idle automatically adjust down

I set my idle on my 940 tubro, 1992 to 900 rpm and it is adjusting
itself down to 650 rpm. What my be the problem???

 

That sounds like it is working right.

Mike

 

Thanks! The reason I asked the question I am having a problem with the
car stopping. I the same as if the air filter is dirty but I have a new
filter. I can hit on the hose going from the filter and the problem
stops. I it will start again in day, week or sometimes may several
weeks. It seem to be an air problem, so I thought maybe the computer
because everything else is new. For example, ignition coil, dist. cap
and wires, etc. It runs good like a new car, but then I will get a
warning as the car will drag and ten stop. Fuel pump pressure has been
check and no computer codes at all for anything. I am clueless. Can
anyone shed some light on my problem???

 

Have the throttle body and idle air control valve been cleaned? Normally
that is more of a problem at idle, especially cold idle, but may as well
cover the basics.

Otherwise, there are two common problems that can give those symptoms. The
fuel pump relay comes to mind first - the solder connections that mate the
relays to the circuit board inside the module crack and become intermittent.
Some people pull the cover off and resolder the connections, others pony up
the $40 US or so for a new one. The relay is usually worse when the car is
warm than when it is cold, but mostly it does what it wants.

The "power stage" that drives the ignition coil is also famous for
intermittents when hot, especially the sagging type. The tachometer will
usually drop before the engine speed does, even dropping to zero before the
engine dies. The problem is generally cured by removing the device from the
body, cleaning the mounting surface and even applying heat sink compound
(available at electronics stores or computer shops) before snugly
remounting.

But if it isn't a coincidence that it stops acting up when you whack the
hose to the air filter, the Mass Air Flow sensor, also called an Air Mass
Meter or AMM, could be the culprit. They definitely can become intermittent
and I don't know if they will set the "check engine" light in a '92. Next
time, instead of disturbing the hose, carefully apply upward pressure to the
flat connector on the AMM (that device in the duct right after the air
filter). If the engine surges when you lift, you may get away with removing
and carefully reseating the connector (it worked for me!) If tweaking the
connector doesn't help, try rapping on the AMM itself. They are expensive to
replace but a bad one won't do you any good at all. They are also available
from wrecking yards.

Mike

 

where is the fuel pump relay module???