Replaced Water Pump,
Join Date: Aug 2009
Location: New Zealand
Lean running at around 2000 RPM
I've just replaced the lambda on my 98 156 2.0 TS manual, as it had given up the ghost and gas consumption was crapola. Unidiag and FiatEcuScan both reported a constant voltage indicative of a non-functioning lambda and open loop situation.
After replacing the lambda, I did an ECU and throttle reset via Unidiaga using 0xFE via the In Out Crtl Ll 30, followed by the 90 sec on off warm up routine. Huge difference!!
After a day of driving a hesitation/sluggish/ developed at just under 2000 rpm. After reading various threads on here on AO, I removed the throttle body and cleaned this with carby cleaner, removed and cleaned the valve at the end of the breather that connects to the plenum behind the throttle body (ECV?). I also stretched the spring a wee bit. Checked the tube from MAF to TB for leaks and none detected.
I removed the TSP unit -I'm not keen to disassemble the TPS/stepper (by the way this is a CF2) as I understand the TPS pot in these is a sealed unit- and reassembling I noticed that it held the butterfly open a little. Is this normal? I assumed that the stepper was holding the butterfly a little open in the 'start' position and once started would then dropped back from this position as the stepper motor eases it butterfly almost closed to reduce the idle speed. The tps unit allows the spindle to rotate freely from this slightly open position. The stepper/idle control effectively determining the position of the closing 'stop' for the butterfly.
This cleaning made no difference. So I attached Unidiag and realtime graphed lambda voltage output. This oscillated normally until the hesitation occurred during which the lambda indicated a lean signal. I understand that the lambda isn't causing this but recording the lean mixture.
I checked for errors and got:
"DTC: P0170 Fuel Trim Malfunction (Bank 1)"
"State S.C. to Ground /Below bottom limit, Present and stored. Not Requested"
Selecting "Idle Status" in the Realtime Select yielded this message:
"Idle recognition test Performed
Throttle minimum opening Out of Limits
Idle recognition signals Not Synchronised"
I also noticed that after a drive into work the and stopping in the carpark the lambda signal stopped ocillating and went to high steady voltage indicating a rich mix.
Also the temp dial indiated around 80°C normal driving and climbs to an indicated 90° if left idling. Temp rises quickly and is stready. FiatEcuScan displays these temps as 88°C and 98°C respectively, so I'm not sure which to trust. The lean condition can occur hot or cold.
I have a couple theories.
One, the TPS unit is the culprit that is our of limit in some way, indicated by the slightly open butterfly. The error messages seem to support this. I read in one thread about holding the butterfly shut while rotating the TSP into position, although this seems like forcing against the stepper and its gears, which I'm a bit nervous about. The TPS itself appears to gererate an accurate line when graphed in unidiag.
The MAF is misreading the airflow into the engine, but there is no evidence of this and it seems to graph normally.
Anybody has anything similar, your advice/ideas would be appreciated.
Darryl in New Zealand
Last edited by KiwiAlfa156; 01-10-10 at 03:04.