89 Prelude Idling very rough

Great, 2 posts about the same car. BTW, the car is a 1989 Honda
Prelude S (2.0 SOHC)

This problem relates to it's idling. When the car is first started,
and the choke is engaged, there is not problem. When at highway
speeds, no problem.

When the car is warm, and out of gear (at a light, or clutch is in, or
coasting, or etc.), she idles at approx 500-700 RPMs.

I've checked the idle screw. If I make it idle above this
level(1000RPMs +), the car will diesel when turned off (continue to
run for 10-15 seconds.

I've checked the readout of the diagnostics built into the car. The
readout gives me a "two" (two pulses followed by a long pause). This
readout, when looked up in the repair manual, says the problem is with
the Vehicle Speed Sensor.

This problem started happening about the same time as when the
speedometer stopped working.

I've called several Honda Dealerships, asking for pricing on this
Vehicle Speed Sensor. The dealers claim that there is not one on my
car.

I'm bringing her in to the dealer to be hooked up to the computer for
a good reading. Is this going to be a waste of my time and money?

W

 

Appears to me to be a good plan. The computer you mentioned in the last
paragraph should be able to identify the problem.

 

As there is possible a sensor attached to the speedo cable, would
suggest that the computer is getting false readings nad getting mixed
up. Try replacing that first....You can correct me on this but it seems
possible with computers.

 

Jon,

I "received" a copy of the Service manual online (thanks, emule), and
found that the speed sensor IS on the back of the dash. The speedo
cable not working was in fact, as you (and I) guessed, the reason for
the really bad idling.

I had the speedo cable replaced a couple of days ago, with the
following results:
- better idle
- more engine power (better fuel mix, i guess)
- no more engine light
- I know exactly how fast I'm going. I had a rough idea before,
but this is nicer.

Thanks, everyone.