DillonInCO

I've posted about something similar before (RPMs hanging when I put the car in neutral) but never found the problem. Now it's gotten worse. My car has a regular throttle surge at all RPMs, as if I'm blipping the throttle when I'm not. Yes, that's right---it's not just at idle, it does it even if I'm on the gas, and it's causing accidental acceleration if I'm not careful. As an example, in a parking lot in 1st gear, get off the gas and every 3-5 seconds it will start taking off, then drop back down to where it should be.

What could cause this? First thought would be vacuum leak, but there's no check engine light, and it still pulls just as hard as ever. I'm guessing it's electrical. Can someone link to any writeups about the throttle sensors and wheel speed sensors on our cars? I am also interested how to adjust the set screw on the throttle body. I've had an aftermarket TB for a long time, and this is a new issue, but it couldn't hurt to check.

Soldier GT

What mods do you have?

ticopowell

Have you cleaned the TB lately? I know sometimes cars have issues idling with a dirty TB, not sure if it would affect cars at more than idle...
Hope that helps, it's all I can think of.

DillonInCO

Only mods I have are CAI, TB (I think 70 mm) / upper plenum, and canned 93 octane SCT tune. And I did clean the TB when I installed it, yeah. Anyway I found the reason I've never noticed this before: it only happens when the HVAC switch is in the "mix" mode. Never used that before. It doesn't do it at all otherwise. How on earth is that possible?

dhavi4226

If your HVAC is selected to any A/C or Defrost position you should check to see if the A/C is actually working. Had the same thing (fluctuating idle) with my 97 saleen. turned out to be the A/C cycle switch and recharge. Not a terribly expensive fix.

DillonInCO

The "mix" position doesn't use A/C, does it? Anyway, I haven't had to use A/C in a few months, but it blew ice cold back then, and didn't affect RPMs more than A/C normally does. And it's not just the idle that fluctuates. I can get off the gas with the car in gear and in motion (i.e. it should decelerate), and every few seconds, the RPMs will raise and the car will accelerate slightly, as if I'm giving it a bit of gas. Something must be causing the throttle cable itself to move? Unless there is some other way that the ECU could read the throttle as if I were on the gas when I'm not?