I recently bought a second-hand 2003 Honda Odyssey that had been very well-maintained. It had just had its belts changed about 6 months ago, too. After taking ownership I noticed a slight hissing sound when running the A/C. I didn’t think much of it. Months later(today), I drove to work with no problems. But when I got into the car in the afternoon, I noticed the van was revving erratically. Not very high, but maybe up one full tick and then fall off. This was worrisome. Later when I got home I noticed the TSC light had come on as well. Anyone have an idea on this one as well as the general cost of repair? Thanks!
This could be something as simple as a disconnected or cracked vacuum hose.
When a vacuum hose is defective, the most common symptom is idle speed that rises & falls in a somewhat rhythmic pattern. And, because the engine is not running at its optimum when there is a vacuum problem, the ECM turns off features like the TCS and the Cruise Control.
What puzzles me however, is that you didn’t mention whether the Check Engine Light is lit up.
Usually when the TCS is disabled, the CEL is also lit up.
@VDCdriver, on either of my vehicles, if the TCS is disabled (or if you pull the fuse), the MIL will not come on–I guess they figure the TCS and ABS lights are enough warning. I don’t own a Honda though, so I can’t speak for whether that system behaves identically. Other than that, I totally agree with you.
For the “hissing” A/C, a system that is undercharged will sometimes make this sound. Does the A/C cool normally? A very slight hissing sound may also be completely normal for your vehicle. It may just be the sound of refrigerant flowing through the system. On some vehicles it’s more noticeable than others.
Does the revving occur all the time, or only at a cold start or when the van is warmed up? Does it only occur with the A/C on or all the time?
The hissing has been there since I purchased the van a few months ago. We don’t regularly use it, maybe once a week, but I do recall always hearing the sound coming from the air conditioner and wondering what it was. I figured it was perhaps normal and not a problem. Yesterday I went on a short 3 mile or so trip. On return I stopped somewhere and got out of my van. When I was getting back in I heard the engine revving up and a tick and then falling off, revving up, falling off. I drove a bit and it didn’t seem to be much different while driving. I had another stop to make on the way home and after getting back in the van, it did seem a little off while driving. As I parallel parked I noticed that the TSC light had come on as well as one of the other lights. It was either engine or transmission(I can’t remember off the top of my head, but can check on that)…
I don’t know the specifics of the Odyssey HVAC control system. But by the description, I’ll assume that many of the HVAC functions are vacuum controlled (which is common). A broken, cracked, disconnected, etc. vacuum control line would explain the hiss and the wonky idle. (I.e. vacuum leaks hiss and make for funny idle). I’d start by stuffing my head up under the dash behind the glove box.
I can’t think of a connection between that and the TCS. Maybe there is one, or maybe it’s just a different thing altogether. But the best place to start is having the system scanned for error codes - which should be present if that light is on.
I checked the van again and, yes, the Engine light and the TCS light were on.
^
…as I suspected you would find…
Now, you need to find out what trouble code(s) have been stored by the OBD system.
Once you get the codes read (free-of-charge at Auto Zone, Advance Auto, O’Reilly, or–possibly–Napa), come back to this thread to post them. They will be in a format similar to “P0123”.
Does this symptom change at all when the brakes are applied vs not applied? A vacuum leak in the brake booster diaphragm is a not uncommon problem, and can cause this symptom.
I actually have an appointment with a mechanic in the morning to check it out. He said he needed to check the codes first. Just hoping I won’t be bleeding money this time tomorrow 
Ask your mechanic for the codes detected, post them, and the experts here may be able to help interpret what they mean.
So sorry for the very late response. It turns out it was the Idle Control Valve. Set me back $435 or so here in Hawaii. Van is running fine now. Funny side story(not funny). I have a 1998 Honda Odyssey that I was hoping to sell, but needed to replace the belts and fix the brake light. Well, I went to start it and guess what? Yup, it had the same exact problem. So I just pumped $700 into that one for repairs. Ouch!
Glad you got it fixed and back on the road! That’s the amazing thing about cars, it is pretty much impossible for an ordinary person to break them so badly they can’t be fixed, and for a price that is fairly affordable (although always too much). Not so true of your DVD. When the DVD player breaks, you can pretty much know in advance it won’t be possible to be fixed.
Many thanks for the update.