Volvo Owners Club Forum - View Single Post - 2001 V40 1.8Gdi starting & idling issues, won't rev

theboymike · May 30th, 2019, 13:15

Right, got this sorted and wanted to post the bare bones of how it was achieved in the hope it might help others in a similar situation in future!

After keeping an eye on ebay for a while (and getting let down by the absymal comms of one useless seller) I managed to score a used (but apparently previously refurbed) throttle body assy from Gata958 (Alex) who I believe is resident on here as gatos.

From the off Alex couldn't have been more helpful; making me aware of the need to allow the ECU to recalibrate itself to the new parts and taking the time to talk me through possible remedies to the issues I was having - thanks Alex - I'm foreven endebted to you for all you time and advice

So, the new throttle body was fitted to the car with the old throttle position sensor as I'd struggled to remove its electrical connector when removing the old TB. Unbeknown to me at the time the TPS' mounting bolts holes are slotted to allow some rotation of the unit relative to the TB.. in the absence of any better info I fitted my old TPS to the new TB so that the plug was at approx 6 O'clock when view from the passenger side wing of the car.

Next I tried setting up the ECU using this method, however this achieved very little (other than wasting a load of time a fuel) as the car wouldn't idle at less than about 1400rev/min, which would randomly spike to around 2k

Alex suggested rotating the TPS with respect to the TB in an effort to offset this issue; and while I thought I'd won (as the adjustment was clearly making a difference to idle speed when carried out while the engine was running) as soon as I drove the car the idle was back up to where it was.

As a disclaimer, in retrospect I might not have carried out the ECU calibration procedure above to the letter (I didn't turn the ignition to "Lock" only position 2) so the failure of this to work might be on me..

Anyway, suspecting an issue with the TPS position I attempted to quantify the resistance across its terminals as per this diagram:

Long story marginally less long I don't think that these values above are correct for the TPS on my car (perhaps they're for the earlier cable-operated throttle on the pre-facelift cars, which I believe has a different TPS..?).

Setting the TPS to give 2.5k Ohms across pins 1&4 when fully closed meant the TPS was noticeably offset clockwise by maybe 5 degrees, and also meant that at fully open the reading across pins 3&4 was something like 0.75k Ohms.

In addition to this I found that when fully closed the resistance across pins 1&4 was infinite (not the 2.5k Ohms stated), as it was when fully open across pins 3&4.

Evidently this needed a bit more investigation so I cobbled my own TB back together with the TPS from the replacement unit and set about poking it with the multimeter in the comfort of my own home in an effort to validate the results I'd had from the unit on the car.

After again setting the TPS to get a reading of around 0.5k Ohms across pins 1&4 with the TB closed gave a value of around 0.76k Ohms across pins 3&4 with it wide open. As with the unit on the car this setting saw the TPS displaced clockwise from the 6 O'clock position.

I split the difference between the two readings at around 0.625K Ohms in each case and fiddled with the TPS position to achieve this -ending up with a reading of 0.623k Ohms on pins 1&4 with the throttle closed and 0.622k Ohms across pins 3&4 with it wide open; positioning the TB exactly at the 6 O'clock position as I'd found it on each TB before disassembly.

Bear with me, we're getting to the end! I also found that across pins 1&4 from fully closed, as the throttle was opened the resistance value rose from 0.623k Ohms to a peak of 2k Ohms at around 50% throttle opening, before going to infinity beyond this point. In addition I found that across pins 3&4 from fully open, as the throttle was closed the resistance value rose from 0.622k Ohms to a peak of 2k Ohms at around 50% throttle opening, before again going to infinity.

So.. in summary it appears when "centralised" the resistance across pins 1&4 measures the throttle position from closed to half open (its value increasing as the throttle becomes more open), after which point the resistance across pins 3&4 takes over (its value decreasing as the throttle opens further).

I also found that, unlike as stated in the diagram above, the resistance across pins 2&3 isn't constant / irrespective of throttle position - it changed very much like that of pins 1&4 did over a similar range of values.

Armed with this knowledge / the confidence that both TPS units are working correctly I attacked the car this morning. I got the plug off the TPS by removing the unit from the TB and hooking a pick under the steel retaining wire then pulling it off completely (making sure it didn't fly!). You might also have luck in prizing the end of the wire away from the plug at its ends on each side to allow the plug to with withdrawn one side at a time.. I didn't have a flat-bladed screwdriver small enough to try this, though.

(Continued below as the forum seems to be imposing some weird word limit..)

May 30th, 2019, 13:15	#8
theboymike Junior Member Last Online: May 23rd, 2022 19:06 Join Date: Apr 2011 Location: Oxford	Right, got this sorted and wanted to post the bare bones of how it was achieved in the hope it might help others in a similar situation in future! After keeping an eye on ebay for a while (and getting let down by the absymal comms of one useless seller) I managed to score a used (but apparently previously refurbed) throttle body assy from Gata958 (Alex) who I believe is resident on here as gatos. From the off Alex couldn't have been more helpful; making me aware of the need to allow the ECU to recalibrate itself to the new parts and taking the time to talk me through possible remedies to the issues I was having - thanks Alex - I'm foreven endebted to you for all you time and advice So, the new throttle body was fitted to the car with the old throttle position sensor as I'd struggled to remove its electrical connector when removing the old TB. Unbeknown to me at the time the TPS' mounting bolts holes are slotted to allow some rotation of the unit relative to the TB.. in the absence of any better info I fitted my old TPS to the new TB so that the plug was at approx 6 O'clock when view from the passenger side wing of the car. Next I tried setting up the ECU using this method, however this achieved very little (other than wasting a load of time a fuel) as the car wouldn't idle at less than about 1400rev/min, which would randomly spike to around 2k Alex suggested rotating the TPS with respect to the TB in an effort to offset this issue; and while I thought I'd won (as the adjustment was clearly making a difference to idle speed when carried out while the engine was running) as soon as I drove the car the idle was back up to where it was. As a disclaimer, in retrospect I might not have carried out the ECU calibration procedure above to the letter (I didn't turn the ignition to "Lock" only position 2) so the failure of this to work might be on me.. Anyway, suspecting an issue with the TPS position I attempted to quantify the resistance across its terminals as per this diagram: Long story marginally less long I don't think that these values above are correct for the TPS on my car (perhaps they're for the earlier cable-operated throttle on the pre-facelift cars, which I believe has a different TPS..?). Setting the TPS to give 2.5k Ohms across pins 1&4 when fully closed meant the TPS was noticeably offset clockwise by maybe 5 degrees, and also meant that at fully open the reading across pins 3&4 was something like 0.75k Ohms. In addition to this I found that when fully closed the resistance across pins 1&4 was infinite (not the 2.5k Ohms stated), as it was when fully open across pins 3&4. Evidently this needed a bit more investigation so I cobbled my own TB back together with the TPS from the replacement unit and set about poking it with the multimeter in the comfort of my own home in an effort to validate the results I'd had from the unit on the car. After again setting the TPS to get a reading of around 0.5k Ohms across pins 1&4 with the TB closed gave a value of around 0.76k Ohms across pins 3&4 with it wide open. As with the unit on the car this setting saw the TPS displaced clockwise from the 6 O'clock position. I split the difference between the two readings at around 0.625K Ohms in each case and fiddled with the TPS position to achieve this -ending up with a reading of 0.623k Ohms on pins 1&4 with the throttle closed and 0.622k Ohms across pins 3&4 with it wide open; positioning the TB exactly at the 6 O'clock position as I'd found it on each TB before disassembly. Bear with me, we're getting to the end! I also found that across pins 1&4 from fully closed, as the throttle was opened the resistance value rose from 0.623k Ohms to a peak of 2k Ohms at around 50% throttle opening, before going to infinity beyond this point. In addition I found that across pins 3&4 from fully open, as the throttle was closed the resistance value rose from 0.622k Ohms to a peak of 2k Ohms at around 50% throttle opening, before again going to infinity. So.. in summary it appears when "centralised" the resistance across pins 1&4 measures the throttle position from closed to half open (its value increasing as the throttle becomes more open), after which point the resistance across pins 3&4 takes over (its value decreasing as the throttle opens further). I also found that, unlike as stated in the diagram above, the resistance across pins 2&3 isn't constant / irrespective of throttle position - it changed very much like that of pins 1&4 did over a similar range of values. Armed with this knowledge / the confidence that both TPS units are working correctly I attacked the car this morning. I got the plug off the TPS by removing the unit from the TB and hooking a pick under the steel retaining wire then pulling it off completely (making sure it didn't fly!). You might also have luck in prizing the end of the wire away from the plug at its ends on each side to allow the plug to with withdrawn one side at a time.. I didn't have a flat-bladed screwdriver small enough to try this, though. (Continued below as the forum seems to be imposing some weird word limit..) Last edited by theboymike; May 30th, 2019 at 13:19.