Extremely High Idle on '90 740 GL

I recently bought a '90 740 GL for $200.
It has 176,000 miles on it. When I aquired it, it had been sitting
derelict for the past 18 months outdoors in Michigan.
I've been tinkering with it for the last 2 months.
When I bought it, the Catalytic converter was missing,
which I was told was the only problem it had.
I've bypassed it, temporarily, with a cheap exhaust
repair pipe. I figured that if I got it running, I would spring
for a new cat or maybe an entire exhaust system.

Well, I got it running, but was experiencing high idle
and idle surge. I replaced the wires, plugs, cleaned
the throttle body and replaced the throttle position switch.
I adjusted the throttle body adjustment and the TPS per
instructions I found on Brickboard.com. When I start the car,
the idle soars to between 4000 and 4500 RPM and will not
drop down. When I drop it into gear (it is an automatic) the idle
will drop down to about 1200-1500 RPM. If I switch to PARK
or NEUTRAL, the idle soars back up to 4500.

I've tried more adjusments to the throttle body. I disconnected
the control rod on the throttle body and backed of the adjustment
screw so the butterfly was completely closed. It still idled at 4500.
I loosened up the TPS and clicked it back and forth while the car
was idling. It either stayed at 4500, or surged from 1500 to 2500
when the TPS was out of the idle position.

One question about the throttle body. When the butterfly is closed,
should there be any daylight around the edges? I noticed this when
I was cleaning it. It is not very much. Around the top and bottom
there may have been .010 to .020 of daylight showing. I don't think
that this would let enough air in to cause such a high idle.

I would really hate to give up on this car. The engine seems as solid
as a rock, and the body is built like a tank.

Any info you can provide would be greatly appreciated.
It is a US model. I don't know what ignition system it has in it.

Regards,

Ryan

 

Under the intake manifold is a valve that controls idle speed. You'll
see 2 hoses about 1" in diameter going to it. Clamp off one of the
hoses and see what happens to your idle. Take the valve off and see if
you can clean it up. Note that you can interchange the electrical
connectors between this valve and the throttle switch which blows out
the idle control circuit inside the computer.

 

Thanks for the info. I will try it if I can get the darn thing
started again. After the last run, it was idling at about 3500 RPM
when I shut it off. I have not been able to get it started since. It
keeps cranking, but won't turn over. In the past, I would get it
started by spraying starting fluid into the throttle body, but I have
since found out that this is not a good thing to do.

By the way, does anyone know of a good Volvo mechanic near the Port
Huron, Michigan area. The nearest dealer is about 40 miles away.

Thanks again,

Ryan