93HondaCivicDX

I have searched all through this site and have yet to find an answer that addresses my particular issue. I have a 1993 Honda Civic DX, 1.5L 16 Valve, 5 speed with about 180K miles. My radiator had a crack in it and when the coolant level got low it would start revving up and down when I was idling. There has been no problems when I was driving. But the second I put it in neutral the engine starts revving up and down. Prior to replacing the radiator, I could simply add more coolant and the problem would go away. Now I have replaced the radiator, fuel filter, cleaned the IACV (Idle Air Control Valve), changed wires, plugs, distributor cap, air filter, complete oil change, and PCV valve, yet still have this problem. The coolant level is full. When I unplug the IACV, the revving up and down stops, but then it becomes more of a short and rapid revving up. Not near the fluctuation as when it is plugged in, but still not right. When I unplug the TPS (Throttle Positioning Sensor) the engine revs jack way up and stay there until I plug it back in. The first time I unplugged the MAP sensor the car idled perfectly and did not shut off. I plugged it back in and then unplugged again and the car cut off. I have been told it is supposed to shut off when the MAP sensor is not plugged in, but wanted to give as much info as possible. There is no CEL (Check Engine Light) on until I unplug any of the above. I also have sprayed Brake Cleaner on the vacuum lines as I was told this was a way to find a leak, but did not notice the engine respond any differently than it did prior to the spraying. My car was cold when I did this, not sure if that matters. Any help would be most appreciated.

z6hatchboy

I noticed your "cracked radiator" try bleeding your coolant system. It may have air in it.

93HondaCivicDX

I just bled out the coolant and refilled it. I did stay out there for over 30 minutes after I filled it with the cap off and every time air bubbles came up and lowered the coolant level, I topped it off. It still revs up and down. Just to be clear, I had the car off and took out the drain plug at the bottom of the radiator. Took off the cap and allowed it to drain completely. Then started the car and watched the temp gauge. Allowed it to go up until normal operating temp and then shut the car off. Did not notice any additional coolant draining. That is when I put the plug back in and filled it back up. Thanks for the advice, z6hatchboy. Any other ideas what might be causing this?

pimpinblackcivic

airlocked iacv

93HondaCivicDX

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by pimpinblackcivic &raquo;</TD></TR><TR><TD CLASS="quote">airlocked iacv</TD></TR></TABLE>

I don't understand what that means. Since I have already taken the IACV off and cleaned it, I assume that won't fix it being airlocked. What would? Do I need to buy a new one? They cost $195 from AutoZone which is why I tried cleaning it.

93HondaCivicDX

Can anyone tell me what an airlocked iacv exactly is and how would I fix it? Do I have to buy a new one or is there a way to clean it other then the thread that is about cleaning out the ports with Brake Cleaner. I've already done that. Thanks for all the help on this thread as well as all the threads out there. Just signed up here but used quite a few things off here before.

Unit44justin

did you try replacing your t stat?

packman5280

idle lfuctuating can be an intake manifold leak. just a thought.

93HondaCivicDX

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Unit44justin &raquo;</TD></TR><TR><TD CLASS="quote">did you try replacing your t stat?</TD></TR></TABLE>

No I haven't tried replacing my thermostat since it appears to be functioning properly. I haven't experienced anything out of the ordinary in regards to temperature. What makes you think the thermostat would contribute to the idle fluctuating only when the car idles?

93HondaCivicDX

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by packman5280 &raquo;</TD></TR><TR><TD CLASS="quote">idle lfuctuating can be an intake manifold leak. just a thought.</TD></TR></TABLE>

Is there a relatively easy way to find out if the intake is leaking? Thanks for the thought. All are welcome.

blk92_d16

Carb cleaner around possible leaks might clear up the idle and show you where the leak might be.

93HondaCivicDX

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blk92_d16 &raquo;</TD></TR><TR><TD CLASS="quote">Carb cleaner around possible leaks might clear up the idle and show you where the leak might be.</TD></TR></TABLE>

Do you mean on the vacuum hoses? I tried this once with Brake Cleaner as opposed to Carb Cleaner but the car was cold. Basically I started it up and started spraying. I didn't notice any difference in the idle or anything else. Should I allow the car to warm up and use Carb Cleaner instead? Thanks for the help! It's greatly appreciated.

rasinhell

had this same problem just 2 days ago. cleaned out the iacv, didn't work. so a friend had an extra laying around and I paid him 50 bux to replace it. problem solved.

93HondaCivicDX

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rasinhell &raquo;</TD></TR><TR><TD CLASS="quote">had this same problem just 2 days ago. cleaned out the iacv, didn't work. so a friend had an extra laying around and I paid him 50 bux to replace it. problem solved.</TD></TR></TABLE>

Thanks for the tip. I was under the impression if I cleaned it out and that didn't work it must be some other part. I'm sure I can find one at a junk yard with low miles on it. Mine has 180K and just now went out. Much better then the $195 from the store. I'll try that and let you know what happens. Thanks rasinhell!

93HondaCivicDX

Definitely not the IACV. I bought a new one and installed it, but still have the same issue. Anyone got any other ideas???

93HondaCivicDX

I guess no one has any other ideas. Thanks for the help from those that tried.

Former User

I think you may still have air bubbles in your cooling system because you didn't bleed it properly. Here's the recommended procedure:

(Start at step 7)

93HondaCivicDX

Thanks for the diagram. You are correct when I posted that about draining my system I didn't do it properly. I did talk to a guy this weekend who told me about the bleeder screw. Saturday, I let the car warm up to normal operating temp and cracked the bleeder screw. Immediately antifreeze streamed out with no air bubbles and I locked it back down. I waited about a minute and then repeated that process about 5 times. None of the times did any air escape. Now I am going to replace the thermostat since I had a post on here telling me that might be the issue as well as another guy telling me that. Granted no one has been able to tell me why they think that is the problem. But it is only costing me $33 total to do this and with 178,XXX miles on it it couldn't hurt. I'll repost tonight after it's done and let you all know the results. Maybe it will help someone else later down the road. Thanks again.

Former User

As mentioned by you and others above, it might be worth retesting for an intake air/vacuum leak by spraying carburetor cleaner around the hoses/lines and intake manifold when the engine is warm. Note that the best time to do this procedure would be when the engine is having the idle problem. If you have a leak, the engine should bog down.

D50boy

That radiator leak didn't cause you to overheat did it? One extreme is that you may have warped something (valve or head) when it got hot. Just a thought.

A compression test and a leakdown test would tell you for sure.

93HondaCivicDX

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RonJ@HT &raquo;</TD></TR><TR><TD CLASS="quote">As mentioned by you and others above, it might be worth retesting for an intake air/vacuum leak by spraying carburetor cleaner around the hoses/lines and intake manifold when the engine is warm. Note that the best time to do this procedure would be when the engine is having the idle problem. If you have a leak, the engine should bog down.</TD></TR></TABLE>

I am going to try this in just a minute after I install the new thermostat. I used Brake Cleaner last time but the engine was cool. I will do it this time when the engine is at normal operating temp. But I have been told it's best to use Starter Fluid. Would you agree?


Modified by 93HondaCivicDX at 3:27 PM 3/6/2008

93HondaCivicDX

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by D50boy &raquo;</TD></TR><TR><TD CLASS="quote">That radiator leak didn't cause you to overheat did it? One extreme is that you may have warped something (valve or head) when it got hot. Just a thought.

A compression test and a leakdown test would tell you for sure.</TD></TR></TABLE>

No I never overheated when the radiator was cracked. The closest I came was one night I was driving and I saw the temp gauge start climbing quickly. I turned the heat on full blast and pulled over immediately. The gauge never reached the top mark. I cut the engine off and allowed it to cool down. Since there was a crack in the radiator to begin with there wasn't a great amount of pressure built up. I took off the rad cap after a few minutes and let it fully cool down. Once it had I filled it back up and proceeded home. The temp gauge was at normal level the entire drive home.

Where could I get a compression test or a leakdown test? I honestly don't know anything about either.


Modified by 93HondaCivicDX at 3:28 PM 3/6/2008

D50boy

Any service shop can do those tests.

93HondaCivicDX

It's not the thermostat. I just replaced that and bled out the system according to the diagram supplied. The engine still revs up and down when idling. I have not tried to spray Starter Fluid on it yet as I am having it washed right now. To be clear though, anytime the car idles it revs up and down. Whether at a stop light after driving, sitting in my driveway, etc. Even when I turn the car on from a cold start, it revs high until the car reaches it's proper temp, then it starts revving up and down while idling. Once I start depressing the accelerator it goes away. Granted if it is relatively cold I can put it in 1st or 2nd gear and apply no gas, the car will move itself and once it gets to the point where it would cut off it gives itself enough to keep going at a higher idle. After a small amount of time, say 10 seconds, it will go back down and run until it almost cuts off. Then it will repeat this process. Hopefully that last part makes sense to you all.

I will post again after I get a chance to spray the vacuum lines and around the intake manifold.

Dasfinc

yea, that REALLY sounds like a Vac leak.