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Rough Idle Question - Clarified 200 1981

posted by DougC on Thu Apr 10 03:05 CST 2003
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last visit: Sun Aug 10 08:30 CST 2014

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1981 K-Jet. I'm getting ready to go after the rough idle this car has. The car has a new intake manifold gasket, injector seals, cap and rotor, and throttle body gasket but it still idles roughly sometimes. When I first start it up, it hunts for a few seconds then smooths out ok. When it's warmed up, it will sometimes idle roughly. Under acceleration or deceleration, it's very smooth. The spark plugs are old but look fine to me. The wiring harness is old and showing signs of deterioration. When cold it will die at the first two stop signs if I put in the clutch fast. After two or three minutes running, it runs fine and stays running like it should. The car has no other problems with the way it runs. Everything works fine, except I'd like to smooth out the idle.

What are the most likely causes of a rough idle on this car? I'm not sure where to start.
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Thanks to everyone for the help, Doug C. 81 242 Brick Off Blocks, stock, M46; 86 240, 130K
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Thanks to everyone for the help, Doug C. 81 242 Brick Off Blocks, stock, M46; 86 240, 130K

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Rough Idle Question - Clarified 200 1981

posted by mcduck on Thu Apr 10 03:32 CST 2003
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last visit: Sun Sep 9 11:47 CST 2012

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I had a similar problem on my '78. Check that the frequency valve is buzzing. My problem was caused by the fuel pump relay, which also powers the Lambda system by pulling in the F.I. relay, having the usual cracked solder.
This caused the engine to run lean, which was good for gas mileage, but not so good for idle.

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Rough Idle Question - Clarified 200 1981

posted by rmagoo on Thu Apr 10 03:14 CST 2003
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did you check the spray pattern on your injectors when you had them out? did you clean them? old k-jet injectors are notorious for problems like this, also haveyou checked your fuel pressures. check control and line pressure, maybe you have a bad warm up regulator. some models have a series of vacuum hoses and a check valve on the warm up regulator that act as an accelerator pump when its cold if those hoses are cracked or the check valve is bad it also could cause this problem.

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Rough Idle Question - Clarified 200 1981

posted by DougC on Thu Apr 10 16:27 CST 2003
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last visit: Sun Aug 10 08:30 CST 2014

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Thanks. I'm not sure what order would make the most sense to check the things you mention. I haven't done much fuel system work. All I did so far under the hood to the fuel system is pull out the injectors, clean the ports, clean the outside of the injectors, clean the plastic retainers, install new seals, and reinstall. Also, I replaced the fuel filter. Any suggestions on a logical order to check the things you mention?
--
Thanks to everyone for the help, Doug C. 81 242 Brick Off Blocks, stock, M46; 86 240, 130K

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