1995 toyota 4runner 4x4 Idling high sometimes than idles real low too
rule 1 on all otto cycle gas engines.
idle is the last thing to work right.
on EFI , its under control at all times.
but if the engine runs bad, it goes out of control.
IS THE CHECK ENGINE warn, lamp glowing running, ????
yes, why not get the DTC codes, (flash error codes now)
when it runs bad, is it misfiring, and shaking engine, weak power from engine,, bogging, or only stalling.
low rpm is near stall and is same thing.
1500rpm is perfectly normal for any cold engine.
Hot , its not.
first off check all fuses.
The idle controls are called ISC, "idle speed controller"
its a slave valve and ECU logic and servo controls.
the ECU works overtime , keeping idle right.
if the ISC sticks, it fails.
if the EGR sticks open , the ISC loses control
if the you get intake (induction) air leaks it loses control
same for misfire, gross, flooding. same for gross lean.
so how do we do this? find a cause.\
easy we give that long missed 60,000 mile tune up.
and during that i clean the ISC and EGR main valves.
on any old car like this, wow, its sure to be a mess, if not serviced.
then make sure the EGR main is closed,
engine hot.
i see if my ISC is trying to work.
i then check my fuel mixtures. to see if the engine EFI
reaches and holds closed loop.
oops, it cant be cause the 0xygen sensor died, 100k miles ago.
its dead.
no OTC scan tools for 1995 ( sure hackers have em)
so is very hard to get this information, i use a scope to watch my oxy sensor, if stuck rich i fix that first. if stuck lean , i find the exhaust crank causing it. or other cause... long list of tests.
in a real shop the start at the tail pipe end, OMG this puppy is rich as a pig and work forward, is start at the oxysensor
i get it working by any means.,
then fix idle if not already magically working. as most do (cleaned)
here is a very common example.
1: EGR sticks open at idle. IDLE RPM drops like rock. ( it must)
2: ECU sees illegal RPM and opens the ISC fully, to no avail.
some cars EFI hunts the ISC causing surging.
others ECU just slams the ISC wide open and does a software hope thing. in this case, does nothing,due to gross EGR misfire effects.
the idle controls are a SERVO,. a closed loop servo system.
it regulates idle until , something horrible happens.
it fails when conditions are outside it's range of Authority.