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2001 civic idle problem


I have replaced a head gasket on my 2001 civic LX recently. I have drain the coolant and put it back on again. Now I have idle issues, the car starts fine with high RPM (because it is cold) about 5 min latter the RPM changes, it revs low and high (about 2000 rpm) when it should be idling normal. I have taken the radiator cap (before i start the engine) and run it a while with the cap off to purge any air pockets, no luck. Another thing I have realized that there is a pressure build up in the upper and lower radiator hoses when it is running with the radiator cap on.

Any ideas on how to fix this problem?

Isn’t it normal for pressure to build up as the engine heats up and the water expands? I would think the radiator cap releases some of the pressure if it builds up too high. What’s the water temperature gauge say?

You will need to go back over your work, and check that you did not miss reinstalling a vacuum hose or plugging in something. Be sure also that a small vacuum line bit not get pinched between the head and block…or any other areas.


temperature gauge reads normal. when i open the radiator cap before I start the engine I see lost of coolant.

If you are losing coolant I’d think that the head gaskets did not seat or something was not done right.

Did you torque the head bolts and were they torqued dry as they should be. Also, some head bolts are not reusable as they are stretched at the original torquing (when the car was new) and cannot be reused.

Coolant may be leaking into the cylinders. You most likely put new plugs in so there may not be any signs if you pull the plugs.
If you have availability of a bore scope I would try the following.

Start the engine and leave it get to operating temp. Shut the engine off and let it cool for an hour. During this time the pressure in the cooling system should push coolant into at least one cylinder if there is a leak… Then pull the plugs and take a look with the borescope. You should see at least a little coolant accumulating on the top of the piston.

Also check that the oil is not getting a milky look. This would mean that coolant is leaking into the crankcase.


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Do you mean “loss” or “lots” of coolant? If it is loss of coolant it’s quite possible that you didn’t top it off sufficiently after you put the heads back on. I would make sure the coolant is topped off, the reservoir full and then start the engine and observe the engine and what comes out the tail pipe. Water in the cylinder should produce some white smoke.

I just re-check the air connections, to my surprise I have forget to connect an air hose, that has been fixed. Thanks to your help. Now I have a poor idling problem. It starts and runs normal, till I give a little gas. Once I give a little gas the RPM raises and drops way too low, almost dies, but it recovers and there is an unusual shaking (not too much but it does not seem normal) on engine. So, now what it might be?

I would re-check again and when you are done re-checking I would do it one more time…to make sure all hoses and vacuum lines are connected properly. The spark plugs are properly seated and connected and if that does not help, I would re-check again.

@matteous, Please tell me more about your head gasket work. Did you send the head to a machine shop to have it planed? Was it warped? How much was it warped?

Is your “check engine” light on? Have you pulled the codes?

Idle problem somewhat fixed but still running rough. Now I did scan the codes, there are bunch. Codes P0113, P0301, P0108. Check engine light is flashing. Well, where do I start?

Ohh, for got to mention that when i pull the spark plugs, #1 spark plug look wet and smell like fuel. That is the only spark plug looked wet

Check the large diameter vacuum hose from the intake manifold to the MAP sensor. It may be leaking air at one of the connections, or has cracked & split. What I’d do for that is disconnect it at the intake manifold, and use a hand-held vacuum pump to check that it held vacuum all the way to and including the MAP sensor.

You have a misfire on cylinder #1, check for spark and compression (I assume the spark plug is wet with fuel).

The MAP and intake air temperature faults sometimes occur on vehicles like this because owners and volunteers unplug sensors while the engine is running to see what happens next. I erase the faults and see which ones return.

BTW the large diameter vacuum hose goes to the brake booster, not the MAP sensor.

On my Corolla anyway, there’s two large diameter hoses connecting to the intake manifold. One goes to the MAP sensor, and the other to the brake booster. Could be different on a Civic though.

I’ve left the MAP sensor disconnected accidentally, and indeed it turns on the CEL light straight away on the Corolla.