OK, I have been working on cars for 45 years now and this issue with my Altima is driving me crazy. When the vehicle is cold and you place it in reverse the throttle sticks and engine races. I have to either back in to a parking spot (once the engine is warm of course) or quickly shift it to N. I am not sure what the issue is but it is driving me nuts(in reverse) . Once the engine is warm and has been driven for awhile it seems to be fine. Very dangerous indeed !!!, I have checked the throttle cable for binding and it seems to be A-OK
The problem might be with the Idle Air Control valve.
The IAC valve is what controls the idle speed depending on the load put on the engine. So if the transmission is put into gear, the IAC valve bumps the idle speed up to compensate for the load so the engine doesn’t stall. Or if you turn the AC on, the IAC valve bumps the idle speed up from the load imposed on the engine from the compressor preventing the engine from stalling.
IAC valves can be effected by temperature. They act up when cold or when they get hot.
Idle speed increases when you shift into reverse? Hey, that’s a new one. I have a similar vintage Corolla, and had a problem with the idle speed being too high, did some research and found on my car anyway the idle speed is designed by Toyota to increase under several conditions
- Engine coolant is cold
- Steering wheel is turned
- A/C is turned on
- Headlights are turned on
So first off, make sure when you engage reverse, you also aren’t doing one of those too as part of your routine. It wouldn’t be unusual to accidentally turn the steering wheel slightly for example when engaging reverse.
It’s possible on your car the idle is supposed to increase when the transmission is engaged in reverse, but for some reason it isn’t working correctly. On my Corolla the way the idle speed is increased when you turn the steering wheel for example, is there’s an air valve in the power steering pump that opens when the power steering pressure increases, and this allows extra air to flow into the intake manifold, which is the same from the point of view of the engine as if the throttle was opened more, increasing the idle speed. There may be some similar air valve in your automatic transmission that opens in reverse, only it is opening more than it should. If this is how it works on your car, and you could find the air hose from the transmission to the intake manifold, and temporarily block it off, then if the high idle problem went away, you’d know at least that was the source of the trouble.
As a DIY’er, that’s my basic method of figuring out high idle problems caused by designed-in drivability functionality. Temporarily block off auxiliary air paths into the intake manifold until one of them makes the problem go away.
Other possibilities include a clogged throttle body, and a malfunctioning PCV. But I have no explanation why those would only affect reverse. That’s a puzzler.
You might gain some perspective on this by reading through the thread posted a few months ago, where I had a high idle problem. The experts here offered up many good ideas to help me solve it.
Edit: I forgot to mention, make sure to take advantage of the built in diagnostic software provided by your car’s manufacturer. Read out those diagnostic trouble codes from the computer’s memory. That’s the first thing to look at.