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Vacuum question (Rough Idle)

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 90BlazerK5, Dec 15, 2001.

  1. 90BlazerK5

    90BlazerK5 Registered Member

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    Allright guys, heres the situation. Lately, I've been having a problem with a surging idle in my '90 K5. Its got hte stock 350 engine with TBI. Well, last night I got in there with some lights and started poking around, and I found something thats busted, but I'm not sure what it is, or what it does. its a short adjustable rod that comes off the side of the throttle linkage. It *looks* like the rod would attach to a black rubber vacuum diaphram located nearly straight back against the firewall. The metal clip on this diaphram is broken out, and the rod had dropped down onto the block, so I didn't see it at first. Now, what does this rod do??? Something to do with the cruise control system (which doesn't work), or could it be part of the cuase of the surging idle. The idle by the way, only gets bad once the engine warms up.....

    Where did all these damned dirty apes come from!?!
     
  2. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    Re: Vacuum question (I think)

    Without seeing it (my disclaimer clause [​IMG]) I would guess that that is the cruise. Should not adversely affect your idle...

    <font color=red>GOT MUD???</font color=red>
    My license plate reads:<font color=blue> 8 YR SUV</font color=blue>
    454/TH400/NP205 - 14BFF/D60/w/ 4.10s - 36" TSLs
     
  3. pr1aw

    pr1aw 1/2 ton status

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    Re: Vacuum question (I think)

    Same problem with my 91, haven't figured it out yet though.
     
  4. pr1aw

    pr1aw 1/2 ton status

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    Re: Vacuum question (I think)

    Is yours worse when the brakes are applied? I did a vaccum check and running almost 22 inches. With the brakes applied 21.
     
  5. Thunder

    Thunder 3/4 ton status

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    Re: Vacuum question (I think)

    You need to put a code scanner on it. That should show the problem
    Could be your coolant temp sensor which would give a code 15
    Or the Idle Air control system which will give a code 35

    If the idle is also rough it may be the O2 sensor or the EGR valve

    The rod you are talking about is part of the cruise control system. It should not be causing the surging idle.

    <P ID="edit"><FONT class="small">Edited by Thunder on 12/15/01 02:08 PM.</FONT></P>
     
  6. 90BlazerK5

    90BlazerK5 Registered Member

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    Re: Vacuum question (I think)

    Well, the code scanner didn't come back with anything. The roughness is about the same in both park and in drive (with brakes applied). I've got a new O2 sensor in it, so I don't think that is causing the problem. I'm going to clean out the EGR valve tomarrow, and replace the Idle Air Control valve. Hopefully that'll do the trick! [​IMG]
    Hooked the cruise control rod back up, only to discover that I've got a bad turn signal/cruise lever! [​IMG] Heck though, for as much as I use the cruise control, it can wait!! I'll let everyone know tomarrow hopefully if I got the idle back to normal. I appreciate the ideas! Keep 'em coming!

    Where did all these damned dirty apes come from!?!
     
  7. 90BlazerK5

    90BlazerK5 Registered Member

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    Okay, got in there today, and replaced the EGR valve. The idle has quieted down a WHOLE lot... still a little rough, but it doesn't drop the 400 rpm's that it was before.. now it stays in the 750-850 range. The valve itself looked pretty toasted, and htere was no gasket sitting underneath it. Also replaced the TPS at hte same time, so maybe that has something to do with it too. I've got the Idle Air Control sensor, and I'll pop that in tomarrow. But at least my idle is sitting about right again! Allright, next step- new alternator.... [​IMG]

    Where did all these damned dirty apes come from!?!
     

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