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IAC clean; still won't idle 700 1989

The idle of my 89 740 GLE (16v, Bosch) is so bad now it doesn't even try to run.

Symptom: I turn the key to pos. II. Fuel pump runs for ~2sec. Turn to "Start". Engine starts on the first crank, every time. I release the starter. engine revs to ~1600-1800. Settles down to ~700. Seems to try to increace RPMs, tach drops and engine dies. Whole sequence takes about eight sec.

Done: Cleaned TB and passages, used old gasket, guessed the torque (snug plus a little). Cleaned IAC (twice!) with carb cleaner and air gun. cleaned IAC hoses and fittings. Checked Air Filter: pristine. New spark plugs: NGK perfect gap.

Thoughts: I wish I could find one of those old school mechs. The kind that sits outside thier "service stations" and listen to the cars driving by: "That one got a misfire, #2 I'd say." or "If that was my car I would retard the timing so much." One of these guys could at least tell me what I'm looking for. It seems no matter how it gets there, an engine either gets what it needs or doesn't and I don't have the experience to tell what mine isn't getting (or getting too much of).

Next step: I'm going to do the OBDI self diagnostic procedure from the FAQ to check some of the sensors.

Any ideas?

Aubrey








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IAC clean; still won't idle 700 1989

Have you checked the throttle position switch, it signals the IAC to take over idle control.
--
David Hunter








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IAC clean; still won't idle 700 1989

yes, the switch clicks just as i lift the lever, and clicks just before it closes.








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IAC clean; still won't idle 700 1989

Maybe you should do an ohmmeter check of the TPS switch at the ECU; it is possible for the TPS to click yet the contacts don't close correctly.

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








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IAC clean; still won't idle 700 1989

Does it start every time you turn the key?
--
90 744ti, Airbox, K/N, Cold air, G-Valve, Dual boost control, VDO, Modified exhaust. 88 745 gle, 99 Camry








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IAC clean; still won't idle 700 1989

yup, every turn of the key, and on the first crank.








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IAC clean; still won't idle 700 1989

You might try increasing the Air Bypass (Black) Screw on the Throttle Body -- I believe that counter clockwise increases air. Also, ground the IAC. Then see if it starts and maintains an idle. If so, after it's warm, adjust the base idle to about 725 rpm. Remove the IAC ground, and the idle should rise and sit in neutral at about 750 rpm or so.
--
dnvolvo '89 765T 200K - '91 245 100K








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IAC clean; still won't idle 700 1989

If the tach drops instantly, you've got an ignition problem.








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IAC clean; still won't idle 700 1989

This is a longshot but perhaps it's the main fuel pump. There is a tank pump that can partially pressurize the system but can't maintain it.

When my main pump went out a few years ago it behaved in a similar fashion.


--
Carter







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