93 jgc 4.0 running rough

Agree with cleaning IAC and TB. Was the CPS that you changed OEM? Non OEM components seem to fail early. Some right out of the box are bad.

Plug doesn't look bad is it gapped correctly? 0.035




Regards,
JPNinPA

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Gap .035 on plugs
cps is oem replacement
Throttle body is clean

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The reason I was asking my 88 went from 20mpg to about 15 . After an incorrect thermostat was installed (180) witch caused the computer to sense a cold engine and keep the o2 sensor in open loop. This caused extra fuel that overloaded the cat ,causing it to overheat and plug up. It only took a month or so. Even though your cat is new don't overlook it.

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15 is low for an early gc, we got 19 with ours, normally. I wonder what is causing the problem. you got all the normal suspects
 

The gc has had a avarage of 15.8 since day i got it and i reset avarage every month to make sure it dose not drop but really hopeing it goes up lol

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I will check that next after a 30m drive to work with a patched exaust manifold the idel dose not drop below 500 rpm now so going to replace that but still idels rough glad that problem solved and just had a compression test done by a macanic and he said compression is good in all 6 cyclenders

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Not going to bother with maybe a bad o2 sensor i will just get it with exhust manifold and install both at same time to take out the guess work

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Look in the engine bay in the dark with engine running, look for spark.
Sounds like a coil or distributer cap.
 

Coil wires roter and cap all new 3 months ago no sparking and engine sounds healthy just rough idel once i accelerate its smooth ride

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What about a bad or clogged/dirty injector?

Have you ever run the process to clean the valves or combustion chamber? Water or seafoam?

Fuel pressure?

Air cleaner?


JPNinPA
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Last edited:
I will be running seafoam as soon as i am done putting new exhaust manifold on in process of doing now have tryed water but did no goo it seems or they were just worse than they are now exhaust manifold was cracked in 2 places and a couple of injectors were gummed up in intake manifold and i suspect was the rough idel problem but will find out tomorrow when its all put back together

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If this solves my problem will be very happy also took a look at carb and made sure was as close to spotless as can be since intake manifold is off and easly accessible

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If you have to replace any injectors go with the ones that have 4 spray holes. I got mine from Pic & Pull ( out of a couple of Neons)yours might have a different injector plug

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