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Old 09-01-2017, 10:04 PM   #1
lummert
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Default Idle speed

My 88 765 with B230FT and LH2.2 idles fine at startup (cold or warm). After getting to my destination (short or long distance) it idles higher than 1000 rpm after putting the trans in park. Always idles fine in drive. Just wondering if this is related to TPS or if it's related to IAC. When leaving the car idle after shifting to park the idle will eventually return to normal.
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Last edited by lummert; 09-04-2017 at 08:49 PM..
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Old 09-04-2017, 12:05 AM   #2
84B23F
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Try cleaning AMM first, with new air filter
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Old 09-08-2017, 02:31 PM   #3
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May have found the cause of the idle problem. There is a vacuum T with check valves coming off the intake manifold running towards the exhaust side of the engine. I'd been finding one of the hoses disconnected, but was thinking that I had knocked it loose messing with things. Yesterday I raised the hood and found the same hose had come loose again.

I used 3/8" and 3/16" gas hose to make repairs. Shoving the 3/16" hose into one end of the 3/8" hose took care of the hoses that were 3/8" ID on one end and 3/16" ID on the other.
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Old 09-11-2017, 02:50 AM   #4
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Wondered about vacuum.

* On my LH 2.2 set up the IAC was funky, cleaning made almost no difference. Finally found another one at a bone yard, now it's about normal (a little higher idle cold start, & drops down after warm up).
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Old 09-13-2017, 01:45 PM   #5
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Idle speed problem is fixed. Switching from a 88C to 82C thermostat also lowered the idle speed a bit back to a normal idle. Didn't know that the coolant temp could effect the idle speed in this way.

So yes: vacuum leaks and coolant temp.
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Old 09-13-2017, 01:48 PM   #6
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Dammit Lummert. Vacuum leak check is always #1
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Old 09-13-2017, 01:49 PM   #7
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Quote:
Originally Posted by 84B23F View Post
Try cleaning AMM first, with new air filter
Air filter only a year old and I don't live in a dusty climate. Filter stays clean a fairly long time. I've not needed to clean the AMM since I've own the car (12 years), but the engine has blowby which may be getting oil in the AMM.
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Old 09-14-2017, 01:13 AM   #8
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Quote:
Originally Posted by lummert View Post
Switching from a 88C to 82C thermostat...lowered the idle speed
I would have reservations about that conclusion...

RE: clean the AMM

There is a self cleaning cycle...but I'd venture to say those thermal cycles affects wire's sensitivity, with time.

Whoever did the programming determined what's happening. Thermal wire detects slower air flow, so IAC kicks in...could have been programmed.... On LH 2.4, faulty AMM caused higher idle revs.. Since new AMM corrected idle RPM, I concluded Bosch's programmer(s) did not examine actual RPM.

On Lh 2.2 (or whatever came with 1984-B23F), defective AMM caused loping-variations in RPM, and at a higher rpm, iirc.
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