'88 240 idling too rich, adjustment screw?
 

Hi. Well the wagon has been running great, but it won't pass emissions. Fine at 2,400 rpm, but not at idle. Too rich?
idled smooth enough, maybe a little vibration. Tail pipe has black soot, but I think it's left over from a bad MAFS i changed. I don't see black smoke, but does smell exhausty.

I changed plugs, new MAFS, cleaned crankcase ventilation system, and checked all hoses. Everything right and buckled up. Runs great on the road.
There is an adjustment turn knob on throttle body. Is this for lean/rich fuel mixture? There is also a big brass screw on the MASF that looks like an adjustment screw. It's next to the plug.

Any ideas would be helpful.
Hope all you from U.S. had a great Thanksgiving.

OX sensor ? there's an easy test of their functioning... on a 240, the connectors are near the wiper motor on the engine side of the firewall, there's a square 2-pin heater connector and a round 1-pin signal connector. unplug the signal connector, wrap a single strand of thin copper wire around the pin, put the connector back together with the end of that wire hanging out... connect a volt meter between that wire and chassis ground, set the volt meter for DC Volts, start the engine and let it warm up so its at its normal idle speed.... the voltage you read should be going up and down, a low value around 0.2 to 0.3V, and a high value around 0.7 to 0.9V (the actual values aren't important, just that its swinging from less than 0.5 to more than 0.5 and back). if its swinging every couple seconds, the lambda (oxygen balance) is good, if its taking more like 10 seconds per swing, the OX sensor is nearly shot, if its stuck high or low, the sensor is completely shot, or something is wrong with the engine management.

if the ox sensor is good, then you may need a new catalytic converter, I've typically had to replace these around 300K miles, give or take, on cars that were always well maintained. if the car ran way too rich for awhile, the cat can get pretty flugged up, sometimes an 'italian tuneup' can clear it out, drive on an open highway for about an hour in 3rd gear rather than overdrive, heavy on the throttle, as fast as you dare go.... the idea is to keep the engine up around 4000-5000 RPM to get the cat really hot.... back off and drive normally for 5 minutes before stopping to let it cool back down.

Ha Ha pierce!
 

I did give it the old Italian tunup, as it had run bad for awhile due to the MAFS. Took it out and ran it flat out several times, as well as 30-40 minutes at 80. (He's rock solid at at 100 plus) The test said catalytic converter passed.

could be the O2. My neighbour has the meter, but I'll check with your tip when he gets home. The O2 sensor is on the exhaust manifold , correct? I've never changed one but it looks easy to get at. I may just get a new one and put it in. 31 year old car. Has to be done eventually.

but what is that thumb wheel on the throttle body?

the adjustment on the throttle body is for setting idle baseline. I believe the procedure is to warm up the engine, with it in park and all accessories shut off, unplug the idle air controller, then tweak the throttle air adjustment for a baseline idle speed (I think its 500 or 600 RPM?)...

there IS another adjustment on LH 2.2 cars, the MAF has a set screw, but to adjust this you really need an exhaust gas tester, which you stick in a bunghole near the Ox sensor (so you're measuring the gas prior to the cat), then adjust the screw for some baseline free oxygen ratio... LH2.4 did away with this and 'learns' the optimal mixture as you drive and remembers it.

Ahhh, that answers a few questions....
 

I knew these two adjusting type screws did something. This is good info, because the idle is a tad high, and who knows what the factory did about pre-setting the MAFS. This is not a "smart" MAFS, so adjustment may make a big difference in air/fuel ratio, and thus emissions. I do think O2 is worst offender ( He's throwing out twice the allowable emissions, but only at idle.) But any other little tweaks can help. There is a little Swedish/German shop in town that also does emissions testing. I'll take it there after I check/change the O2 sensor. If it fails again I'll have him tweak these adjustments with it on the emissions tester and see if we can get a pass.

Peirce, you're a real treasure on this forum. A huge thanks for all your help!

which emission is high? CO or HC ?

Emissions results for Mr. Bobbles,
 

I looked at this closer after your question. Revealing.

low speed rpm=781 ( So idle is a bit high)
HC=470. . Limit= 200 (assume this is hydrocarbon)
CO=10.67. Limit=1.2
CO2=7.9 No limit given
O2=0.53. Ditto

High speed rpm=2609
HC=158. Limit=200
CO=1.15. Limit=1.20
CO2=13.8
02=0.48

you may be right about the catalytic converter. I think now this problem existed longer than I thought, and last owner sold it on after replacing the fuel regulator because his mechanic told him what a new MASF, CAT, and O2 sensor would cost. Who knows how long he drove it like that though. The new MAFS cleared up the black sooty exhaust and intermittent non driving problem, but maybe the damage was done. Plus the 02 sensor is probably bad too.
here's a possibly related clue. Three times I've had a no start. Every time it was after the car was run for a short period ( 5 minutes or less than a minute, ) after a cold start. If I left it for 15 minutes or overnight, it would start normally. Last time was at gas station a few blocks from me, drove car from cold less than say five minutes from home. I stopped on wrong side of pump, and immediately went to restart and move car, and no start. Let it sit for 15 minutes and started normal. In fact it idled and ran much better upon restart. Very smooth and nice. I have no idea if this is related, just FYI.

OH, a LH2.2 car, the ignition timing is checked the old fashion way, with a timing light, and set by rotating the distributor.... wrong ignition advance can cause high HC due to incomplete combustion.

OMG, duh, of course! I'm not thinking...
 

I completely forgot about timing! So simple. I got caught up in sensors and compters. AND the whole reason I bought this car was his simplicity. I'm a dope. I'll check that when I check O2sensor. My neighbour (Army Engineer) has a timing light.
Thanks buddy!
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That helped...
 

Can't check timing now, no light. But I took off distributor cap and cleaned contacts and rotor. Seemed to help a little. I left these alone when I did plugs as they looked newer and in good nick. I also marked the thumb wheel on throttle body and turned a full turn each way. Clockwise seemed to lower idle a hair. Just by ear and feel, no tach. This is not like a carburator, where a quarter turn makes a significant difference. The timing will be the key. That just makes sense, and I feel it is off a bit. I have been having low expectations about his running as he's 31 years old, but now I see i should expect top performance.

Also, when i restarted at the gas station after no start ( from above post,) I actually thought he'd died, the engine was idling so smoothly and quietly. If you have any thoughts on this situation,and if it's related, I'd appreciate it. Whatever is causing it, when it's working properly, the car runs beautifully, which is why I didn't think any of the other components where bad. Now I realise that it's usually NOT running so perfectly, but just a tad off. Then suddenly he runs like a dream. Can an 02 sensor work intermittently? Bad wire? I'm over-thinking.

List: check timing
Check O2 sensor
Go from there.
Off to work. Have a great day.

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before adjusting the idle bypass in the throttle body, you need to disconnect the idle air controller's electric plug so its disabled, THEN you set the idle for about 500 with a warmed up engine with everything accessory turned off (so no extra loads on the motor), then with the IAC plugged in, it should idle at about 700

88 wagon, that screw you see on the Air Mass Meter ( that's what Volvo calls their Mass Air Flow Sensor) is indeed an adjustment device. The LH 2.2 models ('86-88) had them. They are inset into the plastic tube because there is a "tamperproof" plug made out of aluminum that is screwed into it. Difficult but possible to remove, it provides access for "professional technicians" to make adjustments. Pierce is right, ideally you would be testing with a three gas analyzer . I have in my notes with my car an alternative method, and I will repeat these for you-
Disconnect the O2 sensor wire and connect a volt-ohmmeter to the cable. With the engine warm and at idle, adjust the AMM screw so that the voltage reads 0.6 to 0.7 volts. Reconnect the o2 sensor and check that the voltage swings above and below 0.5V.
With the engine off and the AMM disconnected use the ohm selection of the meter to measure the impedence between pins 3 and 6. It should read 380 ohms.
Next measure between pins 6 and 2.Should be ~ 1000 ohms.
Finally, between pins 2 and 3 you should see 3.5 to 4.0 ohms between pins 2 and 3.
BTW, when these cars were newer, the absence of the plug was evidence of illegal tampering and an automatic fail. Not sure if today's smog techs will be prompted to look for it. I would fabricate something to cover the hole ; would also help keep dirt out of the AMM.

Just out of curiosity, what are the NOx results from your smog test? It should be included in your print out with the rest of the numbers. Even If it were within limits, that would be helpful to diagnose your problem(s). What state are you from?
In the usual sequence of testing, the low speed or idle test is done first, followed by the high speed. Your car is showing signs of a weak cat. The cat is not yet warmed up during the first part; after the cat has "lit up" from a lot of exhaust gases flowing through it, it performs barely adequately. If your cat was "prewarmed" just before the test by a fast idle in the parking lot while waiting your turn in the bay, you may be able to pass this test.