Throttle position sensor
 

Hi All,

MY99 Classic UK turbo version 5 with EJ205 engine.

Having a bit of bother with high & lumpy idle. When I start the car from cold the revs will shoot up to about 1800 rpm & immediately drop to a lumpy idle hunting between 1350 to 1450 rpm. When the car is up to temperature the idle rpm will increase slightly & idle lumpy between 1450 to 1550 rpm.

After say a few miles driving I will stop at a junction, when I disengage the clutch plate at standstill the revs will shoot up to about 2100 rpm dropping back over about 5 or 6 seconds to 1650 to 1750 rpm & hunt between that higher ranges as long as I stay still. Am also getting a bit of jerkiness on light throttle in every gear, haven’t even got to high throttle yet as am still running engine in after complete rebuild.

What would be the sort of factory spec if you like in regards to the voltage range between the throttle plate in the fully closed position through to the fully open position? I back probed mine & currently have 0.76 volts in the FCP & 4.53 volts in the FOP. The sensor works as it should increasing & decreasing in the proper manner as I rotate the throttle plate. Was just wondering if this was within factory spec for a uk turbo as I have read on forums that others have been getting 0.45 to 4.60 volts but they were discussing an STI. I don’t know if it’s the same for an STI as it is for a turbo? There is a bit of difference in the FCP reading of 0.76 so was just thinking that if this was indeed to be high then it would be telling the ecu to idle higher through the signal wire. Didn’t want to remove the sensor just yet as hear they can be a bit fiddly to set back up. Also please refer to the list of work below I have done to date to try & rectify these issues, if you have any other suggestions believe you me they will be more than welcome!!!!!!!:brickwall

I have cleaned tested & then changed the ICV, cleaned then checked the throttle plate for correct position, checked throttle cable not too tight, installed new maf sensor, new pressure sensor, new 02 lambda sensor, new turbo intake pipe, new OEM inlet manifold gaskets & torqued down to 25 nm, new magnecor ht leads, plugs have only 12 k & are gapped properly, checked all pipework & vac lines off manifold. Checked all fuel pipework from the tank to the injectors with car running. Then I got access to the same car as mine that was running well 5 minutes prior & changed over the air box pipes through to turbo intake pipe, changed out the intercooler, Y pipe & dump valve, changed the boost solenoid & associated hoses, the pressure exchange solenoid & associated hoses, changed over ecu & checked grounds. The problem still persists!!!! I have an inlet manifold PCV valve in the post.



Any feedback would be much appreciated. Cheers Paul.

Sounds like you have gone through the logical steps replacing likely parts that could cause this.

Have you tried a new coil pack?

Thanks for your response cutmaster.

Getting access to the same car as mine again over the weekend hopefully so am going to swap over the coil. This might rectify my jerkiness under light throttle.

Cheers Paul.

The voltage is ment to be between like .46 and .48 at closed throttle (iirc), if yours is backed off and reading .76 I would say the sensor is faulty. Usually icv causes most problems but you've cleaned that so Id go back to that sensor. Ecu has no reason to adjust the position sensor - that sensor tells the ecu how open it is to relate to fuel etc, well you probably know this lol.

My Bug Sti went through the same rigmarole just recently, finally sorted when I took off the fuel filter and muck and water dribbled out. A new one installed and the car was back to normal. Might be worth trying after all your efforts,

Thanks for your reply MH.


Job is now a good one:luxhello:


Yes it was the throttle position sensor.


I think what has happened is I have had my engine in & out 3 times in the last 2 months & the last time I put it back in I think I must have knocked the sensor when I was refitting the intercooler & intercooler Y pipe onto the turbo discharge nipple. This had moved the potentiometer slightly in turn increasing the voltage that was being sent down the ECU signal wire.


When I back probed the TPS I had 0.76 volts with a fully closed throttle plate. When I rotated it to fully open I had a reading of 4.53 volts.


Loosened the screws & moved it until I had a reading of 0.483 volts with a fully closed throttle plate, buttoned it up & the job was a good one :thumb:


Cheers Paul.

Thanks for the reply Paben.


As per my last post it was the TPS being moved slightly that was the problem.


Cheers Paul.