Hello everyone,

This is my first post. I have a 96 Honda Civic EX with almost 400K Kms. About 3 weeks ago, I changed the spark plugs, rotor, cap, engine wires, fuel filter, and recently MAP sensor, and checked Ignition coil, the Idle Air Control Valve. There is no CEL on, no soft or hard codes in the PCM/ECU and the Honda techs suspected the MAP sensor.

My problem:

When I start the car, and let it "warm up" for 2-3 mins, the idle would drop slowly as per normal and sometimes, when it's just above 1500 rpms, it would jump up to 2000 rpms for a second or two and then slowly start it's decent down again normally. Once it is under 1000 rpms, it would sometimes drop to almost 500 rpms for 5-6 seconds, the car would shake and almost stall but recovers 100% of the time. When I drive the car within the first 20-25 mins, this lowering of the rmps would occur and I would lose power with the car. I have to pump the gas peddle to increase the rpms to keep the car moving during this time with little power. Once the 5-6 seconds are up, the power would return. After the 20-25 mins on the road, it stops doing this but idles rough. Highway driving is out of the question because during this time, the car chokes and shakes very bad to try to get speed above 80 Km/hr.

I still want to keep this car for a few more years, can anyone suggest what might be wrong with this car so that I may fix it or get it fixed?

Cheers,

The_Fly

 

First check whether the engine timing is out of spec and whether the timing belt has slipped a tooth or two.

If the timing and timing belt are fine, then check the fuel pressure. You might have a faulty fuel pump or pressure regulator.

Regarding the idle problem, you also might want to bleed the cooling system of possible air bubbles and check for an intake air or vacuum leak.

 

Hi RonJ,

Thanks for the reponse. The timing and belt were checked and all are good. I just had the fuel pump replaced last year and was told by Honda that if it was the fuel pump, the car wouldn't start or wouldn't stay on.

How do I safely check for a vacuum leak. I've heard of using starter fluid spray and other flammable aerosols that would cause the engine to increase the idle rpms when it was sprayed on or near the leak. That isn't very safe. The other option would be to have a smoke machine check it I guess. I have tried very very soapy water and looked for bubbles but I did not find any leaks.

What is the best way to check the pressure regulator given that I have just the Joe Public tools.

Thanks,

The_Fly

 

The fuel pump or fuel pump wiring could be intermittently or partially faulty. You should test the fuel pressure with a fuel pressure gauge (picture 1). You may be able to rent one at an auto parts store like AutoZone.

Yeah, starter or carburetor fluid is the way to go, though I do understand your concern about the fire hazard. The soapy water method won't work because, if you have an intake air or vacuum leak, soap bubbles would be produced internally and therefore would not be visible to you.

Again, you need a fuel pressure gauge (picture 2).

 

Hi RonJ,

Thanks for this info. I will update when I have all these things done. Hopefully it's something simple and inexpensive.

Cheers,

The_Fly

 

Hey RonJ,

I have now checked the TPS and that is fine as well as the Idle Airflow Control Valve. I was also told to check the Egine Coolant Temperature (ECT) Sensor. I have tried this by measuring the resistance between the 2 pins as per Haynes manual but when it's cold I get 188 ohms (0.2 Kohms) and when it's hot I can't get a reading. According to reference values, when cold at 32 degrees Faraheit, it should be at 5Kohms and when hot at about 0.2 Kohms. I thought that this was the problem and got a new ECT, but before I put that in, I measured the resistance and got no reading on the new one. I put that new one in boiling hot water for 5 mins in a shallow bowl and then tried to read the resistance and once again I got no reading...this is driving me nutz! Next is the Fuel pressure and vacuum checks for the fuel pump and the pressure regulator.

I am also noticing that this idling problem happens whether the the engine is hot or cold but more so when it is cold and during frequent stop and start trips.

Thanks,

The_Fly