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high idle when raining
Topic Started: Dec 7 2016, 09:17 AM (296 Views)
skydivemark
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'95 metro 3cyl, 1L , manual, 316K miles. When it rains the engine idles very high when I first start it - 2200+ rpm and when the A/C compressor kicks off it idles so high the rev limiter kicks in and it surges/oscillates from 2200-3500rpm. But the weirder part is after it warms up (5-10 minutes of running) if I shut it off and re-start it, it runs normal.
Has anyone else experienced anything like this.
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LesCrapp
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Legend

ISC you will have to do a little research on here but there is a procedure using a feeler gauge between the throttle stop screw (.014) or something sorry can't remember but maybe this will help you on your cure...


P.S. you will have to make sure you have the upgraded emissions the ISC it is black plastic box on the back of the throttle body with a white plunger that touches and pushes on the throttle to increase idle speed.
Edited by LesCrapp, Dec 7 2016, 10:26 AM.
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Metromightymouse
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Powdercoat Wizard

All 95s have the ISC.
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LesCrapp
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Legend

?
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myredvert
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myredvert

The first thing I would do is observe the Idle Speed control (ISC) motor and see if it is driving the idle speed changes or reacting to them, then observe its behavior again after you do the "warm up and shut it off then restart" thing and it goes away.

Since you say this only happens when its raining, I would consider spraying both the TPS and ISC with some type of electrical parts cleaner or wire dryer and see if that makes a difference.

If the ISC is driving the idle fluctuations, check the TPS adjustment by carefully following the actual Factory Service Manual instructions. For your 95 you can still use the procedure for checking the TPS adjustment in the 1994 FSM in the forum library.

The fact that it instantly changes behavior after you shut it off when its warm doesn't seem to suggest a vacuum leak, but a very careful check of all vacuum lines or better yet a complete replacement if their age is unknown can't hurt to eliminate that one possibility.

Are you getting actual rpm values from a tachometer?

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Metromightymouse
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LesCrapp
Dec 8 2016, 09:58 PM
?
94s potentially have an IAC (idle air control) or an ISC (idle speed control) with upgraded emissions. If you have a 95 it has the ISC, no upgraded emissions to check for.
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skydivemark
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Sorry for slow response. It is a 95, and hasn't acted up lately due to nicer weather so troubleshooting an intermittent problem (as you know) can be challenging (and low priority when not acting up). It does seem to be ISC related because lately it (sometimes) doesn't kick-up the idle rpm when the a/c compressor comes on.
It is the black box with the white plunger. I think on my days off I'll take the connector off and clean the plug contacts with electro contact cleaner (LPS brand) and see if that helps.
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skydivemark
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Update:
Been cold here last few days (cold for Florida) and the choke portion of the ISC seems to be working fine.
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