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Looking for help "hunting idle" at cold start "surging idle" at warm start

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muscam1
Posts: 10
Joined: Tue Dec 30, 2014 8:26 pm
Location: Edmond Ok

Looking for help "hunting idle" at cold start "surging idle" at warm start

Post by muscam1 » Fri Jan 11, 2019 11:28 pm

I’m helping a friend resolve a cold and warm start issue and would appreciate any guidance. It’s a 1983 633 with about 80k miles. He recently purchased it from a consignment dealer and initially thought he had some bad gas because the car sat for a while.

On cold start – it stalls out on the first two attempts to start, and on the third it “hunts for an idle” until the car warms up. Once warmed up the idle starts to surge from low to high.

From a warm start it goes immediately to the surging idle condition.

We have cleaned and tested the Idle Control Valve. The ohms testing was about 10 ohms. When turning the ignition key to the first positon (valve is already in the open position) you hear a click from the control valve, but I don’t see the valve vibrating like some articles say you should see.

We have replaced the ICV control unit that’s in the glove box with what is reported to be a working unit, but there is no change in the idle situation either at cold start or warm start.

The interesting thing is that before we “cleaned” the ICV, when the engine was warm we did not have the idle surging condition and it would idle around 1100 rpm – so we caused the surging somehow after the ICV cleaning. We cleaned the ICV with carburetor spray cleaner. The other interesting thing is that from a warm start with the surging idle, if I remove the dipstick – the surging ends and the rpms are steady around 1300 rpm. Normally, you would expect the reverse when you remove the dipstick resulting in an engine that sounds like it’s about to stall.

Any thoughts or guidance would be appreciated

Thanks--Marc

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Brucey
6 Series Guru
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Location: Cambridge, UK

Re: Looking for help "hunting idle" at cold start "surging idle" at warm start

Post by Brucey » Sat Jan 12, 2019 1:11 pm

you need to reset the throttle body and then the TPS, as per the manual, in that order.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

muscam1
Posts: 10
Joined: Tue Dec 30, 2014 8:26 pm
Location: Edmond Ok

Re: Looking for help "hunting idle" at cold start "surging idle" at warm start

Post by muscam1 » Sat Jan 12, 2019 8:25 pm

Thanks Brucey we will try that and get back to the board.

--Marc

muscam1
Posts: 10
Joined: Tue Dec 30, 2014 8:26 pm
Location: Edmond Ok

Re: Looking for help "hunting idle" at cold start "surging idle" at warm start

Post by muscam1 » Wed Jan 16, 2019 2:37 am

Update:

We have reset the throttle body butterfly flap to .015in (was a little too tight against the throttle body) and the TPS per the manual. We originally thought we had a bad TPS but upon further testing we get the correct continuity results per the manual for at closed throttle, partially opened, and fully opened. We also confirmed we have 5v coming from the harness connector.

Car has the same symptoms - hunting idle at cold start and surging up and down at warm start.

Would appreciate ideas on what to look at next

Thanks - Marc

wvcsi
Posts: 1
Joined: Wed Jan 16, 2019 4:17 pm
Location: West Virginia

Re: Looking for help "hunting idle" at cold start "surging idle" at warm start

Post by wvcsi » Wed Jan 16, 2019 4:22 pm

To clarify, we have reset the throttle body butterfly flap to approximately .0015 in (per page 7- 21 Bently Service Manual).

muscam1
Posts: 10
Joined: Tue Dec 30, 2014 8:26 pm
Location: Edmond Ok

Re: Looking for help "hunting idle" at cold start "surging idle" at warm start

Post by muscam1 » Wed Jan 16, 2019 4:43 pm

Thanks for fixing my missing zero :)

WVCSI is my friend whom I'm "trying" to help. Good that he's joined this board so he can provide direct input!

--Marc

muscam1
Posts: 10
Joined: Tue Dec 30, 2014 8:26 pm
Location: Edmond Ok

Re: Looking for help "hunting idle" at cold start "surging idle" at warm start

Post by muscam1 » Thu Jan 24, 2019 1:33 pm

We're kind of stuck at this point and prefer not to "throw" parts at it. Anybody have ideas on next diagnostic/resolution steps?

Thanks--Marc

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