Model: 97 Civic HX, CVT Transmission (Problem Solved - Not, see posts below)

This winter the enginestarted to have an RPM fluctuation (approx +-100 rpm, 1 surge/sec) when driving at low engine speeds (1.5 to 3 thou rpm) and low throttle settings until getting all the way warmed up, then it mostly runs smooth. Check engine light - OFF, eng codes read: 00.

Correction: Just test drove again. It also surges slightly after warmed up to full tempwith throttle around 1/4 to 1/3 open.

Could this be a problem with the IACV (Idle Air Control Valve)? It idles good though. Starting to think this not the problema.
Also, thinking of checking out the TPS (Throttle pos. sensor). Am I on the right track?


Thanks for any suggestions.

 

First try cleaning the IACV and then bleeding the coolant system of possible air bubbles. Another thing to look into is whether you have a vacuum/air intake leak.

 

RonJ,

I took off the radiator cap, plumb full so I don't think that's the problem. I'll try cleaning the IACV later today.

Thanks,
Phil

I took your advice and bled the coolant system.Thanks for thediagram below. Boy that was fun! Got covered in coolant when I finally got the block drain bolt out. I drained out about a pint or so out of there and on to me. I don't know if I had any air inthe system and still don't know if I do or not, but I'm done with this step for now.

Which sensor or deviceis it that could cause the engine surge from an air bubble in the coolant? The IACV?

 

Just cause it's full doesn't mean it's been bled properly. :]

 

+1

 

U B right Timmy my man, UB right!

 

RonJ You Are The Man!

Igot the air bubbles out of the cooling system and now it runs perfecto!

I honestly didn't thinkthis was the problem because the last time I worked on this car was back in August 07 (its Feb 08now) when I put a new Timing Belt on this engine. I thought surely any air would be out of the system by now! But, then again, this car has not been driven much since then (my daughter got her license suspended so the car has just been sitting).So I figured what the heck, I'lltry the coolant bleed deal to see what happens. That did the trick, she runs like new! (I assume the air bubbles were messing with the IACV).

For those who might try this: I let her cool, removed the radiator cap and turned the Heater Control Lever inside the carto full hot (red and to the right). Start engine: As the engine warmed up to operating temp and began circulating,I noticed air bubbles (Yes! air bubbles) coming up to the top of the radiator filler hole opening.Air must have been left in the heater core after the above Timing Belt job. After a couple minutes this stopped. I think I could have stopped herewith the Air Bleed procedure accomplished butI went ahead and drained some out of the engine block drain bolt (just above and ahead of the oil filter) which was a pain in the azz and I think probably unnecessary. Remember after the bubbles stop, top off the radiator with coolant, put the cap back on and fill your overflow reservoir with coolant so when the engine cools it will suck coolant back into the radiator keeping it full with no air.

Good luck to anyone else with this Engine RPM Surge When Drivingsymptom.

A Confession: The surging came back again the next day, but not as bad. Also, after it warmed up all the way it started to run fine. This is now officially an intermittent symptom. I guess I'll be checking/cleaning the IACV to see if that helps or maybe its a bad ECT. I'll repost here if I get it figured out.

 

Yeah, Mxs said that if bubbles get trapped in the IACV or the ECT within the thermostat housing, then the ECU gets discombobulated, throwing off the idle.

 

No, not fixed I'm afraid. Still doin it. Replaced the O2 sensor. I'll look for intake air leaks and clean the IACV next.