the 9V region during cranking, might be time for a test to see how well its performing. It sounds stupid but the engine computers sometimes lost the plot when this happened and would temporarily forget how to idle properly.
phillip.weston,
Oct 26, 1:22pm
What generation and what engine? 93 NZ-new could be very last of the 87-93 shape or start of the rounder 93-97 shape. If it's a 2L engine, is it a SOHC 8V (distributor near the cam belt side of the engine), SOHC 16V (distributor on the gearbox end of the engine) or a DOHC 16V (no distributor at all)?
To me the revving up and down is a sign that the idle stepper servo/motor is at max adjustment to compensate for the build up of muck around the throttle plate. I would take off the air intake hose and clean out the throttle body and reset the stepper motor (pull EFI fuse, or just disconnect battery for an hour).
yz490,
Oct 26, 6:52pm
Had that with my Honda. Water pump was leaking--which i new-- but sat for a week & looks like it got below the sensor. Started it & idled way up, so high it would [ or sounded like] it would cut the ignition then cut in again at idle--up & down up & down. Had an idea why so--no obvious water--topped it up & all good straight away. Has a censor in by the thermostat by memory. Not sure if relevant to this case but sounds similar! .
phillip.weston,
Oct 27, 1:41pm
Common with Hondas but not with Mitsubishis. Their sensor is on the thermostat housing which is well below the highest point of the cooling system. Mitsubishis of that era also use a coolant fed wax element to manually control idle speed when cold and have a stepper motor/servo to make fine adjustments (like A/C on, P/S on full lock etc). Surging on a Mitsubishi is almost certainly a stepper motor on max adjustment, or it is just faulty.
christin,
Dec 28, 3:02am
I had that, just before the alternator went. The alternator was on its way out I think, but suddenly when stopped at lights etc it reved one day. Stopped for lunch at parents. Got back in, the reving had stopped but engine light was on. Turned out dead alternator
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