flint54 Posted November 14, 2011 Share Posted November 14, 2011 This one baffles me. When (and only when) the motor is running, the throttle feels like something is holding it closed. I have to step on it hard to overcome the resistance. The pedal freely pivots, the cable freely slides, and the throttle link and plate operate by hand freely. When the motor is not running, the pedal is smooth as silk. The throttle body is clean as new. I even disconnected the cruise cable to make certain that wasn't a factor. This just started a couple days ago on a road trip. Once the initial resistance is overcome, the throttle is smooth throughout the rest of the range of motion. It seems very improbable that manifold vacuum could cause this, particularly since it just started happening. Anyone have a clue what's going on? Link to comment Share on other sites More sharing options...
carnuck Posted November 14, 2011 Share Posted November 14, 2011 Sounds like the IAC is clogged Link to comment Share on other sites More sharing options...
Pete M Posted November 14, 2011 Share Posted November 14, 2011 my 90's throttle cable started pulling apart and this little sleeve of plastic on it was catching. sorry i can't be more specific, but I am now 750 miles from that cable and can't snap a photo 'til I get back home next week. Link to comment Share on other sites More sharing options...
flint54 Posted November 14, 2011 Author Share Posted November 14, 2011 The IAC was a good suggestion, even though it was new last year and my idle is perfectly smooth. To be certain, I pulled it out and found very little contamination, which I cleaned anyways. Made no difference. Here's one more clue. The sticking only happens when I'm moving. When I'm sitting still, truck running, there is no throttle hesitation at all, not one little bit. As soon as I'm moving, if I let off the throttle completely, I have to tromp on it to get past the resistance. Most puzzling. Link to comment Share on other sites More sharing options...
carnuck Posted November 15, 2011 Share Posted November 15, 2011 Someone suggested the throttle cable fraying near the end. I've seen that before. Can you move the throttle under the hood easily or? If automatic, could the neutral shift cable from the column be causing an issue? The throttle plate may be loose or needing adjusting. Link to comment Share on other sites More sharing options...
flint54 Posted November 15, 2011 Author Share Posted November 15, 2011 Carnuck thanks for your input but did you read both of my descriptions? The part that says everything moves freely? Motor off, and motor running but not moving? My sig that says AX15? Link to comment Share on other sites More sharing options...
carnuck Posted November 17, 2011 Share Posted November 17, 2011 Does it get hard to move when you turn the key on but not running? (missed the AX-15 part. Text size wasn't readable on my screen at the time and the color blended in with the black background) Link to comment Share on other sites More sharing options...
flint54 Posted November 18, 2011 Author Share Posted November 18, 2011 Nope. Let me recap: truck off - throttle moves freely ignition on (not running) - throttle moves freely motor running (but parked) - throttle moves freely driving (<10 mph) - throttle moves freely driving (>20 mph) - throttle sticks badly IAC and TB are very clean. Throttle plate is tight, centered, smooth edges, and pristine. TB is nearly new, and no marks on the bore that would suggest any hangup or sticking due to fit. Cruise cable is disconnected. This all began less than 300 miles ago, midway through a trip. Nothing was altered. I cannot convince myself that manifold vacuum is a factor, but nothing else makes sense either. Vacuum reading is steady 20 in. at idle. Pop the throttle and vacuum spikes low, spikes high, then returns to steady 20 in., exactly as it should. Link to comment Share on other sites More sharing options...
carnuck Posted November 19, 2011 Share Posted November 19, 2011 Sounds like the screws that hold the throttle plate are loose Link to comment Share on other sites More sharing options...
flint54 Posted November 19, 2011 Author Share Posted November 19, 2011 Carnuck you're shooting from the hip, and not paying attention to what I write. From most recent post: Throttle plate is tight, centered, smooth edges, and pristine. TB is nearly new, and no marks on the bore that would suggest any hangup or sticking due to fit Even if they were loose, which they are not, why do you think that would only be an issue when moving? Link to comment Share on other sites More sharing options...
HOrnbrod Posted November 19, 2011 Share Posted November 19, 2011 That's carnuck's modus operandi. :yes: Have you checked for any fault codes using the key? Worth a shot............. Link to comment Share on other sites More sharing options...
carnuck Posted November 19, 2011 Share Posted November 19, 2011 If tehre was play in the throttle plate screws and bushings, the suction could pull it enough to catch on an edge that it wouldn't without vacuum. Missed the other stuff :ack: I'd try another throttlebody since nothing else seems to be causing it. 20 inches of vacuum is higher than most motors when not coasting though. Link to comment Share on other sites More sharing options...
flint54 Posted November 20, 2011 Author Share Posted November 20, 2011 To check that box, I tested fault codes and got only "55" (end of codes). Tomorrow I'm going to install a NOS IAC I scored, just to rule out a sticking plunger, even though there's no mechanical relationship between throttle and IAC. If money was no concern, my solution might include one of these: http://www.4x4community.com/forum/showt ... hp?t=30945 Sometimes I really do miss carburetors......... 20 inches vacuum seems like an indicator of really good motor health, probably higher than many, but not excessively so. Link to comment Share on other sites More sharing options...
HOrnbrod Posted November 20, 2011 Share Posted November 20, 2011 If money was no concern, mysolution might include one of these: http://www.4x4community.com/forum/showt ... hp?t=30945 This kit never made it to market, and Rimmer Engineering is now belly-up. Hesco has one though. :D Link to comment Share on other sites More sharing options...
cruiser54 Posted November 20, 2011 Share Posted November 20, 2011 Here's a thought. I'm way more up to speed on Renix but I'll throw this out there. Does your TB have a screw to stop the butterfly? I'm wondering if the butterfly is closing too far into the bore of the TB and this is being exagerated when manifold vacuum is present. Perhaps backing the screw out, then tightening it in just until the butterfly begins to move open would be a good idea. Link to comment Share on other sites More sharing options...
flint54 Posted November 20, 2011 Author Share Posted November 20, 2011 Cruiser, you might get the prize! That is something that also came to mind as a possible solution. My 62mm TB does have such a screw (at the linkage) and I could easily try this, while watching the RPM so as to not raise the idle too much. As you say, it would reduce the possibility of close-fitting butterfly compounded with high manifold vacuum being the cause of this issue. I will post the results tonight. Link to comment Share on other sites More sharing options...
flint54 Posted November 20, 2011 Author Share Posted November 20, 2011 "Hesco has one though. :D" Sure enough they do! My guess is, the only reason you do not yet have one, is because they do not offer one that's chromed? :rotfl2: Link to comment Share on other sites More sharing options...
flint54 Posted November 20, 2011 Author Share Posted November 20, 2011 Crusier gets the prize! Crusier, I don't know what town you live in, but if I'm ever there I will buy you a pitcher of the beverage of your choosing. :cheers: :bowdown: Installed a new IAC, no change. Pulled the cable and soaked it with lubricant, no change. Pulled the TB and turned the setscrew (cannot reach with TB installed) no more than 1/4 turn, and voila!! No increase in idle speed, and throttle response EXACTLY as it should be, regardless of speed. Yaa Hoo !! Link to comment Share on other sites More sharing options...
HOrnbrod Posted November 21, 2011 Share Posted November 21, 2011 Where exactly is this screw? Does it contact the throttle body butterfly? Pic? Link to comment Share on other sites More sharing options...
flint54 Posted November 21, 2011 Author Share Posted November 21, 2011 Don, The screw is at the forward outboard corner of the TB mounting flange. It rises vertically through the flange and contacts the throttle link. You can see it in this image. It takes a 3/32" allen wrench from below. Probably a special tool to reach this with TB installed, but quick to pull TB and adjust. Tom Link to comment Share on other sites More sharing options...
HOrnbrod Posted November 21, 2011 Share Posted November 21, 2011 Thanks. :thumbsup: Link to comment Share on other sites More sharing options...
cruiser54 Posted November 21, 2011 Share Posted November 21, 2011 Crusier gets the prize! Crusier, I don't know what town you live in, but if I'm ever there I will buy you a pitcher of the beverage of your choosing. Prescott, Arizona and we have our own brewery!! LOL Link to comment Share on other sites More sharing options...
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