Technical Idle problem

[lee89]

Bit lost on this one really, spent all weekend trying to figure out why it wont idle properly. When cold it revs up and idles at 3500rpm when warm it idles keeps reving itself between 1000-2000 rpm. It squirts fuel in at 1000 then stops, revs itself as its leaning out then squirts more fuel in at 2000 so the revs drop back to 1000 then the cycle continues.
Its had a new coolant temp switch a few months back and this weekend a new idle control valve, throttle potentiometer, air temp sensor, map sensor, lambda sensor, crank sensor. I even got a complete throttle body from scrap yard just as a test and still no change.
There are no air leaks, vacuum gauge reads normal and still goes ok.
Ive tried disconnecting the battery and leaving it off over night, ive tried the supposed ecu reset procedure in haynes manual and still nothing, ive checked all the sensors and im running out of ideas now.

The only way it seems to sort of idle normally is when the map sensor is unpluged and the injector light comes on and goes into default mode.

Any one got any ideas?

 

[rallycinq]

What happens if the throttle cable is disconnected?

Cheers

D

 

[lee89]

Makes no difference. Next stage i think is to get it plugged in and have a look at live data from the sensors etc

 

[rallycinq]

MPi?

Cheers

D

 

[lee89]

Spi

 

[fingers99]

Remove the nipple on the throttle cable, check the hose to the map, ensure that there's plently of slack on the throttle cable. Remove the TB and clean it with plenty of pound shop carb cleaner. Last step, compression test.

 

[lee89]

Map piping all good, throttle cables slack, throttle body's spotlessly clean, and compressions all good across all 4 cylinders.

 

[fingers99]

IAC, If not and no inlet air leaks, I give up.

 

[rallycinq]

I'm still fairly convinced its a vacuum problem.

Cheers

D

 

[lee89]

Took the tb off again earlier, made 2 new gaskets up for the spacer just to be double sure i can rule that out. blanked off the servo hose and the connections on the back of the tb including the purge valve one for the evap control, also the one for my vacuum gauge just to make sure no air could get in/out and also replaced the inlet mani gasket as well and still exactly the same symptoms.

Only way it will run is with the map sensor unpluged so the ecu goes into default and puts the light on then it injects fuel in a steady stream not just a big dolop at a time.