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When I first start up my 95 Civic and the engine is cold, or has been parked for longer than 20 minutes, it will idle very weird. Without touching the gas pedal it will rev up, then down,then up, then down, and almost stall sometimes. When I begin to drive off the engine starts to bog down, like it's getting way too much gas so I have to take my foot of the pedal then tap the gas pedal down until it starts to bog down again and repeat...I have to do this for about 3 stop signs down the street and then all of a sudden it runs perfect!?

All of this started to happen after I drove my car for about 5 minutes while it was overheating (that's a whole other mystery). After reading some forums online, I went out and bought a new coolant temperature sensor and replaced the old one...to no avail. If anyone has any idea what could be wrong I would appreciate any helpful information. THANKS SO MUCH!

(Some more info: There isn't any black smoke or abnormal emissions,on long trips my coolant overflow tank will fill up and not drain back into the system, and my car used to overheat after long trips but since I was lucky enough to get this mystery problem, it doesn't happen anymore.)

 
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Sounds like you got some problems haha, well to touch on one issue the overflow tank filling up and not returning to your cooling system would be a good indication of a faulty radiator cap (or coolant leak which would allow no vacuum for return).
When the coolant gets hot it expands pushes spring open (in radiator cap, overflow in valve) and leaves into the overflow. When it cools down there is another circular piece (which would be the first part you touch, when holding the cap, and touching the other side or bottom of cap) which comes out. This piece pops out (sometimes sprung sometimes unsprung) due to vacuum from cooled down coolant. Take off your cap when its cool and see if you can pull down the middle circular piece (or overflow return valve). If it doesn't move, then your coolant can not return after cooling down and you need a new cap . This will also cause your hoses to look like they are collapsing when your car starts to cool down.

To explain the overheating on long trips it goes as follows:
The load on a cooling system in city driving is generally not that great. So you can live with a half clogged radiator in city driving. Once you put a load on the system (highway driving which people normally think of as easy driving, but bare with me) you can only cool so much coolant with a faulty/clogged radiator on the highway. To fix that (if your 100% on highway overheating, and fine at the stop light) you will need to replace your radiator.

With all that said I have a guesstimate on your mystery problem. Its a shot in the dark but its just a theory not a diagnoses lol.
The faulty coolant cap damaged one of your hoses (since they're old and starting to weaken) from repetitive hose collapsing (looks like sucking on a straw with your finger on the end). This caused you to start leaking coolant and overheating. You may or may not have put "radiator stop leak" which would have successfully helped clog some of your radiator arteries, which just added fuel to the fire, and eventually you now have a failure in the head gasket somewhere, and there's not enough coolant in the car to reach the temp gauge (which would explain why "its no longer overheating" lol) but i could be off by a mile.
If there's anymore details in a response leave every little detail possible.


P.S although only my 2nd post you can trust my judgment i have credentials lol, not tryin to toot my own horn but not talkin out my a$$

 
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Here it goes...

 
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Hi, thanks so much for responding! I'm going to go through your post and address the issues with as much details as I can, I'll number them too so it's a little easier to follow.

1. When I first bought the car, it started to overheat when I was driving out of town and after trying to figure it out, I found that the previous owners put the wrong size radiator cap on. So, I bought a new one from autozone. This seemed to fix the problem until I started going up hills. I would pull over, see the reservoir tank full and just dump a little out. This seemed to work although it was a little annoying. When I came back to San Diego (from Reno, which is about 500 miles) the car didn't overheat so I thought the problem was solved. About a month later though, the car overheated just from driving 15 miles on a hot day. If I was on the freeway, driving around 65, it wouldn't overheat, the needle would only start to go up after I got off the freeway and was stuck at a red light. After I got to my friends house I put some coolant in the radiator and dumped some out of the overflow tank. This kept it from overheating until I went back up to Reno about a month later. It overheated constantly, but only if I went under 70 mph. In other words, the needle would be in the center as long as I was driving fast but as soon as I got behind a semi, and started to slow down (even to 60 mph), the needle would gradually go up until it went all the way up. Oh, I forgot to say that I have NEVER found any coolant under my car in the morning...so that adds more of a mystery to me, where is the coolant going?? (My guess is there is a small leak in a hose and when my car heats up it slowly starts to leak.) Anyways, back to the overheating roadtrip...I would stop every hundred miles, let it cool down, and fill the radiator up and dump out the overflow tank. On the way back to San Diego I did an experiment (not the smartest experiment someones ever done, but ehh) and drove the whole way without popping the hood. I would stop occasionally to let it cool down but I never put any coolant in it. This worked alright until I got about 30 miles from my house, the needle just went haywire, it would shoot up, then go back to the middle and back up no matter how fast I was going or if I turned the heater on. When I got 2 miles from my house, it's all stop signs and stop lights, the needle stayed way up there and was in the red. I drove it like this for about 5 minutes until I got home ( I know you're never supposed to do that but after a looooong trip, I had to get home.) The next day, I filled it up with some water and it hasn't overheated since, that was about a month ago, but know I have a new mystery problem...

2. Your guesstimate was one of mine as well, however, there is no fluid leaking when it's parked, I also have never put "radiator stop leak" in it, and when I check the oil, there is no grit or foam and it's not watery, so I eliminated the guess that it was the head gasket. Also, when I replaced the coolant temperature sensor a couple days ago there was coolant dripping out when I took the old one out so I know the coolant is reaching the sensor. Oh, and I'm not sure if this is relevant but the fan always kicks on so I know I don't have to replace the coolant temp. switch.

3. Back to the mystery problem (I hope you are still awake and didn't start drooling on your computer by now, haha)...it started right around the time I got back from my last trip to Reno, so I'm pretty sure when I drove the car those 2 miles hot it fried something. I'll try to explain the symptoms as detailed as possible without trying to type sounds, haha. When I turn the car on in the morning and let it warm up, it idles by itself. I'll be sitting in the car with my foot way from the gas and it sounds as if I'm pressing on the gas, then taking my foot off. This happens for about 3 minutes. When I go to drive, the car "pulls back" when I press on the gas, like it's getting too much gas. (And this happens no matter how long I let the car heat up for) I press on the gas again and it acts normal then pulls back again. I do this for about 5 minutes and then all of a sudden something in the car magically heals itself and it runs prefect!? It will run with no problems until I park it for longer than 15-30 minutes...if I do, it does the whole "pulling back" thing again. My guess is that something that controls the air/fuel ratio is off, and that that something got fried when I drove it hot...any ideas on what that something is? I'm pretty sure it's going to be something relatively simple to fix because it only does it when I first drive the car, I'm worried though that it will turn into something major soon, which cars love to do...turn a $5 problem into a $500 within weeks.

So there it is! Sorry to bore you and I want to thank you in advance for any help or advice you have. I'm broke, very broke, so I can't take it into the shop so I'm hoping to do it myself. Thanks again, and if you have any questions about what the hell I was trying to explain, let me know. Thank you and have a great day!

 
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After reading #1 I understand that you radiator fan was not being turned on. Whether it's the ecm/pcm not communicating, temp sens not communicating, some open path in fan motor circuit, or just a faulty motor. Your description nails that dead on.

If there was only drips present when you took coolant temp sens out, that would indicate a problem. So there should have been a little bit more that came out, maybe that's what you meant just a small amount came out? This is because you sensor is placed on a path coolant travels, so if it was full there would be more than just drips.

After reading #3 I don't know what the problem is but I can make some general statements that may help.
-When car bogs it normally indicates lack of fuel or lack of air.
-When your car first turns on your PCM uses fuel tables that Honda engineers come up with as an avg fuel ratio needed to run the car (normally on rich side). When your O2 sensors warm up your car switches to live fuel tables reflecting O2 sensor readings.

With that said, one probable cause would be way off fuel demands or low fuel demands or what ever the case may be. It's possible your air/fuel ratio is really off (cause it seems like when car switches to live fuel tables it corrects itself). Now why it's really off, or is that even a problem is a good question haha.

And don't dismiss the head gasket, it may not necessarily be coolant going into you oil, there's a few different flavors of head gasket failures. Ill list below
-water jacket to cyl
-water jack to oil gal
-oil gal to water jack
-oil gal to cyl
-cyl to cyl
-or any of those could also push out externally (making it visible under the hood)
Also if coolant and oil do mix whether its in cooling system or lubrication system it will appear to be a milky like substance.

My advice: From reading your posts I'd say this isn't something you probably want to take on by yourself. Find a local, reputable, independent Honda/Acura, or import shop and take it there. Describe in detail symptoms in detail to service writer, and ask for a quote on diagnosis and tell them not to take anything apart without them contacting you (which if there reputable they should do this anyways).
It sounds like advanced engine performance issue. I have no further help to offer without actually touching the car lol. Hope that helps good luck

P.S. And if you do decide to take it to a shop let me know and Ill break you down a short and simple list of symptoms to tell service writer; cause if it gets to lengthy they may just be dismissive and say "we'll let the technician figure it out".

 
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Oh and I also understand you said your fan was turning on, but is it possible you could of been hearing a/c fan, or blower motor and thought it was radiator fan? cause it really sounds like fan was not engaging in city driving.

 
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Thanks again for the info. I'm pretty positive it's the cooling fan, I know it's not the a/c fan because I make sure never to run it (the car is stressed out enough), and I'm not sure what the "blower motor" is. The fan turns on when the needle rises at stop lights and turns off when I start to drive.

Also, when I said "drip" I actually meant "poured" out. It wasn't a gush but it definitely had some pressure to it and I had to refill my radiator when I was done replacing the CT sensor.

As far as the head gasket, wouldn't there be a persistent problem that I would notice...not just a lag the first 5 minutes after I start it up?

This fuel table you're talking about, and how it is somehow off, seems to me the best assumption to what is wrong. Just to make sure, my engine isn't a V-Tech so non-V-Tech engines have this also, right?

If I put fuel injector cleaner in it there isn't a long term side effect to that is there? I know with radiator leak stop you are just kind of covering up the little problems that are a symptom of a bigger problem.

Anyways, thanks for all the help, I appreciate it!