95' 940 Rough Idle and Stalling

JaimeMedina · 06-09-2022, 11:50 PM

Hey everyone, I recently decided to replace the air intake hose on my car with the DO88 replacement hose as the old one was cracking and practically falling apart. The previous owner of my car replaced the stock intake box with a CAI, so I decided to replace the filter and properly mount it while I was replacing the intake hose.

After I replaced all the parts and got the intake mounted up, I tried starting up the car and experienced a very rough idle, and the car entirely stalling out when I gave it some gas. I suspected that the MAF sensor may have went, so I got a replacement, but even after replacing the MAF, the same symptoms occurred.

Does anyone have any ideas of what may be going on here? Any help would be greatly appreciated.

Thanks!

Janspeed · 06-10-2022, 08:57 AM

i'd say inspect for vacume leaks, lose hose clamps, between MAF and engine. Also any other hose you might have pulled off for access.
Absolutely NO vacume leaks allowed if you want the system to work like it should.

Also inspect the fuel pressure regulator hose. Is it connected? If not then the fuel pressure is unregulated and the manifold has a big vacume leak.

Once everything is properly connected it should work but because your car is a '95 and (probably) has LH2.4 which has a certain adaptability to the engine it might take some actual driving for the LH-system to fully recalibrate itself.

Acke · 06-10-2022, 11:36 AM

I'd try resetting the ECU (fuel trims) if you made changes in the plumbing between the filter and AMM. I saw quite big AFR changes at idle when I moved my 3" AMM ~1cm further away from the 2,5-3" adapter I use with the stock airbox.

JaimeMedina · 06-10-2022, 05:43 PM

I've went ahead and made sure I didn't have any vacuum leaks whatsoever on all of the connection points. I've noticed that the car will manage to stay on and idle without the MAF connected, although still very rough, but as soon as I try and start the car with the MAF it will start up and die shortly after unless I give it some gas.

I'm not too sure how to go about resetting the maps on the car. I've disconnected the battery and have left it disconnected for about 20 minutes to see if it would reset the ECU by any chance. Haven't checked to see if that would make any difference yet.

Would resetting the maps just involve disconnecting the battery? Or is it a different process?

Janspeed · 06-11-2022, 03:01 PM

leaving the battery power off will reset the ECU. Not the MAPS offcourse. Those are hard coded in an EPROM chip.
The reset will return all self-learn values to default. (short-term and medium term fuel trims) When the battery is reconnected and the car is started the ECU will start 'learning' again based on sensor inputs.

If/when the engine is started and idles without the MAF connected the ECU is using hard coded default settings/values to make the engine run.

According to Volvo documentation the MAF of a LH2.4-system should give 2.5-4.0 Ohms resistance between pin 2 and 3. If you measure and find your measurement to be within spec then the MAF is GOOD. and not the problem.
The real problem can still be something else like a corroded or broken connection in a connector or a broken wire.
Behind each shock tower there are 2 BIG wiring loom connectors. It's worth inspecting those. The can have corroded pins inside them. Clean them up if you find any (use electrical contact cleaner spray)

Acke · 06-12-2022, 01:36 AM

Sorry for the confusion. I meant the fuel trims / ECU, not the actual maps. Thanks Janspeed for writing it better.
OP did you trim the PCV heater element to fit tightly in the intake hose and test it for vacuum leaks as well?

06-09-2022, 11:50 PM	#1
JaimeMedina Newbie Join Date: Aug 2021 Location: Charlotte, NC	95' 940 Rough Idle and Stalling Hey everyone, I recently decided to replace the air intake hose on my car with the DO88 replacement hose as the old one was cracking and practically falling apart. The previous owner of my car replaced the stock intake box with a CAI, so I decided to replace the filter and properly mount it while I was replacing the intake hose. After I replaced all the parts and got the intake mounted up, I tried starting up the car and experienced a very rough idle, and the car entirely stalling out when I gave it some gas. I suspected that the MAF sensor may have went, so I got a replacement, but even after replacing the MAF, the same symptoms occurred. Does anyone have any ideas of what may be going on here? Any help would be greatly appreciated. Thanks!

06-10-2022, 11:36 AM	#3
Acke Board Member Join Date: Feb 2012 Location: Finland	I'd try resetting the ECU (fuel trims) if you made changes in the plumbing between the filter and AMM. I saw quite big AFR changes at idle when I moved my 3" AMM ~1cm further away from the 2,5-3" adapter I use with the stock airbox. Last edited by Acke; 06-12-2022 at 01:02 AM..

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06-10-2022, 08:57 AM	#2
Janspeed Board Member Join Date: Sep 2005	i'd say inspect for vacume leaks, lose hose clamps, between MAF and engine. Also any other hose you might have pulled off for access. Absolutely NO vacume leaks allowed if you want the system to work like it should. Also inspect the fuel pressure regulator hose. Is it connected? If not then the fuel pressure is unregulated and the manifold has a big vacume leak. Once everything is properly connected it should work but because your car is a '95 and (probably) has LH2.4 which has a certain adaptability to the engine it might take some actual driving for the LH-system to fully recalibrate itself.

06-10-2022, 05:43 PM	#4
JaimeMedina Newbie Join Date: Aug 2021 Location: Charlotte, NC	I've went ahead and made sure I didn't have any vacuum leaks whatsoever on all of the connection points. I've noticed that the car will manage to stay on and idle without the MAF connected, although still very rough, but as soon as I try and start the car with the MAF it will start up and die shortly after unless I give it some gas. I'm not too sure how to go about resetting the maps on the car. I've disconnected the battery and have left it disconnected for about 20 minutes to see if it would reset the ECU by any chance. Haven't checked to see if that would make any difference yet. Would resetting the maps just involve disconnecting the battery? Or is it a different process?

06-11-2022, 03:01 PM	#5
Janspeed Board Member Join Date: Sep 2005	leaving the battery power off will reset the ECU. Not the MAPS offcourse. Those are hard coded in an EPROM chip. The reset will return all self-learn values to default. (short-term and medium term fuel trims) When the battery is reconnected and the car is started the ECU will start 'learning' again based on sensor inputs. If/when the engine is started and idles without the MAF connected the ECU is using hard coded default settings/values to make the engine run. According to Volvo documentation the MAF of a LH2.4-system should give 2.5-4.0 Ohms resistance between pin 2 and 3. If you measure and find your measurement to be within spec then the MAF is GOOD. and not the problem. The real problem can still be something else like a corroded or broken connection in a connector or a broken wire. Behind each shock tower there are 2 BIG wiring loom connectors. It's worth inspecting those. The can have corroded pins inside them. Clean them up if you find any (use electrical contact cleaner spray)

06-12-2022, 01:36 AM	#6
Acke Board Member Join Date: Feb 2012 Location: Finland	Sorry for the confusion. I meant the fuel trims / ECU, not the actual maps. Thanks Janspeed for writing it better. OP did you trim the PCV heater element to fit tightly in the intake hose and test it for vacuum leaks as well?