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I have a 1993 chevy blazer with a 5.7 v8, I’ve had it for 3 years and I did it’s first tune up, it was running fine, there were no issues that lead me to do the tune up, I just wanted to upgrade my compnents. I installed a mallory coil,mallory cap and rotor, mallory plug wires and AC plugs gaped at 0.035. The old parts showed normal wear, the plugs were all burning clean, they were autolite plugs, the only issue with them were they were gaped at 0.050, the under hood sticker said gap is 0.035, and that is what I gaped the new ones at. After the tune up the engine began having a small surge at idle, and also at idle when in gear, say at a stop light. When in gear at a stop, about every 15 seconds or so the engine changes idle speed “surges” for a couple seconds, and returns to normal.It runs great at every other speed,I wonder why the old plugs were gaped at 0.050? Do you think me gaping the new plugs at >0.035 caused the surge? I don’t see how but who knows.
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I never heard of plug gap doing that. I’d check around to see if, while stringing the plug wires, you maybe dislodged a vacuum hose or something.
If you don’t fling anything based on wyestech and barnyb’s advise, I would go back with AC Delco OEM plugs that the vehicle calls for. I learned this the hard way on a GM. I put in some high dollar Bosch plugs and all kinds of crazy stuff happened. The engine ran horribly. After replacing the new Bosch plugs with the AC Delcos it ran like a sewing machine. This may not be the issue, but it’s where I would start. The same is true with a Honda or Toyota. They call for NKG or Nippondenso. Best of luck to you
Because this started after you did the tune up I would recheck all of your work. Maybe you cracked a plug or a wire is arking. Look at how you routed the wires maybe one is too close to the exhaust manifold. Sometimes just to make sure I will run an engine in the dark with the hood open. Because you changed the cap and wire recheck the firing order, make sure you got the wires back in the right places. I’ve done that a few times in my life. Look at the cap and make sure you didn’t crack it. Worse case change everything back one part at a time I would think the culprit would show up in that process. Of course consider what the other guys have suggested.
I installed a 1 inch spacer under the throttle,body and while I had it off I removed the EGR valve and cleaned it and put a new gasket on. Afterwards the surging stopped. Must have been a vacume leak at egr or throttle body gasket.
Congrats on the find and fix….I know you’re glad thus was relatively easy. Hope she runs better than ever…
yup, I have a 93 yukon, which is basically the same as yours. I had the same surge at idle at stop signs and whatnot too. Replace my EGR valve and works great. Maybe it was bumped or something when you did your other repairs. Say, I was wondering how that intake spacer plate is working out for you. I’ve been told about improved gas mileage and all that. I think that just one or two cables or something had to be adjusted to get everything to normal? is that right? mileage go up?
The idea with the spacer is that less heat is transfer to throttle body/injector.
They also suspect better torque overall as you have a longer plenum piping but I really doubt that. You would need to compare that science with old oval racing that were tuning the intake tube the same way as the exhaust tube.
You would need some serious mods to see benefit in those and at that moment the throttle body size would be a restriction in itself.
But if you live somewhere relatively hot. Having a cooler throttle body would definitly reveal more power that would be there in cooler area
Glad you found the issue. It did sound like a vacuum leak. More info here if you run into something like that in the future.
http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
Thanks for the update and for using the ETCG forum.
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