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94 running rough


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At low idle it's running rough then after a few minutes it will eventionally die... but at about 1800rpm and running dow the road it runs fine. New fuel filter, air filter, plugs,wire, distributors cap rotor clean the mass air flow sensor clean the screen out check for vacuum leaks can't find any that I'm aware of. Thinkin o2 sensor next but thought I'd see if any advise

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That is strange... Are there any fault codes stored in the ECU?

 

B

 

Also, I deleted several duplicate threads you posted and duplicate posts in other threads. Please do not do that, it confuses the issue and is against the rules. If you do not desist, your account will be suspended.

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Mine was moisture related bit I suspect if yours is doing it all the time moisture may not make it any worse.. Mine would go back to normal once dried off but it was in fact bad. New coil, no issues since. Worth a shot if your out of options..

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If the exhaust is clogged it won't run well, if at all. The engine needs to spit out the exhaust. Unless your O2 is bad and dumping a lot of fuel into the exhaust, it's unlikely the cat is clogged. Possibly but unlikely.

 

The maf will probably check out fine. Add a ground to the existing ground. It drops it at random.

Edited by RF600
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I still doubt a clogged cat. Seems like it would run worse the higher it revved rather than sorting itself out around 1800 rpm like you said. If the cat's hot enough to glow, that suggests that there's a lot of unburned fuel in the exhaust, which the catalyst is burning (as it's supposed to). That kind of heat probably isn't good for it, but IMO it points to a problem other than the catalyst.

 

Normally I'd say it's got a misfire, so it's blowing unburned fuel/air right into the cat, but your recent tune-up and the fact that it runs alright at speed kind of shoots that down. It could be a sensor screwing with the mix (MAF, coolant temp, or O2). IIRC the ECU is supposed to be able to guess sensor values well enough to run without them, so you might try unplugging each in turn to see if it idles better guessing at values than it did listening to the sensors (which would indicate sensor or sensor wiring issues). The idle air control stuff does cause idle problems from time to time, but I've never heard of it making the cat glow.

My pet theory is that you have an injector or two that are leaking internally. This would show up most at idle, where very little air/fuel are going through the system, and any extra fuel is going to have a big effect on the ratio. At higher speeds, there's more air/fuel going through anyway, so the leak doesn't make as much difference. At idle, though, all that additional fuel won't burn properly, making for rich exhaust; the ECU will see this as a general rich condition (it only has one oxygen sensor) and lean out the mix; the other cylinders will run lean, contributing air to the exhaust; and the fuel will meet the air in the catalyst and burn like crazy. Meanwhile, your engine sputters and chokes and tries to run with a couple cylinders pig rich and the rest starving for fuel.

I would have a look at the spark plugs and see what they tell you. White crusty plugs are lean, dark or wet plugs are rich. Your new plugs might not have been in there long enough to tell you a whole lot, but it's the best way I can think of to track this down, assuming it is what I think it is.

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