Temp gauge dead/ idle issue

When my 91 Integra is idling, the RPM's are going up and down from 1500-2200 RPM,....like it the car is breathing....:). This started just this weekend. Also noticed my temp gauge stopped working when this
weird idling began or maybe the weird idling started when the temp guage stopped working. The temp needle stays on C, never raises to operating temp. I also noticed the heater air temp, is not as warm/hot as it normally is. The car runs fine other than the weird idling.
I suspect a faulty temp sensor/sending unit or a faulty thermostat, causing the idle issue.
What do you think Tegger?....or anyone else.
THANKS!
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B.Creech wrote:

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As Groucho said: "Why, a four year-old boy could understand this".
Your reservoir and radiator are mostly empty. Don't drive it anywhere or you might crack your head. Fill them both with Honda premix and then keep topping up the reservoir to the MAX mark for a couple more mornings until is stops 'sipping' coolant as the AIR is purged. It will solve your immediate problems. There's more to purging air from a '91 Teg, but this will get you out of the woods.
'Curly'
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motsco_ wrote:

I guess I should have mentioned, I check the obvious Friday when the symptoms started. The radiator and resevoir are full.
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B.Creech wrote: > I guess I should have mentioned, I check the obvious Friday when the

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Then it must be just AIR, since the sensors have to be immersed or they will give the symptoms you describe. Are you sure nobody has been working on your cooling system recently ?
'Curly'
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This affects idle only on Accords and Preludes and other F-series engined cars on account of the system's design.
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Only when hot, right?

I'd suspect a faulty thermostat before anything else.
The ECU and the dash gause use different sensors. It would be unlikely for both to fail at teh same time.
Try replacing the thermostat with new OEM. Do not use aftermarket.
As for the dash gauge... the sender is a single-wire unit under the distributor. Make sure that's hooked up and the wire isn't broken.
Fluctuating idle can also be caused by neglected coolant changes. The Fast Idle valve sticks open, leading to excessive air when hot. There is a way to test for that.
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No. I first dicovered the issue Friday when I went to lunch. Cranked the car....cold... up and down idling. When car gets hot, no difference. HOwever once, while driving the weekend, I noticed the temp needle had started working and was registering normal operating temp. When I stopped at stoplight, car idled normal.
This temp gauge starting to work only occurred once all weekend.
Tegger wrote:

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on my 94 Integra GS-R,I had to replace both thermostat and ECT;the temp sensor(on the thermostat housing) ohmed out as open. My dash temp gauge read fine.
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Jim Yanik
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Jim Yanik wrote:

I was mistaken when I replied earlier the problem occurred when the engine was cold also. Today I have found that the bouncing idle issue only occurs after the engine gets warm a few minutes after starting, at the same time the temp gauge is not working...reading C. Again today the temp gauge started working while I was driving. When I came to a stop, the car idled just fine. That is the second time I have seen this happen.
I am still inclined to believe the temp guage not working is related to the bouncing idle issue. I guess I can start by replacing the thermostat, probably the cheapest place to start
The coolant was changed in the vehicle about 6 months ago when I had the timing belt and water pump replaced, so no coolant neglect.
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Why? The temp gauge is not connected to the ECU in any way. The ECU uses a separate Engine Coolant Temp(ECT) sensor.(2-wire thermistor) The gauge temp sensor is a one-wire sensor,and not in the same location.

while you have the TS housing off,you might as well measure the engine coolant temp (ECT) sensor resistance.it should read 2000 ohms at 68 degF.(mine read 0;open) at boiling,it should read ~400 ohms. Those numbers are from my 94-01 Integra Haynes manual)

Some Honda motors(like my 94 Integra B-18 motor) have an air-bleed port to remove all the air from the block. If the coolant is not covering the ECT,it can cause idle problems.
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Jim Yanik wrote:

Hey guys, could it be bad or dirty IACV?
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Do you have an automatic transmission?
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Tegger wrote:

It is a 5spd manual.
Just drove the car out to dinner. On the way there, the temp gauge worked, and car idled just fine. However, it seems the temp guage maybe registering slightly cooler than usual.
On the way home, temp gauge tried to register, but never left just about the left had mark. Idle bounced slightly, but not as bad as earlier today.
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I'm frankly at a total loss to explain the apparent connection between your temperature gauge and the bouncing idle.
The temp gauge/sender and the EACV are on totally different circuits, with different fuses and connectors. The EACV is the ONLY electrical component on your car that has anything remotely to do with the idle.
I can only conclude that 1) it's a bizarre coincidence, 2) there are aftermarket intrusions into the wiring which are poorly made, or 3) there is corrosion on the ECU connectors, causing shorts between wires there.
Have you looked at the ECU to see if it's nice and shiny clean?
With the idle fluctuating, remove the air intake pipe from air cleaner to throttle body. Cover the LOWER port in the throttle body with your finger. Does the idle settle down?
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And have you checked the ECU for stored codes?
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Tegger wrote:

No I have not checked ECU stored codes, will do that tomorrow.
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Tegger wrote:

Update.. no stored ECU codes. After today, I am now convinced it is probably the thermostat. Today when driving going to lunch the temp needle moved off C a little bit. The bouncy idle was alot less when stopped. On the way home, the temp needle eventually moved up to normal operating temperature, no bouncy idle at all.
Suspect thermostat is intermittently sticking and causing engine to run colder. Now do I change it myself or take it to my mechanic. I have read on the Acura forums the 3 bolts to remove the thermostat are a bitch to get to. Some have changed it in 30mins, some 2hour+ due to the bolts.
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It's pretty easy, actually. I think those "2hour+" reports may be the experiences of less-than-qualified individuals.
The only real problem is that room is a bit tight. You need to remove the big black air intake pipe for access.
That third bolt is for the ECU ground; the other two bolts actually hold the housing on. They are diametrically opposed; the third one is towards the top.
The bolts are 10mm or 12mm, as I recall. One will take a socket, the other may need a short wrench. The kind of wrench that has a a ratchet in the closed end is very helpful.
Use a worn screwdriver to scrape corrosion off the lips of the housing halves before you install the new 'stat.
If you're even remotely mechanically inclined, this is no more difficult than changing your own oil.
A tip though: Use an OEM thermostat and gasket!!!!
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