Rough cold idle in 258 - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 09-11-2000, 02:16 PM Thread Starter
 
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Rough cold idle in 258

My yj has a 4.2 258 with the carter 2 barrel carb. I have only had this vehical for 3 months but I have noticed that the damned thing will not idle worth @#$% when you fist start it up in the morning and when you start it up to go home after work. At work it sits at the shop for about 8 hours so the engine is cold. I thought it could be the usual culprit, the clogged idle tubes, but if this were true wouldn't it do it all the time at idle. The engine idles fine after it's been warmed up. I really want to fix this before winter sets in because I live in saskatchewan and -40 C is not an uncommon temp to wake up to and I know that jeep will not start, it'll sit there and fart and belch and die. I checked the idle tubes and their not dripping fuel at idle and they give off two even streams of fuel when you gun it. It's not the egr valve or the choke, I checked them both. If I had a vacuum leak it would idle bad all the time. The stepper motor works fine. So I am thinking that it might be the evaperation canister purging at idle(I havent ckecked this yet). But I was wondering if their is a test for the thermal electric switch in the air cleaner housing, because if that was buggered up the computer would never know the outside temperature and wouldn't adjust the fuel mixture for a cold start-up condition. If anybody know of anything else I would very much appreciate you advice. The think that is strange is some of the usual problems dont apply because its only crappy when its cold.

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post #2 of (permalink) Old 09-11-2000, 06:29 PM
sas87yj
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Re: Rough cold idle in 258

you seem to be on top of the possibilities![img]/wwwthreads_images/icons/smile.gif[/img]

i had similar probs with mine and i replaced egr, cto valve, temp sensor, vacuum lines and eventually new rebuilt carter by holly. not until the new carb did it finally run right. it runs great now!

seems like you have posted on this subject before? i can't remember.

bet you have this tech page by the sounds of your knowledge:

http://www.off-road.com/jeep/tech/engine/carter.html

and:

http://www.off-road.com/jeep/tech/258bbd/Major.htm
post #3 of (permalink) Old 09-11-2000, 08:33 PM
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Re: Rough cold idle in 258

Need the carb replaced or the bottom shaved and trued carborator plates in severe weather tend to warp. not to mention that it is a carter 2bbl were in one can be the best carb ever and 10 suck. Lots of people say "it cant warp its cast" i say horse pucky seen it only explanation we could find on a costumers jeep. put the carb on the glass shelf in the parts department and it rocked back and forth on two bolt inlets. have seen that more often than not lately. Also could be as simple as a gasket. yes your rough idle would be all the time in that case. Could have been a carb just on the border line of passing specs. Test the choke and another tip on the carters bring your rpm up to 2200 or so and takk a rag and with your hands smother the carb till its about to choke out if it chokes out then vacuum in nominal or average. I have jeep eagle 4x4 that is the same power plant and had the same problem i got a new carb. Test the thermal electric switch with an ordinary lighter and a test light or continuity tester if the juice is flowing at dead cold start note this then with the tester still in place hit it with the lighter and see if she shuts down. Somthin silly but should mention it make sure if you have an electric or thermal choke : electric check it with the tester to prove power : thermal is the same lighter or soldering iron scinario
goodluck

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post #4 of (permalink) Old 09-11-2000, 10:26 PM
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Re: Rough cold idle in 258

It sounds like a bad choke pull-off to me. It's a vacuum diaphram that opens the choke a little once the engine starts running. They're about $15 at NPA.

jerry

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post #5 of (permalink) Old 09-12-2000, 11:18 AM
 
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Re: Rough cold idle in 258

I have a similar problem on my 258. Someone who checked it out told me that my choke was not operating at all. How exactly do I fix this? Could it be the choke pull-off, as you mentioned?

Thanks

Sean

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post #6 of (permalink) Old 09-12-2000, 09:49 PM
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Re: Rough cold idle in 258

If your choke isn't working, it's usually either binding linkage or a bad choke. If it's the linkage, it probably just needs cleaned with carburator cleaner. If it's a bad choke, it needs replaced and if it's the original choke, it's probably riveted on. There's a pretty good section on the carburator (Carter BBD) somewhere in the jeep tech section of off-road.com that might help you determine the problem.

jerry

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