Duh, I forgot something quite obvious to address your problem: RAISE YOUR IDLE SPEED! While it may not be perfectly elegant solution it will keep you from stalling.

 

I'm certainly no expert with the LH 2.4. My wife has a 1990 240 with very few miles; she acquired it last year. I have never had a problem cleaning MAF sensors on other vehicles, but when I cleaned this one, it killed it. I purchased a local junk yard one for $40 which cured the surging, misses. I decided not to clean these on the 240.

 

MAF cleaning is often iffy. hold it so the plug and circuitry is on the top side while you spray it down with that cleaner stuff so it washes the wires and runs out without running into the e-box on the side of the thing.

 

It happens. Were you using Carb cleaner or MAF cleaner

 

in my case, I've always used MAF cleaner. not sure its any different than regular electrical contact/circuit cleaner. the one really troublesome MAF I had was on my 850... would throw periodic faults and run in limp mode. I cleaned it, faults went away for awhile, came back. tied the wire down and back (documented trick online) to keep it farther from the HV coil wire, stopped for awhile, came back. eventual solution was a new MAF :-/

 

That was the only thing that the mechanic I bought it from would bother doing. One of the reasons I never want him to touch it again. He did say that he didn't wan't to raise it any more that he had. Essentially, all he did is adjust the screw stop for the throttle-valve-actuating-lever (or whatever that is called).

I could adjust it some more, but then it would be at a much higher idle all the time. AND I wouldn't know if it was acting up. I have gotten pretty deft at two-footing it when it starts acting up and this way I can monitor it's behavior more accurately to see if anything I do causes any improvement.

Thanks, though.

 

is the idle switch working? disconnect it, clip a multi-meter in OHMS mode across it, and work the throttle by hand, gently (car can/should be off for this test). it should be closed (0 ohms) when the throttle is completely closed, and almost the instant the throttle comes off idle, click open (infinite ohms).

some versions also have a full throttle switch, IMHO, thats less important. the idle switch has to be closed before the ECU will attempt to manage the idle via diddling the idle air controller...

I forget the exact 'proper' setup procedure, but its something like, disconnect the IAC and adjust the idle air screw on the throttle body for about 500rpm idle, then plug in the IAC, and it should idle around 700. its suppose to idle a little higher if it thinks the AC is turned on, maybe 800-900. on a LH 2.4 car, its completely unadjustable past this, as its all digital.

 

My problem is that I can't see the connector well enough (I need upside-down bifocals sometimes) to see which pin is which in the connector. So, that is one of the things I plan to check and adjust when I overhaul the throttle-body. It was also my first suspect, but then I started getting clues that the problem was low fuel pressure.

The spare throttle-linkage clips that I ordered shipped today, so they should be here soon. I already have a throttle-body gasket. So, I am almost ready to pull the throttle-body, clean it, Test the idle switch, then adjust the switch and linkage. I have gotten all the adjustment specs from my Bentley and Haynes manuals. I will adjust the idle-switch while the whole thing is out of the car, using my ohm-meter set to beep mode. Then I will put the throttle-body back in and adjust the throttle-cable, throttle-pulley and throttle-body-linkage.

Hopefully, that will do it.

But I am still going to take Lev's advice and keep going, even after it stops stalling. (If that makes any sense at all.) I am going to work on tuning up, checking, and adjusting everything I can get my hands on under that hood.

Thanks for all your ongoing help.

 

What is the idle speed now?

 

As Pierce stated, the idle speed on the LH2.4 fuel injection system is set by the computer. The screw adjustment on the throttle body isn't an idle speed adjustment, it is to set the stop position of the butterfly valve so the butterfly valve is completely closed at idle. At this position the throttle position switch should click. This engages the Idle Air Controller circuit which will allow just enough air in to keep the idle at around 700 RPM.

A year or so ago, a member here (swiftjustice44) posted a very nice write-up on how to properly set the idle on the LH2.4. Do a search for posts by him.

 

I know. That is why I refer to it as the Throttle-Valve-Stop-Screw, or something like that, when I am talking about it. Screwing it in further is essentially the same as holding your foot on the gas. Which is NOT the same as setting an idle speed, even though it kind of has the same final result.

Funny, though, all the manuals show an idle screw UNDER the throttle-body even for an LH-2.4 on a B230F in a 1993 240. This is a completely separate screw from the Throttle-Valve-Stop-Screw that we are discussing here. So, I don't always trust everything the manuals say or show. (No, I don't have Greenbooks, just the Bentley, Haynes, and Chilton's.) I just use then for additional clues. Fun, fun.

 

Yeah, those manuals aren't very accurate. The LH2.2 system had the idle mixture screw under the throttle body. The LH2.4 had no such thing.

 

I am just writing to let everyone know that I am almost positive that I have solved the problem.

I pulled out the throttle-body and cleaned it. It was only a little gunked up. Nothing terrible. While I had it out, I was able to double check the idle switch. It was definitely NOT closing while at idle. So, I was able to adjust the throttle-valve-stop-screw, based on a visual inspection of the actual position of the throttle-valve. I set the position just far enough to keep the valve from sticking in the throttle-body when closed. Then I was able to adjust the position of the idle-switch both by listening for the click and by using my ohm-meter.

One thing I should point out to anyone reading this: It is possible to twist the idle-switch too far in the "throttle open" direction and still have the switch feel as if it is clicking with the same amount of turn of the valve. If you turn the switch too far then it just forces the throttle-valve open a bit. The switch itself will not allow the valve shaft it is mounted on to rotate very far at all (with respect to the switch itself) past the point where the switch is closed. So, you want to position the idle switch so that it has just barely been clicked closed (with the valve closed) and there is the tiniest bit of pressure against the rotation of the shaft in the "throttle open" direction, but no further. If you go too far then it is almost the same as setting the throttle-valve-stop-screw to hold the valve partially open.

I pulled out the idle-air-valve and cleaned it, though it was pretty darn clean already. I also connected its electrical connector and ran the ECU tests while looking directly at the valve to make sure that it did its thing, and it passed with flying colors.

After adjusting the throttle-body and putting it back in, I put the linkage back on and adjusted it. That was definitely a bit more troublesome. It became easier when I realized the purpose of the adjustment method listed in the Bentley manual was to ensure that when the throttle pulley is all the way back at the stop, that the throttle valve will be closed far enough to make sure the idle switch makes contact. If the linkage and the throttle-pulley "conspire" to hold the throttle just a little bit open, then the idle switch will never make contact and the idle-air-valve will never be able to do its job. So, as long as the throttle-valve can close all the way to the stop when your foot is off the gas while still allowing the throttle-pulley to go all the way back to its "zero-throttle-stop" then I figure you are good.

So, with everything back together I started the car up and ran it on a torture test. I drove around for hours as slow as I could, driving in a way that simulated the worst of the traffic that I ever encounter. I even accelerated up to about 20 MPH and slammed on the brakes a few times, because sometimes it would stall when I had to hit the brakes. (Fortunately, there is an "abandoned" navy base on Alameda Island where I could drive like a granny without pissing people off.) I absolutely could not get the thing to stall.


There is just one last thing that seems to be a little off. When the engine is idling and I turn the throttle-pulley by hand, when I first start to turn it, just as the idle-switch opens, the RPMs drop quite a bit. It is as if the idle switch is disengaging before the throttle-valve has had a chance to open enough to let enough air in. This is not a problem in normal driving because I never press on the gas as slowly as I was turning the throttle-pulley by hand. However, this doesn't seem quite normal either.

Could it be that I have set the throttle-valve-stop-screw too far out, letting the default position of the throttle-valve be "too far closed"? I know, that sentence sounds contrary to all the manuals which say to adjust the stop so the valve is exactly closed. But what do you do about that slight delay between when the idle-switch opens and when the throttle-valve is open far enough to let an equivalent amount of air pass through?

Here is a related question: On the throttle-body, there are two vacuum hoses that fit onto brass fittings on the top. On my throttle-body, when the valve is closed, the holes for those two vacuum hoses are on the non-vacuum side of the valve. In other words, the valve is positioned such that the valve is between the intake manifold and those holes, so the holes are on the side facing the air duct where there is no vacuum at the time. As the valve opens, it brushes past those holes and the holes are now on the vacuum side of the valve. Is the valve suppose to be positioned such that those holes are always in the vacuum side? Or is the throttle-body designed such that as the valve opens, vacuum is applied to those holes which then activates some other system via the vacuum action?

Thanks

 

one of those two vacuum lines on top goes to the charcoal cannister purge circuit, I'd imagine its intended to only suck stuff in when the engine is running relatively wide open. I forget where the other one goes, but its probably something similar.

 

The canister purge lines valve should only be open during mid throttle operation. That's when a vacuum bleed (leak) wouldn't be noticeable and the system can pull fumes off the canister without impacting low speed idle or high speed power.
If the valve is bad and staying open that would be a cause for a vacuum leak and poor idle or even stalling.

 

Wondered what remedies proved to be most helpful?