Idle valve replacement (1994 Camry 4 cylinder - 5S-FE)

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Old 21 Nov 2004, 08:43 am   #1 (permalink)
Daniel M. Dreifus
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Default Idle valve replacement (1994 Camry 4 cylinder - 5S-FE)

After cleaning the idle air control valve for three years, the time
between cleanings began to be reduced, so decided to replace with new.
Online price apx. $171 vs. $230 locally (add $99 plus accessories for
a simple 5 gal. dual tank air compressor to blow out the vacuum
fittings on the throttle body).
Here's where it is essential to have the factory service manuals.
Wound up also cleaning the throttle body, adjusting the throttle
positioner, and adjusting the throttle position sensor, +/- .004".
Since I was only replacing the idle control valve to correct stumbling
cold start up, one might assume the throttle position sensor and
throttle positioner were fine, but since the manual lists various
checks to be performed on and off the car when removing the throttle
body, went ahead and checked.
Surprisingly, the setting for the throttle position sensor (TPS) was
not within specification. The last step is a verification - no
continuity between the lower two contact pins on the TPS (with vacuum
applied to hold back the throttle positioner) - at .028" and with
continuity between those lower two pins at .020". Seems one
essentially is checking the idle control switch function of the TPS. I
had no continuity at .020", so loosened the adjustment screws and
moved the TPS to achieve continuity - then re read the earlier section
and discovered that the initial setting is to be done at .024", then
the final check at .028 and .020 to confirm. So I re set it again,
discovering the handy "continuity" function on the DMM which shows
"OPEN" or "SHRT" on the display and sounds a beep for "short" - which
with the leads clipped to the lower two contacts was actually the
continuity I was adjusting to achieve - made it easier to slowly turn
the TPS until hearing a beep sound.
The throttle positioner is a vacuum operated diaphragm that holds open
the throttle slightly until a vacuum is applied. The on car test with
engine warm, is to run RPMs to 2,500, then release throttle and set
positioner to 1,400 RPM, +/- 100. For some reason, mine was way too
high. Adjustment involves using an 8mm wrench on the adjustment screw
locking nut with very little room to turn it, but was able to get a
bit more working room by lifting the spark plug wires out of the first
Throttle body cleaning:
Can understand now, why Toyota techs remove the throttle body for
cleaning rather than using Haynes carb. cleaner and rag method. First,
the back side of the throttle body, that you cannot see unless
removed, is far dirtier than the front. Seems the EGR port releasing
exhaust, is right behind it. Also, when the throttle body (TB) is
removed, you can see the teensy tiny holes - these things are really
small - tiny, tiny holes that correspond to the vacuum fittings on top
of the TB leading to the EGR vacuum modulator. Spraying carburetor
cleaner through the fittings released a dark residue from the small
openings in the TB throat. Also, of the two the idle air control valve
(IAC) passageways, one had a lot of black color, though minimal
buildup. This too, could only be cleaned by removal of the IAC valve
after removing the TB. There was also a groove on the back of the TB
with the black residue. And wiping with a rag, was able to remove
quite a bit of black greasy residue from inside of the intake plenum
directly behind the TB.
BTW, covered the TPS with plastic prior to cleaning the TB with
solvent spray.
One more note, on the prior day's maintenance work, along with oil
change, the factory manual lists specifications for accessory belt
tension, and recommends checking regularly. I use a Burroughs belt
tension gauge from eBay for the alternator/ AC belt, and a smaller
click type belt tension gauge for the power steering belt. The A/C
belt takes 130 lbs., +/- 10 lbs., and the power steering belt 80 lbs..
Both were loose and required adjustment. Thought I had tensioned the
power steering belt about as tightly as I could 5,000 miles ago when
replacing, but current reading was around 40 lbs. Discovered that by
using a large screwdriver and prying against the adjustment bolt in
the elongated slot, was able to exert sufficient pressure to bring
belt tension up to 70 lbs. The A/C belt had been tensioned to spec
when new, but also needed extra tightening. Using that Burroughs belt
tension gauge has got to be the slickest way possible - one simply
observes the disk with markings rotate and align the correct value
with the pointer while turning the adjustment bolt for the belt.
Frankly, don't see how these belts can be correctly adjusted without
the use of gauges.
Smoothness of operation and power both seem improved after this work.
Could be subjective, but in any event, car drives beautifully. Gave me
an appreciation for the work the Toyota techs perform if they actually
do the prescribed work from the service manual, IAC valve replacement
and TB cleaning and adjustments would be worth the $350 I've seen
referenced here.
Speaking of Toyota techs, one final footnote. While removing the
screws holding the IAC valve, I used a hand held impact wrench
operated with hammer strike to the end to loosen Phillips head screws
without stripping them. Had acquired this tool many years ago for
removing stuck screws from motorcycle cases. Anyway, the first three
of the four came out effortlessly, but the fourth screw head became
hopelessly rounded such that the "cross" in the middle turned into a
nice little circle. After removal with vice grip pliers and a trip to
Toyota parts dealer for replacement, they could only special order.
Not sure this procedure is accepted practice, but walked back to the
service bays with stripped screw in hand - after being declined by the
first mechanic, a kindly second mechanic nearby asked about the
problem as I began to walk away and wound up finding an exact
replacement from his extra parts bin and grinding and buffing the
threaded end to match length. Very nice work on a critical fastener -
much appreciated.
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Old 21 Nov 2004, 06:33 pm   #2 (permalink)
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Default Re: Idle valve replacement (1994 Camry 4 cylinder - 5S-FE)

Sounds like a satisfying day's work. While I would not attempt the TPS, I
had thought about removing the TB to clean it. A few questions: do you
need a new gasket when you replace it (does Toyota stock these?)...Haynes
says to drain the coolant--necessary? Must you prevent carb cleaner from
touching the TPS or IAC? Besides getting black gook off these components,
are there performance benefits?

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Old 22 Nov 2004, 08:42 am   #3 (permalink)
Daniel M. Dreifus
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Default Re: Idle valve replacement (1994 Camry 4 cylinder - 5S-FE)

"camry-keeper" <> wrote in message news:<4208c49ad825ec61250081b9027e14fa@localhost.t>...
> had thought about removing the TB to clean it. A few questions: do you
> need a new gasket when you replace it (does Toyota stock these?)...

Yes. Toyota manual calls the gasket a "non reusable part", should be
in stock at dealer for around $2.

> says to drain the coolant--necessary?

Wondered about that myself (how much could spill out), but decided
since that is listed in the factory repair manual, should be done.
Discovered it's fairly easy to open the radiator drain plug from above
with finger pressure, then a little spout directs the coolant through
a hole in the plastic shrouding beneath. No need to lift the car,
crawl under and unfasten all those small bolts as I'd done before.

Must you prevent carb cleaner from
> touching the TPS or IAC?

Yes. Manual says not to spray carb cleaner on the TPS. You'll probably
be removing the IAC for cleaning anyway. New gasket there is under $1.
The TPS is over on the side, just don't spray there. Plus I covered it
with plastic held in place with a stout rubber band.

Besides getting black gook off these components,
> are there performance benefits?

I always had a slight hesitation just past 1/4 throttle - very mild,
but a noticeable slight jump in power just after a certain point.
Bought the car used, with IAC already replaced by the dealer, and
assumed that was a function of the power band or camshaft design since
it always did that - but no more - accelerates entirely smoothly now.
Also, naturally, since replaced with a new part, cold idle is
improved. Surprisingly, cold idle is _lower_ than before - apx. 1k rpm
instead of 1200, but always correct for conditions. Plus, obviously,
no worries about not idling properly when first starting in the
morning with a need to manually press the accelerator to avoid dying
or jerky uneven too low idle - which is, of course, the reason for the
work being done.
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