Failed mot for emissions and when u start the car up whether cold or warm,it revs up and back down continously.please help smells like its running rich,drives ok and all but at idle the revs keep going up to about 2500 rpm and back down
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you really should have your vehicle testing done in a main station like the rest of europe and not done in a back street back hander type place ,its you own fault for not taking a mecvhanic with you to the auction ,right been given my orders by the boss so have to go now answer this post and i look at mail this evening
You don't say what state you are in and what the requirements. The early 90s Honda Civics frequently are high on emissions under certain circumstances depending on how the test is run. If you are in a state that allows you to get a waiver with a certain amount of repair - that would be the recommended way to go. A lot of times the amount required is enough to detect the problem, but if not it is basically the cost of keeping the car. I am in Washington State and my 91 Honda Civic runs great and gets 38 mpg but fails the test. I have a new O2 sensor, catalytic converter and distributor and fail. I pay $150 for repairs / waiver every 2 years - and I am an ASE Certified Master Tech. I figure $75 a year saves me a car payment.
I had the same problem in my 97 civic dx. Once the car warmed up it would rev up and down whenever the car was idling over and over again. To fix it I found out that the spring on the throttle body was sticky and by spraying it with lubricant (WD-40 or something similar) and working it into the spring until could stretch and contract freely, I never had the problem again.
It is running rich. Verify the readings are within specs from the O2 sensors, they should fluctuate up and down once the car is hot, constant high reading is rich run, very low is lean or defective sensors, also clean the throttle body and air-bypass valve, changing the oil can help as well. Do you have any OBD 1 Codes in the system memory?