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My car has always had a sporadic bouncy idle when cold every since I got it back running. Depending on just how cold it is, it might bounce upon starting it up from dead cold, it might not. Sometimes it would stop bouncing even before it got up to running temperature. Just yesterday I noticed my radiator was leaking all over the top seam, so I replaced it. I made sure to follow the proper bleeding procedure (per Eric’s dirrections) at the thermo nipple first upon filling the radiator, then let it get up to operating temp to kick on the fans. I’ve done this twice to no avail. The idle just keeps bouncing.
I’ve also done a smoke test on the intake and sprayed carb cleaner all around the intake to observe any changes and nothing. Unplugging the IACV results in the bouncing stopping, but the idle drops to 1250 and chugs there. My timing gun indicates it is staying at a rock solid 1250, no fluctuation, but you can clearly hear it chugging. Screwing in the idle screw all the way on the throttle body affects no change. So obviously I can’t set a base idle. If I take the cap off of the FITV and cover it with my hand, there is no change. Pushing down on the plunger will make the engine rev higher.
This erratic idle, while present before I replaced my radiator, it was infrequent and I could work around it easily. But replacing my radiator has really made it bad. It makes me think I haven’t bled the radiator of all the air, but what gives? I’ve done everything by the book, or so I think. What might I check next? I have the Honda Service Manual but it’s hard to get a clear direction.
Summary: ’91 Accord bouncy idle that has become undriveable after radiator replacement. No coolant leaks. No intake leaks. New FITV, IACV. Smoke test negative. Coolant bleed procedure has been done twice. Engine has never overheated during the time I’ve had the car. No CELs.
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Ok so I know me updating this so soon will make it seem as if I really haven’t been working on it, but after rereading the Accord specific forums I ran across a little detail of how the FITV works. There are two holes in the throat of the throttle body on the left hand side. The top one is where the FITV receives air. Blocking this off effectively cancels out the FITV (you can feel the suction with your finger while the engine is running). I started the motor, blocked it off with my finger, and the idle magically returned to its normal warmup speed of about 1100-1200RPM. After letting go, it STAYED THERE. Is is possible some air worked its way into the FITV and had a hard time getting out?
I’m currently letting it get up to operating temp.
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