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Thread: 87 2.0 rough idle after choke turns off

  1. #1

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    87 2.0 rough idle after choke turns off

    i cant seem to figure it, i ve replaced the cap, rotor, plugs, wires, oil changed and a new fuel filter. it starts up and idles fine then as soon as the choke turns off it runs like poop. i have been able to drive it and it has a hesitation at 2500-3k rpm. timing is around 10 BTDC but when i try to adjust at the distributer it runs worse and stalls out with to much advance. it seems to have be running rich form the black liquid coming out of the tail pipe but the plugs are black around the edges and white on the tip.

    2.0 carb 2wd 5 speed

  2. #2



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    #1: EGR valve is stuck open. Remove, clean, and stick back on. That's a good start.
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  3. #3

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    would the O2 sensor do this too?

  4. #4



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    That would cause it to run dirty but the rough is a sign of the EGR stuck open. Or the timing belt jumped a tooth. But that would normally make it not want to move out of it's own way.
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  5. #5

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    this might be a dumb question... where is the egr valve?

  6. #6



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  7. #7



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    On my 86 when I had the stock Mikuni carb, there was a EGR sub valve on the base of the carb. It is actuated by linkage on the carb. It is located on the drivers side of carb at the base and to remove it to clean you have to remove the "C" clip holding the linkage pin and linkage to the metal valve plunger. Remove the accordion rubber protection boot and move the small linkage arm out of the way and slide out the sub egr valve metal plunger from carb.
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    These metal plungers would get carboned up a lot and stick open. Mine would even make the gas pedal feel like a binding linkage problem when it got stuck. In fact the EGR system on these motors is like a carbon making farm and causes the system to get clogged with black soot. I'm sure when you check the EGR valve you will see the build up. This will continue the entire distance of the EGR gases and needs to be cleaned. SO, through the intake manifold into the head and dumping into an exhaust port. Usually a coat hanger or wire brush tip rod cleans them out pretty well.
    Your EGR should not be opening at idle and or WOT and your probably getting vacuum at these times and shouldn't.
    If EGR is on during idle, stumble and even stalling will likely result. If EGR is on during hard acceleration, low power (from reduced air/fuel volume) is the result. At part load, mix advanced for economy, conditions that create high combustion chamber temperatures. Without EGR, these conditions not only create [NO.sub.x], they foster pre-ignition and pinging.

    This is all for cleaner air to breath and making your truck engine eat it's own poo over again.

  8. #8

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    so i cleaned the egr and it was pretty bad and i changed the O2 sensor to bosch universal unit. it seems to running better but it still isnt idling very well after warm up. timing is way off around 15ish degrees BTDC bit there is room for advance. is my distributor off a tooth maybe or is there a vacuum line i should be unplugging or a terminal that should be jumped?

  9. #9



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    Check your cam timing to crank. I bet the belt is getting ready to break. 15 deg is about 1 tooth on the belt. The distributer can't jump a tooth it's not able to. The only way it can be off is by removing it and reinstalling it.
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  10. #10

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    i replaced the timing belt. and silent shaft belts pullys and adjusters. all my timing marks are on. i did remove the distributor at some point chasing a solution to the rough idle maybe i need to move it again to see if itll work.

  11. #11

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    is the cam timing mark directly at the 9 o'clock or is it just below?

  12. #12



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    The mark is just below the head line. Look on your head and see if you have the "BUMP" Clean off the old oil you will see it.



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  13. #13



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    I know when I pulled my distributor and reinstalled it. I thought I had it set to number 1 on compression stroke, but it was slightly before and one tooth off., that one tooth syndrome strikes again.

    While your timing it, pinch the vacuum line and see if it causes it to move off your mark. You will probably find the problem and kick yourself that you didn't find it sooner. It seems to happen here a lot. The distributor has a mark at the bottom of the unit. There is one on the distributor gear and it must line up with the one on the housing right near it. They are very tiny dot marks in the casting. Once you line these up, you have the job to insert the distributor without moving these two dots apart, otherwise you miss the drop. I would remove the cap and grab the dizzy top with the rotor and keep that rotor from trying to turn just before the dizzy makes it all the way in. It's kinda tricky and there is also a starting point for the dizzy that they placed on the head to line up with the mark on the distributor housing after it is installed. Mine kinda looks like it's one tooth after the number one electrode post on cap, but it's just the illusion. Felt pen the outer housing at number with a line helps to.

  14. #14

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    i didnt notice any marks on my distributor so now ill have to look again. thank you

  15. #15

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    so i re checked my cam timing and its right on i looked at the rotor on the distributor and it is right where the number one post is on the cap. it was a little hard to get running today and when i pinched the Dist. vacuum hose it died. im not really sure if thats the right reaction or not but im still stumped

    does anyone know what the factory settings are on the carb like the SAS 1,2,3 and throttle opener

  16. #16



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    There should be a mixture adjustment set screw on the drivers side of the carb. Its hidden behind a factory set plug that would need to be removed if you ever wanted to try a mixture change. I don't think I have ever seen anyone start doing mixture setting on one of these Mikuni carbs yet. These carbs are so crazy that if you make any changes at all you better document it because you will never return to it again on memory. These carbs are garbage also, as you will notice everyone that can make a swap to weber most certainly does. I don't know the Oregon laws, but in Washington my truck is exempt from smog test and I can do whatever I want to it now.
    Have you done a compression test? Wet & Dry. I don't see anything about one and it could remove a low compression rings problem or burnt valve.
    I don't think your truck should stall when you pinch the advance air line going to it from the carb. In fact I am pretty sure that the distributor does not begin advancing till throttle gets to a certain rpms. The manual could better explain this (see below).
    We have shop manuals here also and you can download one and go through diagnostics. They are also pretty much a requirement for these trucks if you don't have one you could throw money in the wrong direction.

    This link has a really good manual and you can download it all or sections.
    http://www.mightyram50.net/vbulletin...ory-manual-PDF

  17. #17

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    i live within the reaches of the portland metro area so i have to go threw deq. otherwise i already have a weber from my toyota so all i would need is an adapter plate.

    the mixture screw looks like someone has already messed with it. thats why i was hoping for the stock settings for the carb

    i havent done a compression test on it, i have to go buy a compression tester.

  18. #18

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    Does anyone have a vacuum diagram that actually shows where the hoses go. The one in the chiltons book isnt very accurate as well as the sticker under the hood

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