3500RPM at idle , help

[Guest putputcar]

hi all, my 93 supra was acting up last night. After I put the gear in "Park", my idle shoots up to 3000rpm. When it's in gear, it's at 1400-1800rpm.

 

I haven't really done or change anything to the car recently, the most recent change was an auto transmission swap.

 

I read for a bit earlier and seems like there IS NOT a screw where I can adjust the idle like other cars??

 

thanks for your help in advance.

[Ian C]

Is it a MAF or MAP based car? If it's MAP based you may have an air leak after the throttle body.

 

You may also have a stuck idle control valve - does it rev to 3000 then fall again back to about 2000, and cycles like that regularly?

 

-Ian

[Guest putputcar]

I have a VPC. I noticed it cycles up and down a bit but more like 3200rpm- 3500rpm though.

[Ian C]

If it cycles regularly then it's probably getting too much air in but it's metering for it. The VPC is like a MAP I think? If it measures the air pressure in the plenum post-throttle butterfly, then it'll fuel correctly for any air leaks, such as leaving a hose off the plenum or the idle control valve sticking open.

 

Check the ICV - make sure it's moving. You can pop the hose off it and hold up a mirror to watch the plunger come in and out.

 

If it isn't moving, it could be stuck (use brake cleaner or a solvent in it) or the signals aren't reaching it, or the stepper motor is bust. If it is, you've got a big leak elsewhere in the system, although I'm not sure where you'd get one big enough for that effect - I know leaving the PAS takeoff hose off only raises the idle to about 1,100rpm

 

The revving up and down is a safety feature in the ECU - if it detects runaway revs with no throttle input or engine speed, it cuts fuel to drop the revs again - hence the oscillation.

 

-Ian

[Guest putputcar]

I unplugged and plugged back a bunch of connectors around the intake manifolds, it's now dropped back to

 

at "P" and "N", 1400rpm -1600rpm

In gear, 1000rpm.

 

then later, I cleaned the ICV valve, it's still the same as nothing change.

 

at "P" and "N", 1400rpm -1600rpm

In gear, 1000rpm.

 

I did unplug the ICV connector while the car is idling, the car shows no reaction to it. is that normal?

 

is it same if I adjust the TPS a bit? I'm thinking just loosen the TPS bolts a bit, tap it counter clockwise (if that's the direction to lower the throttle position reading).

 

 

thanks in advance.

Edited October 19, 2008 by putputcar (see edit history)