Two Problems: Temperature and Idle speed. C4
SteveC
1800 RPM. After driving for 2 minutes or so, the idle speed can be as
high as 3500 RPM. I can go about 35 MPH while idling the engine. How
can I adjust the idle down to normal? Any ideas?
Second issue. Radiator cooling fans don't seem to be working. I've
determined that the fans themselves are OK, but for some reason they
are not turning on. Obviously, the engine runs real hot on hot days.
I need to fix this. Any ideas on where to start looking?
Thanx in advance
pj
I'd look at the idle issue first as, with the
right info I think it's more simple than the fan
issue. (And if you find a bad connector around
the ECM that might fix the fan problem.)
Fans could be sensor issues, ECM, relays or
wiring. The sensors include temperature,
vehicle speed (mph) a/c compressor on/off. All
that goes into the ECM and it turns-on the fan.
Hi-temp: Check for road debris or insects in
the a/c condenser or radiator.
The idle issue could be the idle air valve, ECM
or wiring. Idle isn't a screwdriver adjustment.
On engine start the ECM cycles the idle air
valve, finds a zero point and steps it upward to
meet a pre-determined idle then it steps it
downward as the engine warms up. You can't alter
what's built into the ECM. There's a position
sensor on the idle air valve and you can tell if
it's moving by measuring the voltage coming from
that sensor. Sometimes the valve gets gummed up.
Follow tech manual cleaning instructions as
you can ruin the wiring in the stepper motor or
position sensor with typical solvents.
In tackling these, a Haynes is a bit of a help
but the troubleshooting charts in the factory
manual will get pay for themselves in time
saved. 1990 had fuel injection differences from
both 1989 and 1991 so get the right manual.
Item: ST36490 -- $ 157 includes supplements &
electrical troubleshooting guide
From: http://www.helminc.com
hth
--
pj
George Csahanin
to get error codes from the ECM?
As PJ said, no adustment for idle, that is set by IAC valve, but a vacuum
leak can sureley do that as well, if it lets outside air into the manifold,
which is pretty much what the IAC does.
When it idles that high, what position are the throttle plates in? Are they
mechanically being allowed to open?
This has many possible causes.
GeorgeC
"SteveC" <steve...@aol.com> wrote in message
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pj
assy. and all the vacuum connections to the plenum
When I posted I forgot to mention that above
40-45 mph the fan isn't doing much and ram air
takes over. If you're running hot at 50-55,
check the thermostat inside of hoses etc.
Water pump OK and no "weeping"?
--pj
a
SteveC
After checking and cleaning all connections things seem to be getting
better. The drivers side radiator fan now works, but I have yet to
witness the passenger side fan operate. AC on or off. I drove around
for about a half hour and the idle did not climb to 3500 RPM as
before, and I seem to have picked up a few horse power. The idle
hovers around 2000 RPM when at stop and in neutral and around 1500 RPM
when at stop and in gear. This still seems too high, but I'm not sure
I trust the dash panel tachometer.
George Csahanin
closed for idle, and/or chack throttle position sensor for proper operation.
I can be remembering incorrectly, but it is fed with 5 volts, I seem to
remember, and at idele it should be around .7 volts.
I think the Haynes book has a setup on it.
but check the vacuum lines that source at the intake manifold. A leak there
will do this. Easy fast check is to pinch off any hoses that go there, and
see if the engine idles down.
Also, second fan only comes on with high temps or high a/c head pressure.
But exact memory is hazy on it.
GeorgeC
"SteveC" <steve...@aol.com> wrote in message
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SteveC
> Does the throttle linkage look like it is binding, or not going to fully
> closed for idle, and/or chack throttle position sensor for proper operation.
> I can be remembering incorrectly, but it is fed with 5 volts, I seem to
> remember, and at idele it should be around .7 volts.
>
> I think the Haynes book has a setup on it.
>
> but check the vacuum lines that source at the intake manifold. A leak there
> will do this. Easy fast check is to pinch off any hoses that go there, and
> see if the engine idles down.
>
> Also, second fan only comes on with high temps or high a/c head pressure.
>
> But exact memory is hazy on it.
>
> GeorgeC
>
>
> news:bf9df121-b4eb-472c...@e34g2000vbm.googlegroups.com...
> On Sep 3, 8:49 am, SteveC <stevec1...@aol.com> wrote:
>
> > RE: 1990 C4 convertible, automatic trans. My idle speed is around
> > 1800 RPM. After driving for 2 minutes or so, the idle speed can be as
> > high as 3500 RPM. I can go about 35 MPH while idling the engine. How
> > can I adjust the idle down to normal? Any ideas?
> > Second issue. Radiator cooling fans don't seem to be working. I've
> > determined that the fans themselves are OK, but for some reason they
> > are not turning on. Obviously, the engine runs real hot on hot days.
> > I need to fix this. Any ideas on where to start looking?
> > Thanx in advance
>
> After checking and cleaning all connections things seem to be getting
> better. The drivers side radiator fan now works, but I have yet to
> witness the passenger side fan operate. AC on or off. I drove around
> for about a half hour and the idle did not climb to 3500 RPM as
> before, and I seem to have picked up a few horse power. The idle
> hovers around 2000 RPM when at stop and in neutral and around 1500 RPM
> when at stop and in gear. This still seems too high, but I'm not sure
> I trust the dash panel tachometer.
Hi George,
Thanx for the input. The idle still climbs on occasion to around 3500
RPM. If I shut the engine off and restart it, the idle calms down to
about 1500, and may or may not climb back up after driving. Does that
make any sense to you? Is the input air control valve sticking? I
think the throttle position sensor is OK. I recently replaced all of
the injectors, but I doubt that has anything to do with it.
Steve
charlie
---
i had this occur on my 94. i thought the iac was sticking so replaced it. no
change. i tracked it down to a crack in a 1/2" plastic tube that runs under
the right plenum cover from the top back of the engine to just aft of the
iac. when it warmed up, the crack would open, causing a fast idle. after the
engine cooled, the crack would close, and the problem would disappear.
i don't know of the 90 has this same rebreather tube.
regards,
charlie
cave creek, az
George Csahanin
Steve, it could be IAC valve, or control thereof from the computer. HAve you
looked for stored codes? That could cut down the head scratching. Its pretty
easy in a pre-OBDII engine. I have done that with my 92, though have Diacom
software and adapters that make it readout on a PC, also use a Actron
device to get info from the engine's serial data stream, which the 90
probably has too.
From AutoZone:
You need to setup a "membership" to access< maybe.
Else I'll e-mail it to you, how to and the codes.
GeorgeC
"charlie" <chan...@nospam.yahoo.com> wrote in message
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