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Question weird surging lately...

Hi all, long time no talkie

I'm having a problem with some surging at idle. I've searched the forum and found MANY threads on the subject, but none are quite like the problem I'm having. A few months ago, I noticed that after my car warmed up for a bit, it would start to surge at idle. It drops to about 250 rpms and goes up around 1500 rpms. It would do this if it was a somewhat warm day (maybe in the 40's or 50's), but in colder weather, it seems to idle fine. This morning (in the 50's) I cant seem to keep it running and it just stalls out. I havent run any Techron thru it in awhile, so I'm going to do that first. The funny thing is that when it's cold it starts and idles great, then it behaves weird for awhile and usually is fine after that. Somtimes it will surge, then work great within a minute, then start to surge again. I dont have fuel pressure gauges, but is there any other relays and voltages I can check to narrow down the possible problem here?

Thanks for the help guys!

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'82 911SC Targa!
Old 01-19-2005, 10:17 AM
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surging usually means too rich. the frequency valve may not be getting activated by the oxy sensor computer. the oxy computer relay may be bad, or lacking 12V from the same fuse as the dome light. temporarily unplug the relay or remove the fuse, and see if the idle drops off and the engine runs rougher. the relay is under the front of the right seat, toward the tunnel.
or it may simply be adjusted too rich.
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Last edited by john walker's workshop; 01-19-2005 at 11:03 AM..
Old 01-19-2005, 11:01 AM
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Thanks John,
I disconnected the o2 sensor about a year ago and adjusted the mixture accordingly. I dont recall the what I set it at, but it was the "standard" disconnected setting for SCs. Do you think I should buy another o2 sensor and hook it up? It's run very well up until this point (and thru last winter), could the mixture just change on its own?
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Old 01-19-2005, 12:56 PM
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first check the frequency valve to be sure it's working.
the mix can change somewhat between hot summer and cold winter. the warmup reg is affected by temperature.
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Old 01-19-2005, 01:33 PM
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super, thanks JW!
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Old 01-19-2005, 01:45 PM
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I had a similar problem in my 84. It was the mixture.
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Old 01-19-2005, 10:01 PM
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Yep, I checked out my mixture this weekend and, WOW, it was about 9! That's weird because Pat and I set it about a year ago to 3. I have not had an o2 sensor, so I bought one from our host and set the co to ~1.5, then hooked up the o2 sensor. Man, it is running very nicely now and not a single sign of surging. You guys rock, funny how simple something like that can be

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Old 02-08-2005, 07:22 PM
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