What would cause an 88 Honda CRX to rev up and down while sitting still and no one pushing on gas pedal?

Answer 1

Answer In my case just by installing a new head gasket was enought bucause if air is seeping it will reflect with that diagnose

There is an air leak somewhere between the throttle plate and the intake valves. What's happening is this: your car is designed to run on a perfect "stoichiometric" ratio of air to fuel. IIRC it's 14.5 parts air to one part fuel. If more air gets in than is supposed to, your O2 sensor will see the mixture getting lean and start adding fuel to compensate--which, of course, makes the car run faster. Eventually, your fuel injection computer will look at the RPM the engine's running at, look at the throttle position, decide there's no damn way an engine with a closed throttle should be turning 2800rpm, and cut off the fuel to slow the engine back down...and the cycle begins again. Idle hunting actually tells us two things: air's getting in where it's not supposed to, and your induction system is working fine other than that because if it wasn't, you'd just lean out the engine until it self-destructed. Now understand, there are a lot of good suggestions in this thread...but when you do one of them, you'll also go around with your screwdriver and tighten all the screws in the system, which is what fixes the problem. (Besides, you need a new O2 sensor anyway. Replacing it saves gas, and you've seen the price of it lately.)

Be aware that these leaks can be tricky--I've seen leaky fuel injector seals do it. But start with the U-shaped pipe that runs from the air cleaner box to the throttle body--especially the clamp at the bottom that's impossible to get to.

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Vaccumm line leaking

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i have owned a crx for two years and the one thing i did to fix a jumpy idle was change out my O2 sensor (located before the cat). when you add exaust (headers included) to a car the O2 sensor reads different than it is supposed to, it also gets dirty much faster.

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This can be related to an item called the EACV, a tubular unit mounted on the back of the inlet plenum, by the throttle body. There are two water hoses and a multiplug going into it. It is held onto the plenum by two bolts.

Undo the multiplug and the two bolts and you should be able to pull the EACV sufficiently far away from the plenum to be able to clean it out with some carb cleaner. Make sure you don't lose the figure of eight O-ring that seals the unit to the plenum. Bolt it back on and plug it back in.

Hopefully that should solve the problem.

Chris

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The MAP Sensor. Mass Air Flow Sensor sounds like your not getting enough air causing it to idle up and down. I had the same problem on my Accord.

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The most common solution to an unstable idle (particularly cold) on a crx is the throttle cable is adjusted to tightly. I know it sounds bogus but it used to happen all the time on the crx's due to the cable's insulation getting old & hard.

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i have an 86 si with same problem. I adjusted the idle to specs and adjusted timing and prob went away. The correct timing at idle is a must.

The person referring to the EACV is most likely correct. It's actually a wax throttle control. Over time the may become to sticky and get stuck open. Had it been an O2 sensor, you would experience other driving issues: slow take-off, surges @ cruise speeds and so forth.

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is a unit call Idle air control valve, i race my crx with a jdm 1.6 dohc vtec, and most Honda have that unit located behind the intake manifold. the radiator fluid run thu it. if u follow a very small like 3/8 size hose is back there.

clamp down both hose so u won't lose any coolant.

take both hose off, unplug wire harness

then take the unit off, u see a rubber gasket take that off.

use carb cleaner spray both port. let it sit for a min then dump out the cleaner, then

use air spray inside then spray it with carb cleaner again, until u see a white color plastic and everything look clean.

use little bit of gasket sealant around the gasket, place the sensor back on. let the sealnt dry up. i would wait about an hour. plug everything back in.

then it should fix the problem, but if it doesn't then replace the unit, its almost a 200 unit. so its not cheap.

and other thing too, make sure u have no air bubble and also not low on coolant.

now its fix! and there's nothing do with your o2. u can also able to lift the floor up by passenger side front, and u see a metal plate bolt to the floor, the ecu its right there

and see any code coming on, it should be a flasher red led light thu a sight glass.

code 14 its iacv. flash 1 long, 4 short.

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Another strong possibility is that your coolant is low. Low coolant screws with the temperature sensor, which in turn screws with the ECU. The ECU, seeing an alternating hot/cold condition, responds accordingly by flipping the engine back and forth between hot and cold loop. As cold-loop requires more fuel (because it's assuming that the engine is cold, and therefore needs to run rich until it warms up), the car revs as the mixture richens and then leans out.