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post #1 of (permalink) Old 01-08-2002, 01:46 PM
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Help 89 YJ rough idling?

My YJ is idling a little rough, not so bad that I can't stand it but enough so that it's noticible and my radio and anttena shakes. any ideas to fix this are apreciated, current idle is about 980 or so but allways under 10k is this too high? Some people have said that maybe my jeep is running rich, how do I fix that on a TBI engine?

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post #2 of (permalink) Old 01-08-2002, 03:19 PM
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Re:Help! Help 89 YJ rough idling?

Some one please help.

post #3 of (permalink) Old 01-08-2002, 04:37 PM
 
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Re: Help 89 YJ rough idling?

You may need to replace some sensors. Boston Mangler had similar problems and replacing several sensors helped. He also has a 89 with a tbi. If you do a search on his posts you will probably find the thread. It was a while ago.
Don't let it go too long because if you are running rich you will plug up your cat and will have to replace that too.

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post #4 of (permalink) Old 01-08-2002, 05:02 PM
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Re: Help 89 YJ rough idling?

I'd like to help, but first:

1. Complete your profile... it's nice to know specifics abuot you and the Jeep. We don't bie too bady around here.
2. Under what conditions does the Jeep idle rough?
3. If it's only at idle... I'd be looking at the Idle Air Control motor (IAC).
4. Do you have a manual on the Jeep?
5. Do you understand how EFI works?
6. Does it idle rough when cold as well as warm?

Let's start there....

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post #5 of (permalink) Old 01-08-2002, 05:16 PM
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Re: Help 89 YJ rough idling?

Did my profile, sorry I just singend up today! Anyhow, it idles rough right away and about 70% of the time. Now that I think about it though, I did just by pass the air box the other day with a K&N air filter cone at the end of the air tube. It may have strted doing this prior to my mod though
Were do I find the (IAC)? My jeep is a 4 cylinder 5 speed. I know very basics of EFI but as I understand it my engine is a TBI not EFI, their is a diference right? Idles a little better warm. Oh and again is close to 10K idle ok (allways under but close)?


post #6 of (permalink) Old 01-08-2002, 05:53 PM
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Re: Help 89 YJ rough idling?

EFI stands for Electronic Fuel Injection. TBI (Throttle Body Injection) is one form of EFI, as is SMPI, MPI, etc. All Germans shepards are dogs, not all dogs are German sheapards.

1. If it idles poorly when cold, then you can rule out most of the EFI sensors. They don't kick into the mix until the engine warms up to about 135*F and tell the computer to start leaning out the fuel mix. It's like a choke on a carb, you enrich the mix till the engine starts and lean it out as it warms up.
2. I thik you mean 1k (1000rpms), right? This is a very high idle for the engine, with a 5 spd it should be closer to 750rpm. Does the RMP climb as it warms or have you manually jacked up the RPM?
3. The K&N Filter should give it better breathing. The O2 sensor still is able to work with the better breathing. I don't think that's an issue. If you feel it is, take the filter off and let it breath freely. If the filter is choking down the engine then you should notice a difference.
4. I'd be more inclined to think the problem was one of a common tune up like Plugs, Wires, Cap and Rotor, etc.
5. Have you pulled the plugs to see what they look like? Anything out of the ordinary such as deposits, etc. on it?

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post #7 of (permalink) Old 01-09-2002, 12:07 PM
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Re: Help 89 YJ rough idling?

1st off thank you for your reply! I did some cold to warm testing on my jeep, i found that the rough idle doesnt happen till it reaches about 120 F. My temp hardly ever go's above that here in California even in the summer ( i think that in it self is strange) I did do a plug change on my jeep about 5 months(some deposits) so maybe it's time for an whole tune up like you said (cap, wires rotor, the works). I will do it this weekend. I have never touched the idle my self, but I will try to lower it just a tad over the weekend see how it runs around 750 as you recomended. I will update you on my test next Monday, thanks for all the help.

post #8 of (permalink) Old 01-09-2002, 12:39 PM
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Re: Help 89 YJ rough idling?

LEVE, doesn't the temp sender tell the 'puter how much choke to use?? Most of the systems that I've worked with (all earlier GM's) want the temp to get to 190-210 before completely turning off the choke. Maybe he's not getting hot enough and running rich?? Just my .02.

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post #9 of (permalink) Old 01-09-2002, 12:42 PM
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Re: Help 89 YJ rough idling?

Everyone (not mechanics) I have spoken to says that my engine runs cool (according to them that better then running hot), and the Mechanics have said for a fact that my engine runs rich (this is why I had to replace my cat and muf recently) however becouse they were a muffler shop they didnt know how to fix the source of the problem.

post #10 of (permalink) Old 01-09-2002, 01:02 PM
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Re: Help 89 YJ rough idling?

1. If your engine temp never goes over 120*F... this is a MAJOR problem. The compueter never sees the temp come up and then never goes to closed loop. Open loop is always used and this is always a rich mixture.
2. Lower the idle, if you can, on some EFI engines it's not recommended or it is not possible.
3. Start putting EVERYTHNG you can back to OEM Specifications. You'd be surprised how much fiddeling a PO can do and get stuff outta whack.
4. Do the Tune-up, plugs and wires, cap an rotor. It's not good money after bad, it's so you know what's good and what's not.
5. 79XCABChevy, On the Earlier EFI's the computer trips to Closed Loop when the engine is at a minimum temp. Choking is done when the O2 sensor comes into play and starts to regulate the mix... so as you can see it's not really choking, it's regulating the mix. At this temp the O2 sensor can still richen or lean the mixture to affect the ratio.
6. 79XCABChevy & bigrubberjeep... Good Call! You're both correct that the engine's running too cool. The 195*f - 208*f is optimal. Now's a good time to check to see if the thermostat is stuck open.

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