Cleaning the throttle body is never of course of mistake, especially if it's been a while, but I'd suggest that there's a good likelihood that your problem is the IAC valve, or maybe even the TPS.

I cleaned my throttle body last summer, and my idle went way up. Mine is an '86 240 LH2.2, so I have the thumbscrew for idle adjust on the throttle body. There's a test point that gets grounded which closes the IAC, at which time you adjust the thumbscrew. After the cleaning, with the thumbscrew in fully, the idle was still a bit high. I assumed my IAC was fine, because before the cleaning, I was able to make what seemed to be the appropriate adjustment.

A while ago, the stumbles you referred to on idle-to-acceleration started happening frequently. It happened when coasting on a highway also, if I then punched the accelerator a bit. Since the frequently advised IAC cleaning was one of the few standard maintenance items I had NEVER done, and this seemed to be an obvious thing to try, since all the problems were during the off-idle transition.

I first ohmmetered the TPS at the ECU, to make sure the ECU was aware of when the throttle was at rest. I then pulled the IAC. It failed the "spin on axis" test miserably. (It's supposed to spin freely on its axis, and click at the mechanical endstops). This test only works on 240s with the 3-pin 501 or 520 valve, which is not spring-loaded, and just floats with not voltage applied. Yours is spring-loaded, which makes verification more difficult.

There are many descriptions of cleaning in the archives. I started with throttle body cleaner, but carb cleaner may be a bit better (stronger). Hold it with the openings on the bottom, cover one port, and spray into the other. Swish around for a while, then dump out and repeat. Don't allow any cleaner to flow into the motor end. I could do the spin-on-axis test with my 501, and wasn't making good progress, so I tried something else that may work well for the 940s spring-loaded 516 valve.

I put the valve end into 1 inch of mineral spirits, and applied voltage to the pins at the top to exercise the valve. I believe in your case, 12 volts gets applied to pin 1, and ground to pin 2. You should verify this yourself, but I believe that if you did do it the wrong way for a split second (ie. 1/100th!) it wouldn't damage it. Anyway, after a minute or so of this, I'd take in out and do the carb cleaner "switsh", and so on. After a few cycles of mineral spirits/carb cleaner it should free up pretty well. Hopefully you'll be able to hear the difference in its response when voltage is applied.


I don't think in the future that I'll ever do a throttle body cleaning without also cleaning the IAC.


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David Armstrong - '86 240(350k km?), '93 940T(270k km), '89 240(parts source for others) near Toronto