Engine hunting

[Quadcob]

When I first start the motor the motor dosn't idle well, it hunts up and down for about 10 - 15 seconds before it smooths out. Once the engine warms up it still idles fast. I have checked for air leaks, but there dosn't appear to be any.

Any suggestions

Warren

 

[Lextreme II]

Are you running stock ecu or aftermarket ecu. Do you have larger injectors or fuel pump. If everything is stock, its most likely would be the ISC. However, if you have aftermarket fuel system and ecu, its most likely its running rich and its a tuning issue.

 

[Quadcob]

The motor is from a crown running every thing stock. As the vehicle is manual it only uses the engine ECU.
The throttle body was replaced with one from a Soarer because it has only one butterfly.

Warren

 

[doey]

This may or may not help.
http://planetsoarer.com/IAC/iac.htm

Thanks Peter.

 

[Lextreme II]

From my personal experience. Replacing the bearings on IAC or ISC doesn't really help that much. Most of the time its not the bearing problem. The best thing to do is to test the ohms of the ISC. You can also unassemble the ISC and do some cleaning.

 

[Peewee]

After you've checked the ISCV/IAC, and verified its working fine, recheck for air leaks.

Air leaks are usually the cause of high idle and hunting.

 

[Quadcob]

The problem that I had has(I think) been solved.
When I replaced the throttle body I decided not to run the water from the rear of the motor through throttle body to the ICV.
This was the only thing that was not standard so this afternoon I installed the hoses to complete the water circuit.
Started the motor and although it idled vey fast there was no hunting. I stop and started the motor a couple of times and now the it starts and idles smoothly around 800rpm.
Now the only question is why did the water circulating through the throttle body and ICV fix the problem(icing up of the ICV causeing it to be sticky)?

Thanks everyone who had an input into the problem

Warren

 

[bansheebuzz]

What vehicle is it in and who did the wiring? from experiance it will be in the wiring. Mine did the same thing until i had time to finish of a few other connections to the ecu. Now it start and idles perfect from cold

 

[jibbby]

Bouncing idle - look into these...

Dirty or irregular working throttle body
Vacume leak
Throttle Position Sensor
O2 sensors
ECU

 

[Quadcob]

bansheebuzz and jibbby,
The car is a Cobra replica and I wired it myself. Checked the wiring and it was OK and with the exception of the O2 sensors everything was checked.

When I did the last posting I thought I had overcome the problem, but when I started the car again it had all of the original symtoms, back to drawing board.

To cut a long story short the problems turned out to be:-
Hunting- Once I had the motor wired I started it. When I turned off the motor I would isolate the battery as I was still wiring the rest of the car. Every time I would start the car I would turn on the isolator switch and when I was finished I would isolate the battery.
This proceedure would reset the ECU and when I started the motor the ECU would go through its repower process.
Once I relised this and left the power turned on the hunting stopped.

Fast idle- Adjusted the throttle cable, fixed. So simple.

As you can see both problems self inflicted and althugh it had me stumped for a while they were both so easy to fix.


Warren

 

[dar_sbb]

Hey guys

i have a very similar issue to this. It doesnt hunt all the time though. It idles very high though... at around 1500 - 1700rpm... and it normally hunts when im coming to a stop and clutch in. It will hunt for a couple of seconds and then stop... but will continue to idle high.

If i bypass the ISC... all is fine.... just struggles to start when cold.

The funny thing is that it was working fine, then i went off road and it started to happen. So im not sure if its the wiring or just a faulty ISC. Im going to pull the ISC out 2nite and give it a clean to see if it will do anything.

its in a hilux Surf... and only o2 sensor codes come up.