Not sure whether this is the place but I will give it a go.

My 94 TS has been running great of late. I put a new head on after I blew a water hose and cooked the old girl putting a nice canyon between the seats and blowing the head gasket. All fixed now. Last week I noticed that my idle was all over the place. Started really low (500 rpm) then it has shot up to 1900 rpm. Now it is stuck there. It also hunts, jumping from 1800-1900rpm quite quickly.

Done the usual, replacing the Vacum hoses and checking for leaks but still no luck. This has not affected the performance that I can tell but I don't drive my car that hard.

Today I noticed that while driving along in 2nd with revs up at 3500rpm or more and back off, as you de-accelerate, the car wants to drop back to normal idle speed. When the revs drop to about 1000rpm's the engine wants to accelerate up to 1800-1900rpms again. Is this a vacum affected problem?

Where would be the best place to start. I have disconnected the Air Volume Sensor and also the ISC to see if this makes any difference and it makes very little. I always thought the Air Volume Sensor was critical for the running of the engine and the car would not run with it disconnected.

Thanks for any help in advance.

there is an idle speed screw near the throttle body....u could try dialing it in a little bit, but for it to behave so weird...i dunno, maybe the screw is missing....also try cleaning your Throttle body out.
Im not sure was gonna say ISC but guess not.......
We need Killbilly in ere.

Disconnect your battery, leave it an hour or 2 then reconnect and idle for 20 or so minutes.
Also reset your base idle, there are 2 pins to short, if you look at the tech section of Madmagna there are pics there, if the problem persists I wold look towards either a vac leak or a faulty ISC.

The other thing is of you have had the TB off make sure the gasket is not back to front as this creates a Vac leak.

my 2 cents, check out your fuel pressure regulator, maybe the heat of the car overheating caused it to die?

We need Killbilly in ere.

lol Madmagna's covering my back ;)

Do the ecu reset, like what madmagna said...and then check it again.

Also a quick check to see if your ISC is faulty is to turn the aircon on, if the idle doesnt rise, then chances are your ISC is stuffed.

The symptoms you describe are a little different to what normally happens with a faulty ISC though, there is the possibility of an electrical problem there too.

Instead of leaving it two hours simply stand on the brake pedal. Discharges anything left in the system to an inductive load i.e the light bulb.

Thanks for your help,

I did the reset of the ecu and it did not seem to fix the problem. Was told by a freind to try the Mass Volume sensor. Disconnected that and the car still runs. Problems still there. MVS stuffed? Is that normal behaviour?

Next step, Clean the throttle body. Process of elimination.

I have an aftermarket Oxygen Sensor where I was required to cut and join the wire. Could that be casuing this problem. When I installed it, the car was going fine. I know those things run on resistance.

Killbilly,

:(

Would be a good test of the ISC if I had Air Con. Something I noticed, if you disconnect the ISC, the hunting stops. However the High idle speed is still maintained.

Do you have a multimeter?

I'll see if I can dig up the test you do with a multimeter to check if the unit is faulty.

It sounds electrical to me, but Im not an auto electrician and Im no mechanic either lol. Madmagna has much more experience with this than I do


EDIT:
Found the page:
http://www.nardek.com.au/testisc510-10.htm

Mal, maybe you'd like to put this address in the Tech Torque FAQ sticky?

If you want to check the airflow sensor, just hook up a test light to the diagnostic connector to check for error codes - takes the guess work out. Check out www.madmagna.com for the pins (I think it's 1 & 12 from memory) and codes. If your sensor was shot your idle would be very erratic and run very rich (bad fuel consumption).

hey this might be whats wrong with mine aswell. my idle has also been acting very strangely plus ive well documented my fuel consumption problems. where is the isc?

For testing ISCs, look at this:
http://www.dsm.org/how-tos/tttt/tttt3.html

Your ISC is on the throttle body, should be a six wire connector.

Mine was crap, but I got another one, but it also helped when I got the temperature up a bit with the right thermostat, but I don't think this is your problem.