Volvo 240 Rally build

Idle Air Control Valve issue causing the 1500rpm idle?

Might cross over to other problems?

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Last Updated, May30, 2022

Did you check for any codes on the little LED - Jumper box?

If you have LH2.4 and the flywheel pickup there is an issue where the cable from the sensor to the plug breaks internally from the constant flexing as the engine moves. When the cable moves and then goes open you loose the engine timing signal which makes the brain thing the engine has stopped and turns off the spark and injectors. When the engine moves back a bit the wires touch together, the brain sees the engine running and and resumes spark and fuel. Give the cable to the sensor a shake when the car is at idle and see if the engine stumbles or cuts out. It's a pain to change the sensor in situ, but it can be done. This issue doesn't create any diagnostic codes.

Ignore the idle control valve for now, it just bypasses the throttle plate so won't cause engine issues other than high idle or stalling. There is a switch on the throttle plate that enables the idle control when the throttle is closed, and possibly a wide-open throttle switch for full throttle enrichment. You can move the throttle by hand and hear the switches click if things around you are quiet.

As always, look for any possible air leaks from the MAF to the engine, the accordian hoses are known for wearing through if they rub against the body. You can tee in a fuel pressure guage and watch it while you drive to see if you have a failing main or aux. fuel pump. Some fuel rails have a schrader valve on them that can be a handy point to tap in at, and an old mechanical oil pressure guage will work for the test, look for pressure in the ~40PSI range.

LH2.4 isn't too bad to work on. Probably the main issue with retrofits is the grounds, especially the ones for the injectors under the fuel rail M6 bolts. As usual, it'll be simple once you find it.

I should mention a few extra things.

The car has a code reading for the maf. When you hit the gas the car will die unless you very lightly feather the throttle... I assume this is limp mode.

I actually got a replacement maf from the pick n pull. It was buggered too but in a different way. It would allow proper throttle application (at least sitting in the garage, never drove with it) but after a few seconds it would die if allowed to return to idle.

When testing resistance in the MAF harness I made sure to grab the harness with the multimeter hooked up and shook the hell out of everything. The reading never changed from zero ohms so for now I will assume there are no broken wires.

Also where or what is the MAF grounded too? I can't seem to find the actual grounding point so when I tested it I just touched one end of the meter to ground on the battery.

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Robert Culbertson
You might be able to tap into the resources over at TurboBricks. Definitely more knowledgable Volvo pervs over there. But I'll help you as much as I can.

I've always used old OEM Volvo MAFs as replacements, as the rebuilt ones are pretty... Meh for reliability. I have a few bad ones sitting in a box that have worked and failed.

So the problem is probably not the MAF. They rarely go bad unless they're coated in oil or the wire gets broken.

Did you convert the car to LH2.4 from 2.2 or k-jet?

I've had similar issues with my turbo lh2.4 swap-a-palooza Volvo. Once it was the power stage crapping out, the other time it was the hose on the in-tank fuel pump leaking and bypassing the in-tank pump. Both had very similar symptoms: runs great for a bit (~1hr), and then it starts to stumble really bad and die after a minute of erratic running. Let the car sit for an hour and there would be no problem for a few more hours of driving.

All this to say, it could be something completely unrelated to the MAF that's causing your car to run like poo. Oh the joys of 30 year old engine management computers, crappy wiring, old components, and bad luck.

To that last comment... yup. There's a reason im wanting to rid of this system in the near future.


First off it is not a swapped setup. The car has always been lh.2.4.

I will check the in tank pump and figure out if I can test the power stage. Maybe I can figure out the reason for the random misfires.

The replacement MAF was a new walker unit. So shouldn't (in theory) have the issues associated with a rebuilt one.

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Not Trolling
Idle Air Control Valve issue causing the 1500rpm idle?

Might cross over to other problems?

I think it is... I grabbed a spare and cleaned it out. Tried it and the idle went down to 500 which is slow. That could just be a really inaccurate tach, not sure. Haven't looked to see if the idle can be adjusted yet.

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Martin Loveridge
Did you check for any codes on the little LED - Jumper box?

If you have LH2.4 and the flywheel pickup there is an issue where the cable from the sensor to the plug breaks internally from the constant flexing as the engine moves. When the cable moves and then goes open you loose the engine timing signal which makes the brain thing the engine has stopped and turns off the spark and injectors. When the engine moves back a bit the wires touch together, the brain sees the engine running and and resumes spark and fuel. Give the cable to the sensor a shake when the car is at idle and see if the engine stumbles or cuts out. It's a pain to change the sensor in situ, but it can be done. This issue doesn't create any diagnostic codes.

Ignore the idle control valve for now, it just bypasses the throttle plate so won't cause engine issues other than high idle or stalling. There is a switch on the throttle plate that enables the idle control when the throttle is closed, and possibly a wide-open throttle switch for full throttle enrichment. You can move the throttle by hand and hear the switches click if things around you are quiet.

As always, look for any possible air leaks from the MAF to the engine, the accordian hoses are known for wearing through if they rub against the body. You can tee in a fuel pressure guage and watch it while you drive to see if you have a failing main or aux. fuel pump. Some fuel rails have a schrader valve on them that can be a handy point to tap in at, and an old mechanical oil pressure guage will work for the test, look for pressure in the ~40PSI range.

LH2.4 isn't too bad to work on. Probably the main issue with retrofits is the grounds, especially the ones for the injectors under the fuel rail M6 bolts. As usual, it'll be simple once you find it.

I never thought about the crank sensor wire on the flywheel sensor. Will definitely see if I can come up with something there.

Yes I have gone through all the codes, got 1-2-1 aka MAF. Forget the other code but its for the vehicle speed sensor which as far as I can tell should not matter. This is just because the speed sensor isn't hooked up.

I wanted to check the fuel pressure but the gauge I have won't tie in to the volvo injector rail. I will make a better effort to check though, should be able to come up with something. The car will run with just the main pump working ( i have tried disconnecting the tank up while its running and it made no difference). So is it possible that I would still get 40ish psi with just the main pump working?

1) Loveridge knows volvos.

2) Have you ruled out an ECU problem?

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First Rally attended (2000), First Rally competed in (2001)
Cars Built (1), Engines Built (0) Cages Built (0)
Driver (8), Co-Driver (47), Drivers (19)
Clerk (29), Steward (1), Official (17), Volunteer (5)
WRC Spectator (1), WRC Photographer (6), WRC Observer (4)
Rallies attended (120) Countries attended rallies in (11)
Last Updated, May30, 2022

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Eric Ewert
I never thought about the crank sensor wire on the flywheel sensor. Will definitely see if I can come up with something there.

Yes I have gone through all the codes, got 1-2-1 aka MAF. Forget the other code but its for the vehicle speed sensor which as far as I can tell should not matter. This is just because the speed sensor isn't hooked up.

The no speed sensor will cause all sorts of fun hunting between 800-2000rpm, bujt no stalling to my knowledge or experience. I got around the speed signal issue by swapping on a LH2.2 throttle body. It has an air-bleed to dial in the idle speed, and the LH2.4 throttle switch/TPS bolts right on.

Yes Keith, I have a spare ecu and tried it, made no difference.

Robert why would the vehicle speed sensor play any roll when its sitting idling and not moving? Does it need to see that nothing is happening? Also I may try and see if I can wire the toyota axle speed sensor into it. Hopefully the sensors are similar enough that it doesn't matter.

Eric is entirely correct in his reasoning on the vehicle speed sensor. Through the ECU it drives the speedometer and cruise control and turns on the annoying upshift light until the brain figures you must be in fifth. Absolutely nothing to do with engine management, in some of my 240's I've gone for weeks without having it hooked up. 637,000 km on my '93 240 daily driver and never replaced a MAF or ECU.

You could try a reverse test on your MAF's, swap them into a known good running car and see how they work. As you pointed out you do have a MAF code showing but that doesn't necessarily mean that the MAF is bad. Carefully peel back the boot on the MAF wire harness and look at the back of the connector for broken wires or corrosion.

Try running the engine with the MAF unplugged. It should still run albeit without much power. If the way the engine runs with and without the MAF is different, I'd guess the MAF is OK.

Robert alludes to a Throttle Position Sensor; there is none. Just the 2 micro switches on the throttle body. The one that changes state at closed throttle feeds the fuel module. Pin 3 on the switch module, probably a blue/red wire. When you close the throttle from above 1500RPM the fuel brain shuts off the injectors until the rpm's fall below 1500 to save fuel and overrun exhaust noise.

Wide Open Throttle (WOT) pulls a yellow/white wire to ground and signals both the fuel and ignition brains, probably over-riding the O2 sensor and adding a bit more advance. The switch pulls the inputs on the brains to ground, if there was a problem here it might give you some strange engine running.

The throttle being closed also enables the idle control motor, which is just a 1/4 turn valve with a coil to open it and coil to close it. They are PWM'd so a 50/50 signal to open and close gives you the valve open half way, Feedback to the idle control is the engine RPM, and the setpoint is biased by the temperature sensor to give a slightly faster idle on a cold engine. It's a great system, you should be able to ease up on the clutch and pull away on level ground without touching the throttle. The manual bypass on the LH2.2 was just the same as wedging your throttle open a bit, which is what carburetors had.

Because the WOT switch appears to affect the ignition timing and you seem to have idle problems, take a look at the switch module and it's wiring. It's quick to do with a multimeter. I can send you a scan on the drawing if you want but I'm guessing you have wiring diagram manual anyway.

And again, check for air leaks especially in the accordion plastic hose. It's possible that you'll get a MAF code if the engine running lean from an intake air leak. Stick your hand over the MAF inlet with the engine running, it should pull a decent vacuum and stall.

Stick with it, fixing the LH2.4 is better than switching to Carbs. I had some DCOE48's on a 2L 142 with an R cam, nice high end power but not good for daily driving. You've done so much great work on the car already, it just needs a little more time.

P.S. I'm guessing the Toyota sensor will work for the speedometer but I don't have a clue how the tone ring in the Toyota axle compares to the Volvo, so the speedometer could be way off. You could build a little box to fix that it really mattered to you.

Martin as I mentioned I checked the harness going to the MAF, cleaned and doubled checked. Couldn't find any breaks or problems that way.

Unfortunately it runs no different with or without the MAF so i'd say its safe to say its dead. But again it passes all the checks so maybe there is hope.

I just tried to jump the in tank pump and got NO sound out of it. Assuming I did this correctly (removed fused 4 and 6, jumped the right side of the fuse panel) its probably dead. However I first need to check the harness to the in tank pump before condemning it.

For the record the main pump seams to be happy.

Now could this be the cause of dead mafs? The tank pump wiring goes through the fuel pump relay of course, within the fuel pump relay it is connected to the maf (orange wire, terminal 5 on the maf).
Could this actually cause dead MAF's??

Also martin or robert could you give me your feedback on the differences between the two mafs I posted? I got a response back from the seller saying they have sold quite a few as replacements so should be ok. Just want to be certain.

Update on this: It looks like I am not getting power to the in tank pump. Stupid question but does the car have to be running for it to power up?

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Eric Ewert
Also martin or robert could you give me your feedback on the differences between the two mafs I posted? I got a response back from the seller saying they have sold quite a few as replacements so should be ok. Just want to be certain.

Update on this: It looks like I am not getting power to the in tank pump. Stupid question but does the car have to be running for it to power up?

Not sure on the MAFs (or what the question was), I'm not that crazy of a volvo perv

The pumps will both momentarily get power when the ignition is switched on, and then they will both get continuous power once the engine is turning (either starter motor or by running).

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Eric Ewert
Robert why would the vehicle speed sensor play any roll when its sitting idling and not moving? Does it need to see that nothing is happening? Also I may try and see if I can wire the toyota axle speed sensor into it. Hopefully the sensors are similar enough that it doesn't matter.

The speed sensor tells the ECU when the car is moving vs standing still. On my car the decel fuel cut kicks off around 2k rpm, so it's probably not for fuel cut. I have no idea what the ECUs do with this info, but I do know that it is a VERY common problem with LH2.4 cars, though it might be only with certain ECUs.

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Martin Loveridge
Eric is entirely correct in his reasoning on the vehicle speed sensor. Through the ECU it drives the speedometer and cruise control and turns on the annoying upshift light until the brain figures you must be in fifth. Absolutely nothing to do with engine management, in some of my 240's I've gone for weeks without having it hooked up.

I'm not sure what you were trying to say there? There is a wire (cruise control maybe...?) that goes from the gauge cluster over to the ECU. You do not need an ECU to drive the speedometer, the power and signal wires to the speed sensor in the diff are only connected through the gauge cluster.

After poking around further discovered what you just said Robert: the pump(s) only get continuous power when running.

So on discovering that I simply tried to power up the in tank pump while the car was not running (igniton on of course). Still the intank pump made zero noise. Looks like I will be ordering one up tomorrow.

As far as the maf just wondering if the internal differences are actually a problem or is it just a different design? I only care because I don't want to plug it in and have it do damage or get damaged.

And now to study for midterms... rally and school really don't mix all that well!!! You have been warned young(er) people looking at this. I don't know how some manage it.

I usually swap to the 740 turbo in-tank pumps. You have to shorten the steel pickup tube, but that's the only modification. Also make sure to get fuel submersible hose for the 4in section in the tank. Most everything else will fall apart.
It's what IPD sells as their "Performance Upgrade" 240 pump.

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Robert Culbertson
I usually swap to the 740 turbo in-tank pumps. You have to shorten the steel pickup tube, but that's the only modification. Also make sure to get fuel submersible hose for the 4in section in the tank. Most everything else will fall apart.
It's what IPD sells as their "Performance Upgrade" 240 pump.

Same PUMP and I believe same part number for 240, 740, Xratty, 900 Saab, and a long list of other cars...LONG list..

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john vanlandingham

Same PUMP and I believe same part number for 240, 740, Xratty, 900 Saab, and a long list of other cars...LONG list..

I'm sure they will all fit. The 740 turbo in-tank pump is substantially larger than the stock (and replacement) 240 ones (longer and bigger diameter). The 740 Turbo pump is about the same size as a Walbro 255 or a 5.oh Mustang pump.

To Eric:
You can also just slap a Walbro 255, or a fox-body mustang pump in the tank if you want. Then you can rid yourself of the wrong 2-pump system (the right 2-pump system is mo bettah though). You may need to upgrade your fuel lines though, depending on what you installed when you built the car.