I have a 91 CRX hf and am having problems with the engine running erratically. I start the engine and warm it up and then after it has been running for about 5 minutes the RPM's will bounce up and down. The problem is that it doesnt do it all the time and I dont know what I should do about it. Any help would be great.

 

Have you had a tune up on it lately? Have the car lost power lately and the ECU reset? Do you have any codes flashing on the ECU?

 

The valve lash probably should be set again but I wouldnt think this would cause the engine to run rough and even if it did, it should do it all the time. A long time ago, about a year and a half ago, the check engine light came on but I brought it to a shop and I think it was just a sensor. I remember somebody said if the coolant wasnt full some sensor on the throttle wouldnt let the computer control it and would cause an eratic idle. I didnt quite understand that coolant had anything to do with how the throttle is adjusted but who knows. I did try filling the coolant anyways becuase it needed a little but this still did not fix the problem. The coolant should be replaced anyways so I need to do that.

 

I have the same exact problem going on right now as well. The problem is only when i'm sitting at idle after the car has warmed up a bit.

From what i've read on other threads, it has to do with the EACV (controls idle via ECU) located on the back of the intake manifold (tubular shaped sensor with two bolts and a two wire plug connecting to the drive side of the sensor).

***I recommend the following to see if it fixes your problem***
So far i've:

-Thouroughly cleaned EACV, and tested resistance across two connector pins (within tolerance)
-Cleaned entire throttle body
-Cleaned EGR assembly (I was getting a computer code 17, i believe? Translated to EGR Valve)
-Replaced all vacummn lines anyway associated with idle (Fuel pressure regulator, PCV, MAP sensor...)
-Replaced PCV
-Checked Grounds (Regrounded EVERYTHING under the hood)

The part that you mentioned about the coolant having something to do with the sensor is true...if there are any bubbles in your coolant, the flow of coolant may not flow smoothly through your warming plate for your throttle body and into and out of the EACV sensor. This prevents the sensor from accurately detecting when it's time to begin regulating with warm-idle conditions. I've also read that there are mechanical sensors that regulate cold-idle, but i'm not too sure where they are on my car, or if they exist at all (I have an 89 CRX HF).

Anyway, after re-assembling everything I checked out, I ran my car with the radiator cap off until the thermostat opened up (to remove bubbles from the system), then I waited for the car to rise to normal operating temperature (cooling fan started to cycle). I then unplugged the connector from the EACV (Car idle dropped) and I used a straight slot screwdrive to adjust the idle screw to within tolerance (650+- 50). Idle screw is recessed and somewhat hard to located at first (located on the top left of the throttle body looking into the intake manifold from the passanger side).

Idle was set, EACV was plugged in, car ran fine for a week

Now it's happening all over again. No computer codes, no check engine...Car surges (not like a vacummn leak), but more like the idle is hunting from 1000-1500rpms when the car is warmed up. It's not incredibly annoying, but it is noticeable, and i would like it to stop. The only other thing that I can possibly think of is the Alternator might be going, and the demand on the alternator is fluctuating. However, I already hit the battery terminals with a voltmeter and got a solid 14.4volts when the car is running...

I'm stumped.

But it's not that big of a deal because I got a swap on the way soon (d16z6).


Modified by SexwithaRex at 1:42 PM 3/14/2006