Question1991 Toyota Landcruiser, automatic, with A/C.
Sometimes when the engine is started warm,
the idle is irradict and oscillates between
400 (almost dying) and 1,800 RPM at a frequency
of about 2 seconds. Eventually (after 1 minute),
it settles down, but steady idle is too high
(about 1,200 RPM). The symptom only occurs when
the truck is started when hot/warm, and most
often occurs after car has been turned off
for less than 1 hour.
Another thing that sometimes occurs when it is
started when hot/warm is that the idle is steady,
but too high (about 1,200 RPM). When this
symptom occurs, the neutral start switch causes
the idle to jump up 500 RPM! I can kill the
engine by putting it in Park, then in Drive
without stepping on the gas. The idle speed
drops so quickly and so much that the engine
dies.
Once either of these symptoms occur, the truck
is often easy to stall during initial
accelaration. Allowing the truck to completely
cool before restarting stops the symptoms.
I removed the Idle Speed Control valve and cleaned
it thoroughly, and put on new water hoses. I have
not yet removed and cleaned the throttle body or
the air flow meter. However, the throttle body was
"cleaned" at a dealer recently (but not removed)
with a cleaner treatment when new ignition parts
were put in.
The cold start injector has been disconnected
electrically. This did not solve the idle
speed problems. However, this did solve another
problem where the engine would frequently die on
accelleration when started while warm (even when
none of the idle speed symptoms occurred). A
dealer tech's suspicion was that the injector leaks
when activated warm. I think it might be the
cold start time switch, instead. Anyway, for now,
I have disconnected the cold start injector and
the engine doesn't die. But, I still have the
idle speed problem. I suppose it is possible that
the cold start injector is leaking when hot, even though no electrical signal turns it on, but I think this is
unlikely.
When I cleaned the ISC valve, I did not take apart
the plastic part of the valve. I removed the
metal flange with the water hose attachments from
the plastic part and cleaned everything thoroughly.
But, it looks like the plastic part is not designed
to be taken apart. One of the three plastic pins
holding it together is loose and it looks like I
might be able to open it, but I'm not sure I should.
After cleaning, the various idle speed compensations
became more consistent, but it didn't solve this
main warm start idle speed problem.
Since it appears that the coolant temperature sensor
is the same sensor used by the dash temp gauge, which
seems to operate within normal temp ranges, I am
assuming that the water temp sensor is working fine.
Questions:
1) Should I take apart the plastic part of the ISC
valve and clean inside?
2) Is is likely that the ISC valve needs to be replaced
(ouch, at $460)?
3) Can you think of anything else I should check that could
be causing these hot idle speed problems?
Thanks for your help.
Tony Williams
AnswerThe answer to question 1= NO.
the answer to question 2= maybe
the answer to question 3= there may be a vacuum leak at the intake manifold or an intake side leak, this could be the intake air hose, it may be cracked,is there a check engine light on? When this idle fluctuation takes place check for an intake manifold gasket leak or other intake leak by spraying some carburetor cleaner around the intake manifold where it connects to the cylinder head, if the engine rpm changes the gasket is probably leaking, another possible problem may be that the egr valve is staying partially open at idle, the egr valve should be checked by applying vacuum with a pump to activate it and release it, if the valve is sticking it will create a low rough idle even after vacuum is removed.
