Volvo Owners Club Forum - View Single Post - 240 General:

TheHungriestBadger · Jul 19th, 2022, 23:19

Hi all, got an interesting one for you (or maybe not, who knows). I have a 1990 240GL Auto with a B200F and AW70. Recently, I have noticed that when idling in Park or Neutral, the revs rise up, completely on their own after about 10-20 seconds. This is regardless of user input, or lack thereof; pressing/releasing the brakes doesn't trigger it, nor does a quick rev of the engine. Revving the engine briefly and then releasing the throttle also does not 'reset' the idle speed. Turning the engine off and back on again also does not 'reset' the idle speed.

The revs rise from about 750rpm to about 1,000rpm. This is only observable on a hot engine due to the faster idle when 'cold' - cold idle is not affected and is a perfectly normal value.

The only thing that makes the revs behave properly is engaging Drive or Reverse. When in gear, the revs stay bang on 750rpm as they should with no bouncing of the tacho whatsoever.

Staying in gear prevents the revs from rising, and shifting into gear brings the idle back to 750rpm after it has risen (again, indefinitely).

I know that the Throttle Position Switch is functional (clicks + buzzed out for continuity with DMM + verified working using the diagnostics box).

The throttle plate itself must be set correctly given that the idle is fine when in gear. Similar reasoning also leads me to believe the IAC is fine too (it's been cleaned within the last 6 weeks and clicks when the relevant diagnostic test is run).

So does anyone have any ideas on what it could be or any additional tests I could run to help isolate the fault (although 'swap in a known good one' is not an option).

I do have slight suspicion toward the Fuel Pressure Regulator: takes a few rotations of the engine before firing up, although always starts fine hot or cold, and I have on occasion had a petrol smell (no drips of fuel though) from the vacuum pipe that connects to it, although it did have a split at one end and has been replaced recently. Would the main issue be another symptom of a faulty FPR?

The only other thing I can think of is the P/N detection switch on the transmission or whatever it's actually called? Will run the diagnostic test on that soon.

I appreciate this is a long one so thanks for sitting through it.

Regards,
Adam

P.S. If it would help, I can get a video of it.

Jul 19th, 2022, 23:19	#1
TheHungriestBadger Junior Member Last Online: Feb 18th, 2024 23:05 Join Date: Jun 2022 Location: Ardleigh, Colchester	High Idle Only In N & P Hi all, got an interesting one for you (or maybe not, who knows). I have a 1990 240GL Auto with a B200F and AW70. Recently, I have noticed that when idling in Park or Neutral, the revs rise up, completely on their own *after* about 10-20 seconds. This is regardless of user input, or lack thereof; pressing/releasing the brakes doesn't trigger it, nor does a quick rev of the engine. Revving the engine briefly and then releasing the throttle also does not 'reset' the idle speed. Turning the engine off and back on again also does not 'reset' the idle speed. The revs rise from about 750rpm to about 1,000rpm. This is only observable on a hot engine due to the faster idle when 'cold' - cold idle is not affected and is a perfectly normal value. The only thing that makes the revs behave properly is engaging Drive or Reverse. When in gear, the revs stay bang on 750rpm as they should with no bouncing of the tacho whatsoever. Staying in gear prevents the revs from rising, and shifting into gear brings the idle back to 750rpm after it has risen (again, indefinitely). I know that the Throttle Position Switch is functional (clicks + buzzed out for continuity with DMM + verified working using the diagnostics box). The throttle plate itself must be set correctly given that the idle is fine when in gear. Similar reasoning also leads me to believe the IAC is fine too (it's been cleaned within the last 6 weeks and clicks when the relevant diagnostic test is run). So does anyone have any ideas on what it could be or any additional tests I could run to help isolate the fault (although 'swap in a known good one' is not an option). I do have slight suspicion toward the Fuel Pressure Regulator: takes a few rotations of the engine before firing up, although always starts fine hot or cold, and I have on occasion had a petrol smell (no drips of fuel though) from the vacuum pipe that connects to it, although it did have a split at one end and has been replaced recently. Would the main issue be another symptom of a faulty FPR? The only other thing I can think of is the P/N detection switch on the transmission or whatever it's actually called? Will run the diagnostic test on that soon. I appreciate this is a long one so thanks for sitting through it. Regards, Adam P.S. If it would help, I can get a video of it.