I have a question that my service manual does not seem to address.

I have an 86 TA with carb and manual trans. When I initially start the car, it idles properly at around 750, nice and smooth. When the car is still cold, you can burp the throttle and it returns to the proper idle.

When the car warms up (just above 100 degrees, probably around 120 or so), when you burp the throttle it will rev up to around 2000 RPM and will just hold there. The only way to get the idle back down is to shut the car off and start it again.

Because the idle holds steady, it clearly isn't a vacuum leak. It seems that there may be a sensor that is reading incorrectly when the car warms up and the computer takes over controlling the idle speed.

If anyone has any suggestions as possibilities to check, it'd be greatly appreciated.

I should also add, this carb is a freshly rebuilt unit from National Carburetors.

Thanks in advance.

 

i know of nothing that would bring it up to a steady 2000rpm only to be reset by a restart

thats bloody strange. theres not a dodgy cruise control vacuum cylinder or something on this thing is there?

is the throttle cable moving freely?

 

The car does have cruise, but currently the cable that goes to the vacuum canister from the carb is unhooked (I have to acquire one of the cable clips at the local auto parts store).

The throttle moves free and when we had it running over this past weekend, the only part on the carb that didn't return to the normal "base" position after bumping the throttle was the accelerator pump.

I am assuming it isn't a vacuum leak only because the idle is right around the correct 750 when first started (and will actually return to the correct idle speed until the car begins to warm up as previously stated).

What I may try next time I have a chance (and I may have already but don't remember) is unhooking both the IAC and MCS on the carb to see if they are playing a part in the high idle. If those aren't having an effect, then I guess the next appropriate course of action would probably be to remove all emissions lines from the carb and plug them all to make sure I don't have a solenoid or vacuum port that is opening when the car begins to warm that is causing an inadvertent vacuum leak.

Though, I would tend to think if it was vacuum related the throttle wouldn't have to be bumped for the idle to go high...