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Old 13 Jan 2013, 06:41 am
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Default 98 honda prelude idle on start up?

I have a 98 honda prelude sh and when I start it it revs to about 2k which i would say is normal to warm up but then the rpm will fluctuate going down to normal then jumping to 2k over and over until it warms up it does it more when it is cold outside. Any ideas on what it might be? Also what is the best way to clean carbon out of an engine. I know engines lose power over time because of all the build up i just wanna get rid of some of it to return some of those lost horses. I took the egr off and cleaned it with carb cleaner, anything i can do other then the other stripping it down and rebuilding. Thanks.

its a 5 speed and the oil is all good and it has no problem charging anything never had any other problem with the alternator. i heard somewhere it could be the map sensor but im not sure. no cel is thrown
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Old 13 Jan 2013, 06:46 am
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It could be a few things. One thing I can think of is your alternator is going bad... Or your engine motor oil could be low... Or your transmission (but that's over thinking it). Check your alternator.
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Old 13 Jan 2013, 07:01 am
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Join Date: Sep 2007
Posts: 234

The first thing I would do is run a couple of tanks of chevron super unleaded through the gas tank and for the first tankful go buy a can of techron from the auto parts store. this is a really good fuel system cleaner in its own right and by the end of the first tank the vehicle should be running better. I don't know what the rpm issue is off hand but if its because of being gummed up the chevron will help and put the techron in right at the gas pump then pump it full and take it for a several hour drive if possible and help break up and loosen any deposits that may accumulate over time.

Buy keeping the engine running it will help burn off any deposits from crappy fuel which is usually the problem with carbon and fouling and other build up GAS especially low budget gas does not have the cleaner burning chemicals in it that the car needs. And over time becomes worse and worse. cleaner gas has better fuel and is a lot better for your car.
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Old 13 Jan 2013, 07:17 am
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Join Date: Aug 2009
Posts: 400

Idle hunting is a favorite Honda hobby. It can be miserable to track down, but the place to start is to make sure there is not a bubble in the cooling system driving the Fast Idle Thermo Valve crazy. When the engine is cold, open the coolant purge nipple (on top of the upper radiator hose housing at the engine, if I recall right) half a turn until a steady stream of coolant comes out. Since yours settles down when it warms up I doubt that is the problem but it is a place to start. The next step is intake cleaning, which you can combine with your decarboning. Seafoam is popular but I am not a fan; it leaves an oily film behind that requires using it over and over every few months, like heroin. The way it is sucked into the intake sometimes causes engine damage, too, especially in Honda engines. Dodge dealers sell Mopar Combustion Chamber Cleaner for about $6 per spray can - it is easier, safer, and more effective with no addiction. (Sounds like an ad for a new prescription medicine!) Anyway, you use it according to the directions in the first source. My son used it in his Acura after a year or two of fiddling with Seafoam and it worked better and he no longer has to keep retreating it.

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