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700/900 Series General Forum for the Volvo 740, 760, 780, 940, 960 & S/V90 cars |
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940 High Idle after WOTViews : 336 Replies : 4Users Viewing This Thread : |
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Oct 2nd, 2023, 19:28 | #1 |
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940 High Idle after WOT
Hi,
Can anyone point me in the right direction, Got a high idle rpm that only appears after WOT. If I turn car back off and back on, it solves the problem. I've checked TPS Sensor, MAF, Calibrated Idle to 500rpm with IAC clamped. Benchtested IAC Valve and cleaned. Not sure how to proceed. Tested wiring and wiring is all good to the IAC Valve. Thank you |
Oct 2nd, 2023, 19:59 | #2 |
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Last Online: May 8th, 2024 14:49
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Location: London and Cambridge
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Hi,
The issue is the ecu is no longer seeing the speed signal from the speedo to pin 34 on the ecu- that signal tells the ecu to activate the idle circuit, without it the car will idle at high rpm as you’ve found. Does your speedo work? Cheers |
Oct 2nd, 2023, 22:53 | #3 | |
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Last Online: Oct 3rd, 2023 19:55
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Quote:
Yes, speedo currently works. But have not investigated the wiring to the ECU telling vehicle speed. How do you suggest I proceed? Thank you |
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Oct 4th, 2023, 19:40 | #4 |
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Last Online: May 8th, 2024 14:49
Join Date: Nov 2012
Location: London and Cambridge
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Hi,
Whilst I know what the fault is, I’m not sure how to fault find it on a 940 - I’ve got a 240 with a 940 engine in it, so my wiring loom and speedo etc. is different. Hopefully someone else will have some advice. Cheers |
Oct 8th, 2023, 16:02 | #5 |
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Last Online: May 6th, 2024 02:02
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Location: Holywood
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Yep had the same problem with 940 engine in a 360 with no speed sensor. Had to make one, luckily its an option in the speedo so there is a place for it.
I would say its not precisely as described above. The idle mode is triggered by the throttle closed sensor. The ECU just doesn't like not have a VSS signal with WOT, and creates some sort of limp mode, so far noone knows why. Just trace pin 34 (assuming thats the right wire), normally comes from the ABS module to the speedo and then on to the fuel ECU on 34. I've had the rear axle speed sensor in the diff stop working due to chaffing and shorting on the body making the speedo fail, but speedo working and no signal to ECU is quite rare. |
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