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I am really perplexed - help! 700 1991

posted by darius on Tue Oct 7 13:06 CST 2003
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last visit: Sat Sep 20 19:24 CST 2014

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I have been on a wild goose chase to try to figure out why my car's (745 Turbo, 162k miles)idle is too low (around 600 under load, 700-750 in Park or Neutral), and when the idle is low and car fully warmed up, the oil pressure light goes on. Maybe some of you have read my many previous posts trying to solve this annoying problem. I would really love some help solving this as it I have become somewhat obsessed with it. BTW the car never stalls.

I have replaced (or had replaced)
--02 sensor
--coolant temp sensor
--throttle position switch (yes, it is correctly adjusted)
--rpm sensor (replaced by seller when I purchased car in Arpil 03)
--Idle Air Control valve
--fuel pressure regulator
--throttle body cleaned
--vacuum hoses checked (no leaks, all clear)
--crankcase checked for negative pressure (good)
--oil breather box checked (it is open,oil pours down into it easily)
--clamped off the hose to the idle air valve and it caused the idle to drop to about 300 (didn't stall till I removed the plastic clamp), which means the IAC is working

None of these attempts to fix the problem has worked, though the idle in Park and Neutral seems closer to normal than it did (around 750). But under load, in Drive or Reverse, and with the a/c on, the idle dips to 500 then recovers to 600.

I am at the point where I am ready to take the car to the local Volvo dealer to have them work their magic and diagnose this very persistent problem. The guy who runs the service dept is very helpful but suggested I just live with this until (and if) it gets worse. (BTW, oil pressure is fine at idle, it was checked by my indy mechanic.)

If anyone has any ideas about what might work, I would deeply appreciate the help.

Thanks everyone.
--
Darius in Albany NY '86 744 GLE (172K); '91 745T (161K)

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I am really perplexed - help! 700 1991

posted by someone claiming to be ringlee on Wed Oct 8 01:53 CST 2003 [RELATED]

I would follow John's advice and use the stop screw to slightly open the butterfly valve, then readjust the TPS to idle at that point. If you take it to the dealer, they will try to sell you a new ECU.

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I am really perplexed - help! 700 1991

posted by bagle on Tue Oct 7 22:54 CST 2003
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last visit: Sun Oct 28 00:26 CST 2001

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John's suggestion might solve your problem. Some other things to check/do are
Check the ignition timing; Too retarded and it might idle slower. Clean all the ground connections. This is good PM anyway.(the FAQ has an excellent part on this)If you have access to another ECU, you could try swapping it in to see if that fixes it.
Good luck
--
bagle 87 745t

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I am really perplexed - help! 700 1991

posted by someone claiming to be ringlee on Wed Oct 8 01:56 CST 2003 [RELATED]

Timing check is a good suggestion: one notch off on the belt installation and you've got a problem.

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I am really perplexed - help! 700 1991

posted by darius on Wed Oct 8 01:48 CST 2003
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last visit: Sat Sep 20 19:24 CST 2014

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the only other ecu I have access to is the one in my '86 744 non turbo, so do you have any suggestions for where I might find one to try?
--
Darius in Albany NY '86 744 GLE (172K); '91 745T (161K)

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I am really perplexed - help! 700 1991

posted by someone claiming to be muchostupido on Tue Oct 7 15:20 CST 2003 [RELATED]

I think I replied already to your last post 6 weeks ago.
My idea is the brakebooster.
I had that problem and posted it in February/March 2003.
To check it out, apply the brakes and check if the idle changes.

My car is 86 NA, don't know about the 91 model.
Basicaly it could be possible, that your brakebooster is leaking
always air in, when you are in idle and don't apply brake.
Then you engage in D and apply brakes and close the airleak.
Check it out.

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I am really perplexed - help! 700 1991

posted by darius on Tue Oct 7 15:34 CST 2003
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last visit: Sat Sep 20 19:24 CST 2014

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Thanks for the suggestion; I remember it from before, and there is no change in idle when I apply the brakes. I tried it several times to see and found no effect. Thanks.
--
Darius in Albany NY '86 744 GLE (172K); '91 745T (161K)

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I am really perplexed - help! 700 1991

posted by john sargent on Tue Oct 7 13:28 CST 2003
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last visit: Wed Oct 22 09:07 CST 2014

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You probably have a tired IAC. You can help it out by very slightly opening the butterfly valve with the throttle stop screw. If you do this, be sure to re-adjust the throttle position switch. Your hot idle speed may elecate slightly.

As to the oil pressure light, I would install a mechanical gauge and check the oil pressure. The Volvo red engines can push the seals on the oil delivery tube over the ridges on the tube, and the oil pressure will then run low. I have seen that several times.

Although the attached picture is a little dark, you can see the seal pushed out of position on this oil delivery tube. This engine had a little over 106,000 miles.

--
john

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I am really perplexed - help! 700 1991

posted by darius on Tue Oct 7 14:58 CST 2003
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last visit: Sat Sep 20 19:24 CST 2014

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Thanks for the ideas, John. I will pursue the oil delivery tube seal issue - where is the oil delivery tube? Is it accessible only by taking the oil pan off?

My IAC is brand-new from the Volvo dealer; just got it about six weeks ago. I doubt it is tired yet. I was hoping that replacement might solve the problem and was very disappointed that my investment of $140 didn't pay off.

Thanks again.
--
Darius in Albany NY '86 744 GLE (172K); '91 745T (161K)

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I am really perplexed - help! 700 1991

posted by john sargent on Tue Oct 7 16:31 CST 2003
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last visit: Wed Oct 22 09:07 CST 2014

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Yes, the oil delivery tube is accessed only after removing the oil pan.

Check the oil pressure before you proceed in that direction. The 700/900 FAQ have excellent instructions by Dick Reiss on this task.
--
john

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