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no engine size stated... (impossible to answer in details)
how can idle surge and the tachometer is steady.
that make my hair stand on end. (2 failures)?
surge is caused by the below things
1: ISC out of control or ECU in limphome mode, CEL glowing all the time.
2: engine, fueling wrong, lean, or gross misfire (spark bad)
3: EGR valve stuck open.
ever do a 60k mile tune up, ever. if not why not to it now.?
spark parts , filters?
1: does car drive perfectly
2: fresh fuel not 3 years old.
3: gets normal MPG, ?????
4: is it a daily driver. not sitting long periods, ?
if the tacho, does in fact not reflect true RPM at all times
id like to know that. its very bad,
did the tacho work before? and how long ago.
in any case check all fuses shown in the glove box owners manual
check the MAP sensor (manifold absolute pressure). The ECM (car computer) uses that to keep idle at minimum 750 RPM. It's normal for it to run high when cold. These small 4 banger motors typically run hot, and they won't run right IF they're NOT running hot, ergo the idle is usually high when it is cold so as to cause it to warm up quicker. If the RPM's drop below 750, suspect the MAP sensor, &/or ECM.
The idle adjustment screw in throttle body has carbon build up on its tip.need to remove screw clean depoisits off tip,carbon in idlescrew port(with carb clean) re-install idle screw,seat it,then back out 1 1/2 turns.start car and hold at higher idle to blow out carb. clean &deposits out of throttle body then recheck for surging once warmed up.
well if the idle is surging(going from 1000 to 1500) you probably have air bubbles in your radiator. i had the same problem. just run your car and then fill it with anitfreeze and let it run without the cap on so all the airbubbles to get out.
and if it just stays at a constant 1500 you can just turn the idle down. a mechanic can do it pretty cheap