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1999 Honda Civic with manual transmission stalls when changing gears

I have a 1999 Honda Civic DX hatchback with a 5-gear manual transmission that I have been driving since the day it left the dealership. This morning, on my way to work, I was shifting from third gear to fourth gear and the car stalled. This has happened three times in the last month or so. I recently had my transmission fluid flushed. I’m 95 percent sure this started after the transmission fluid was flushed. Any ideas as to what might be wrong?

Thanks in advance!

We need a little more info.

Why was the xmission fluid changed in the first place? Routine maintenance, or because you had a problem they were trying to address? Are there any unusual noises since the xmission fluid was flushed? Grinding? Growling? Does the acceleration seem sluggish? Any difficulty shifting from one gear to the next, up or down? When starting out from a dead stop, do you notice it is more difficult to get the clutch to engage smoothly? Any check-engine lights or MIL’s?

There aren’t that many things that can go wrong with a xmission fluid change. I guess they could forget to refill it, or forget to put the drain plug back in. Or they could have put the wrong fluid on the refill. Filled it too much or not enough. But an experienced mechanic generally wouldn’t make this kind of mistake as the procedure generally isn’t any more complicated than an oil change.

Having the manual transmission fluid changed won’t cause the engine to stall when shifting. I would look more towards a problem with the Idle Air Control valve.

The IAC valve is what controls the engine idle speed anytime the throttle is released and the throttle plate closes. So when you go to shift gears, and let off the accelerator, and step on the clutch pedal, the IAC valve is what allows the engine to continue the idle.

Sometimes the IAC valve can stick from gum. varnish, and carbon where it fails to go to the proper position for the idle condition and the engine stalls. You can try removing the IAC valve from the throttle body and clean it along with idle air bleed port on the throtlle body to see if that fixes the problem. Otherwise, the IAC valve may be defective and requires replacement.

Tester

Tester --If it were the IAC, wouldn’t this show up as a rough idle or very low idle rpm when the car was just sitting at a stop light? Or does the IAC operate differently during a brief throttle down? I wouldn’t have guessed the IAC b/c it only occurs at higher speeds, 3rd to 4th gear. You’d think an IAC problem would be more obvious sitting at a stop light after the engine had warmed up.

Not nesessarily. The clutch pedal not only has an inter-lock switch that prevents the engine from starting unless the clutch pedal is depressed, but it also has a switch that informs the computer when the clutch pedal is depressed at speed. The IAC valve has to respond faster under this condition because the accelerator is released and reapplied in a very short period of time. So a sticky IAC valve could cause this problem.

Tester

Ok, thanks, I learned something new about how the IAC operates in newer cars. My early 90’s Corolla only has one clutch interlock switch, and it only is used to prevent in-gear starting. I don’t think the IAC knows anything about shifting or not shifting. The IAC is only for keeping the car idle smooth when stopped at a stoplight I think in my car; i.e. the ECU has no knowledge of the clutch interlock. But, ok, I understand now that the newer cars have a second clutch switch switch used for keeping the idle speed within limits when shifting.

After the car stalls, does it start right back up or do you have to wait any amount of time before it will re-start? You could also have a fuel pump on it’s way out. When was the fuel filter replaced last?

Thanks for the responses! Here are answers to your questions:

Why was the xmission fluid changed in the first place? Routine maintenance

Are there any unusual noises since the xmission fluid was flushed? No, none. The car runs great otherwise.

Does the acceleration seem sluggish? No. Acceleration feels normal.

Any difficulty shifting from one gear to the next, up or down? No

When starting out from a dead stop, do you notice it is more difficult to get the clutch to engage smoothly? No. Clutch engagement feels normal at all times.

Any check-engine lights or MIL’s? No

Thanks again!

I think Tester is on the right track. This is unlikely to be related to the xmission flush, unless perhaps a wire was inadvertantly dislocated in the process. That seems unlikely, so at this point the IAC is the prime suspect.