Two Problems: Temperature and Idle speed. C4

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
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SteveC wrote:

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
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Two of those issues, idle and fans are under control of ECM. Have you tried 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

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George Csahanin wrote:

George brings up a good point on the throttle 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
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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.
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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
wrote:

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.
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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
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wrote:

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
--
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
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The 94 is a different engine, though same principle applies.
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:
http://www.autozone.com/autozone/repairinfo/repairguide/repairGuideContent.jsp?chapterTitle=Trouble+Codes&partName=Driveability+%26+Emissions+Controls&pageId 00c1528008fddd&subChapterTitle=Reading+Codes&partId    00c1528008fc1e
You need to setup a "membership" to access< maybe.
Else I'll e-mail it to you, how to and the codes.
GeorgeC
wrote:

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