Babber

Hi folks,

Hoping you could help a guy who's knowledge of mechanics is limited. I have a 1989 Prelude (B20A3 engine - dual side carbs) and it idles terribly high. I'll list some of the symptoms:

1) At start-up it revs to about 2500 rpms and stays there unless I let it warm-up for about 15 minutes.
2) Changing gears - when I put in the clutch to change gears the rpm's go UP.
3) When I come to a red light and need to stop and either have the clutch in or put it in neutral, the rpm's go UP.
4) Dramatically reduced my gas mileage (I'm getting about 200 km's less per tank).

I have my ideas but with my limited knowledge thought I would ask here first. Could it be the thermostat? Choke? Idle screws?

Thanks for any feedback or suggestions.

Babber

Colfax

It sounds like you have a vacuum leak. If you didn't mess with the idle screws or choke adjustment, I would leave them alone. They don't usually go out of adjustment on their own. In fact, I wouldn't touch any of the adjustments on those carbs unless you know what you're doing. It's very easy to mess them up, and then you'll never get them right again.

Check for vacuum leaks before you do anything else.

__________________
89 Prelude 2.0Si 4WS
91 Prelude Si - SOLD

Babber

Thanks Colfax.....I've read in other posts that the EGR valve could be the culprit...would this be considered a vaccuum leak?

Colfax

I'm not sure what you would see on the carbie lude if the egr valve goes out. But I'm pretty sure you would have a vacuum leak if the diaphram in the egr breaks and is the cause of the failure.

__________________
89 Prelude 2.0Si 4WS
91 Prelude Si - SOLD

Babber

Thanks Colfax....much appreciated.

mean89

Ever find out what exactly your problem was? Mine does the same thing, doesn't idle quite as high, but the symptoms sound the same. When I stop at a red light it starts off at the normal low idle and gradually goes up

Babber

Hi. Yes I did find out what it was. I had the thermostat replaced and adjusted the high-idle screw (a little) and problem solved.

It actually kind of ticked me off though because I suggested to two other mechanics it was the thermostat and they disagreed. Finally found a guy who was familiar with carbs and he diagnosed the problem straight away. I had him do the work but it's pretty easy if you want to do it yourself. Replacement thermostats are inexpensive too. I should have just done it myself when I thought that's what it was.

You can find instructions on how to replace thermostat online.

Hope this helps.

Babber

Colfax

Makes perfect sense now, lol. So it must have been staying open all the time not allowing the engine to warm up sufficiently to turn off the choke then. The fuel economy part should have steered me towards the t-stat but I've seen so many vacuum problems with these things I jumped there with both feet.

You had it diagnosed in your first post. You ought to trust yourself more and go with what you are seeing on your end because in the end, you're better able to see what's going on than we are.

Glad you got it fixed and it didn't cost you too much. I'd say you should keep in touch with this tech and pick his brain whenever you have problems. They're usually willing to help you out if you occasionally give them some work.

__________________
89 Prelude 2.0Si 4WS
91 Prelude Si - SOLD