Throttle Sensor Adj. EXPERT vs DEALERSHIP

We are discussing an 85 CRX Si. We bought this car in hopes of "fixing it
up" for my son. The drive train and engine have now been completely rebuilt
(because it fell apart shortly after we bought the car!!!) . The car idles
at 1500rpm. The person who sold us the car showed my son the "idle
adjustment screw" that he had been using.. GUESS WHAT that turned out to be
the "THROTTLE SENSOR" adjustment. Let me quote to you from the Honda manual.
" Do not perform any adjustment of the throttle valve stop screw since it
has been adjusted in a very precise and accurate way." The idle screw is in
a different location and is actually completely closed and no more
adjustment is left on it. SO HERE IS THE QUESTION. Do we bite the bullet and
go to the dealership to put this back to factory specs (and pass the
California smog) or do we try this ourselves since we surely cannot make it
much worse than it already is? According to the manual the throttle sensor
adjustment requires interfacing with the PGM-FI SYSTEM computer and a
"SYSTEM CHECKER HARNESS #07999-PE70000" which of course I do not have. Is it
possible to do this without that? The harness just seems to make getting at
the contact points easier. The correct voltage to measure on the #12
position of the PGM-FI harness is 0.48-0.52 volts when the throttle sensor
screw is correctly adjusted.Any experts out there who have insight into this
aspect of the CRX? Thanks in advance for any opinion. wolf

 

Since no one has offered any facts, I'll contribute some opinions.

The throttle position sensor adjustment and the throttle valve stop
screw adjustment are two different things. The latter is a stop screw
that stops the throttle valve from closing completely when you release
the gas pedal. It looks and acts like the idle adjustment screw on many
old carburated cars. The service manual for my '94 Civic states the same
warning, "Only the Gods at the factory should touch this screw"

I did once read a shop manual for a different make of car (I just can't
remember which one) where it was indicated how mere mortals could
actually do this adjustment. From memory:

1. Loosen the lock nut on the throttle valve stop adjustment screw.

2. Adjust the stop screw so that a thin piece of paper just barely can
be passed between the screw and the throttle valve stop.

3. Hold open the throttle valve and tighten the adjustment screw a tad
(i believe it said 1/4 turn) and tighten the lock nut. Then release the
throttle valve.

The idea is that when adjusted properly the throttle valve will be
resting against the stop rather than closing fully, and that this rest
position is very, very close to fully closed.

If you do this, remember to open up the actual idle adjustment screw a
bit before you start the engine.

Let us know if you get things working!

 

I took the car to my local mechanic who basically reiterated your comments.
He adjusted it as you suggested and tested it for the proper voltage reading
(0.5volts if memory servers me). Like you he scoffed at only the "GOD'S at
HONDA" doing the adjustment. He then spent another hour trying to get the
car to idle properly with absolutely no success. At high RPM ie.) > 1500 the
car runs fine. It starts great and while cold is running about 2000 RPM.
Once it gets warm (and at running temp) the idle is like a "sine wave" going
between 800 and 1500RPM at a monotonous pace. This problem existed before we
rebuilt the engine (broken timing belt and trashed valve train) and is now
back to haunt us and keeping us from getting a California SMOG
certificate.We get very little change in idle when adjusting the idle screw
itself but because the idle is so variable it is hard to actually tell what
is going on with the idle adjustment. Here are the things we have done:
confirmed correct timing belt and timed the car. Checked O2 sensor (OK)
Checked for leaks in various vacuum hoses. Made sure the rotor weight turned
freely in the distributor. Replaced PCV valve (boy that was a bear to do in
this car). Things I plan to do. See if any LED's are activated in the
computer (have not looked at the computer yet..may have been dumb not to).
Clean the port where the idle screw sits.Replace the temperature sensor in
the head (the resistance readings on the current one are not like the
factory specs suggest). The car has a new thermostat and it appears to be
working. The lower hose is cold until it kicks open and then it gets warm.I
just adjusted the valves but will do that again. Apparently if they are set
too tight your idle will suffer.
Trying to think about this I thought the problem was "temperature" related.
ie. when the car is cold it runs great when hot it surges between 800 and
1500. In fact it may be "rate" related ie.) "high" idle is working OK "low"
idle is defective. There is nothing I can find specific to address that
problem in this car.As you can see this is not a "novice" problem and I very
much appreciate your input and time. Sincerely, wolf

 

If you have any sort of vacuum leak you can get your symptom of an
oscillating idle speed. After having removed my throttle body I got some
crud on the gasket between the TB and the intake manifold and that was
enough to create problems.

To simplify troubleshooting you can temporarily disconnect the wires to
the idle air control valve (Actually, I think it was called the fast
idle valve on the 85 CRX). That should stop the idle speed from
oscillating during troubleshooting. On my '94 the idle air control valve
is mounted to the intake manifold, just past the throttle body. It
should be in the same general vicinity on your car. Then adjust the idle
adjustment screw to get the idle as close to normal as possible.

I located my leak by using a squirt bottle with iso-propyl alcohol
(rubbing alcohol). Others recommend using carb cleaner. Water would
probably do as well. Squirt around the intake system and you will see a
dramatic drop in RPM when you spray the spot where there is a leak.

If you do not find a leak this way, try pinching all the different
vacuum hoses to see if you can find one that lets the idle drop. If you
can drop the idle by pinching a hose, follow that hose to see if you can
find a faulty valve etc.

Another possibility is that the throttle stop screw is holding the
throttle valve open too far. I do not have any experience or with that,
so the following is speculation only:

Try disconnecting the idle air control valve, open up the idle
adjustment screw and adjust the throttle stop adjustment screw so that
you have a gap between the screw and the throttle stop. Now adjust the
idle adjustment screw to get the idle speed as low as it will go without
the engine stalling. If you are able to get the idle really low this
way, you are on the right track. Leave the idle adjustment screw that
way, and start adjusting the throttle valve stop screw until you can
just barely see a rise in idle speed. Tighten the lock nut at this point
and the throttle stop adjustment should be as good as it gets. Then
proceed with idle speed adjustment etc. On my '94 the idle is adjusted
with the idle air control valve disconnected and the service check
connector shorted. The service manual should give the procedure for your
CRX.

Good luck!

 

WOW you gave me a lot to study! I printed out your message and will work on
this over the next few days. I want to recheck the hoses and will get a good
"spray bottle" to do that. One of the hoses we pinched did seem to improve
things but I need to go back and try to find it again. Thank you very much
for your very helpful ideas. wolf

 

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&threadm=2d61ec%2
4jta%40opel.secondsource.com&rnum=1&prev=/groups%3Fhl%3Den%26lr%3D%26ie%3DUT
F-8%26oe%3DUTF-8%26q%3Dthermowax%2Bplunger%2B%2Bsolution%2Bfound%2Bhonda%26b
tnG%3DGoogle%2BSearch

"A solution has been found! The problem was the "fast idle" valve. This
valve has a thermowax plunger and tubing to cycle coolant. In theory the
valve opens to enrichen the mixture when the coolant is cold. Defective
valves either vastly miss the trip mark or wiggle wildly."

I read this article and it seemed to be worth a "shot" coupled with the
comments you made in your second paragraph below. I had a spare FAST IDLE
VALVE from the old block and although it looked terrible on the outside
when I installed it , IT appears to WORK!!YES!! I just hope it continues to
work. Thanks again for all the good suggestions. Now I can do my Christmas
cards. wolf

 

The link got cut off in the prior post so below is the article in case
anyone wants or needs the information. wolf

I had the same problem with my `85. I had tried several things, then posted
to the net here, as you did. I received help from a Bryce Nesbitt at
commodore.com, who replied with the following. When I did this, though,
the problem did not go right away. However, after a month or so, the
problem mysteriously stopped and has not returned in almost two years,
so here goes:

I posted and received responses from several people that said "my car
does that also and nobody can find a solution either."

A solution has been found! The problem was the "fast idle" valve.
This valve has a thermowax plunger and tubing to cycle coolant. In
theory the valve opens to enrichen the mixture when the coolant is
cold. Defective valves either vastly miss the trip mark or wiggle wildly.

Replacing the valve cost $48.00. My thanks to Richard Thomson Automotive
of West Chester, PA (*The Texaco Station). Richard is good, honest,