1984 244DL B23F

Trying to get the idle to work right on this car... It's a new acquisition.

Disassembled, cursed at, cleaned, and reassembled the IAC. No improvement.

Car does now start with a high idle for 2 seconds like it should, then drops from 1500 straight down to 250, then roller coasters up and down.

I have set the TPS correctly and cleaned the TB.

I unplugged the AMM after starting it and all of a sudden, lo and behold - it idles at 750rpm. Granted it's a crappy idle, but it's idling right.

Anything I can check or repair on the AMM? Sounds like it's bad to me.

Thanks,
William

PS I have a 740T parked on the street 50 feet from this car. Can I swap in its AMM?
PPS: Idled consistently after warming up, when I had the idle jimmied up high with the throttle linkage.
--
1990 740 Turbo, on its way to stock specs, maybe beyond

"Anything I can check or repair on the AMM?"

Not that I know of. I think Art Benstien's test is to measure it's output by peeling the connector boot back so you can back-probe a meter lead on the output and look for at least 1.5 volts at idle. On your '84 AMM the Red-White wire would be the one to back-probe.

"I have a 740T... Can I swap in its AMM?"

No. The '83-'84 AMM is unique to those years.

I think the AMM effect you're seeing is misleading and possibly due to the ECU reverting to "default" parameters when the AMM signal "goes away", thus masking some unknown condition.

--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

OOooooh, all kinds of bad news!
Haha, thanks though, I'd much rather know.

I found (a few minutes ago) the same thing. Only a -002 AMM will work.

Time to go to the bank and to unpack my AMM cleaner and multimeter from my storage unit.

Do you have any ideas what else might be hidden by unplugging the AMM?

I have a feeling the 26 y/o O2 sensor is worn out.. perhaps even the original.
--
1990 740 Turbo, on its way to stock specs, maybe beyond

"Time to go to the bank and to unpack my AMM cleaner and multimeter from my storage unit."

Don't waste your time. To my knowledge no one has ever found or fixed an AMM problem with a multimeter or cleaner. If it needed cleaning, I think Bosch or Volvo would have pushed for it years ago.

Are you down to just this idle problem now?

--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

I'm down to getting the idle fixed, Checking power to the OD solenoid and swapping its fluid, and finding out why the dash temp gauge reads zero.

For today, all I'm working on is the idle problem.

I'll see if it has good (1.2 minimum, 1.4+ preferred) voltage at the AMM connector - car not running in KP2. Already called around, no nearby yards think they have a compatible AMM. Boo.

--
1990 740 Turbo, on its way to stock specs, maybe beyond

"For today, all I'm working on is the idle problem."

Them why concentrate on the AMM? I don't think it's known to affect idle stability. Not like the more common vacuum leaks. Is there any pattern or rhythm to the idle variations, such as might relate to just one cylinder?
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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Well, I'm concentrating on the AMM because it was idling in a specific pattern (rev to 1500, drop idle to nearly 200 and almost stall, rev back to 1500, repeat).
Once I disconnected the AMM, the idle stopped fluctuating and stayed steady at 750. There are only 3 actual vacuum hoses I see on the engine - 2 for the charcoal canister, 1 for the ECU. The one to the ECU is the only one that looks semi-old. Maybe I should re-check the bellows hose for intake leaks.

--
1990 740 Turbo, on its way to stock specs, maybe beyond

Bellows are good. I took the tube off, covered the ends and blew into it. It held quite a lot of pressure.

I don't think anything else could have a large enough leak to screw up the idle this much.


How do I test the temp sensor?
--
1990 740 Turbo, on its way to stock specs, maybe beyond

Intake gasket?

Do you think an intake gasket leak would leak enough to get the revs up to 1500?

I'll check it, if someone will remind what I AM supposed to spray on it, and what I'm NOT supposed to spray on it.

I really think it's the AMM. The 002 models have some of the highest failure rates.
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1990 740 Turbo, on its way to stock specs, maybe beyond

Yes to the revs.Do not load up the dog house with a flammable spray as its a little too early for the forth of July,some folks use propane,I prefer a spray bottle with water,if you do have an intake leak the water will cause the idle to drop and might even clean the valves.good luck

Do not over look the underused,inexpensive,extremely helpful vacuum gauge.A great tool with many uses.

I was thinking about a vacuum gauge this morning. The car runs (and idles) much better with the AMM disconnected, though it's obviously rich, since I can smell a rich mixture at every stoplight.

Where is the test for the Temp sensor?
The temp gauge on the dash is stuck at 0. Does it feed from the same temp sensor, or does it have 3 sensors like the B2230ft?

--
1990 740 Turbo, on its way to stock specs, maybe beyond

It's running better (and rich) because the AMM is disconnected. I pointed out several posts back the the ECU defaults to fixed settings when there is no input from the AMM. It's called "limp home mode" and it's richness is probably masking a vacuum leak that's causing he rough idle.

Like the B230F/FT, the temp gauge sensor is in the head, under the #2 intake runner, while the (Engine) Coolant Temp sensor (ECT) for the FI is farther back, about under #3 runner, a PITA to access. Only 2 sensors, like the B230FT. Except the B230's ECT sensor has dual elements. One for FI and the other for Ignition. (BTW, the "ECU" you mentioned earlier, with a vacuum line attached is the Ignition CU, which is very reliable.)

The wire to the temp sensor is yellow with a push-on terminal. Maybe it needs cleaning or tightening. You can also check the wiring back to the gauge by disconnecting it at the sensor and measuring the voltage there with the key ON. It should be 10 (yes 10) volts.


--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

I found the airbox thermostat failed in the hot-only position.

I also found the airbox flapper can be ripped out of the mechanism and stuffed into the hot-side intake. It makes a pretty good plug, even without any sealant. I don't think I could get it back out without breaking it.

--
1990 740 Turbo, on its way to stock specs, maybe beyond