Surging Idle: Thinking out loud
- Thread starter wczimmerman
- Start date
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wczimmerman
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- William
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- 1987
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- V2500
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- 5.7L
Yes: I forgot to mention that. The EST (advance) wire was unplugged and I put new plugs, cap, rotor, air filter, and oil in at the time, too.
notime2d8
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Well, you're running out of parts to replace here. Is the distributor new? If not you may have a 30yr old pickup coil in it. When i had this issue on my elcamino i replaced the factory distributor with a new one from ebay for $54. It fixed all of my issues as the old one was rusty and corroded and barely picked up.
On my K5 i had the same issues but i did the cheap distributor from ebay, IAC valve, checked for vacuum leaks....replaced the timing chain. My timing chain was stretched a good bit.
Sorry for the long post. But i had that exact issue on my El Camino and it was my distributor.
wczimmerman
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Well, this is embarrassing...
Apparently, my new "advanced timing light" was too advanced for me! I wasn't turning on the timing light correctly which resulted in the erratic reading for the timing. Once I figured out the right setting, it worked great.
The timing was about 1-2* and steady. I tried moving it to 8* BTDC but it was pinging badly so I moved it backwards and ended up on the first "point" below 0*. Since the truck would ping intermittently at 1-2* I thought I would try the opposite and see what difference that would make. Well, the truck runs great now! It doesn't ping at all and it, so far, it isn't surging on idle.
Maybe the timing marks are off?
To answer the question about the distributor: it was replaced with a brand new unit with the new engine.
Apparently, my new "advanced timing light" was too advanced for me! I wasn't turning on the timing light correctly which resulted in the erratic reading for the timing. Once I figured out the right setting, it worked great.
The timing was about 1-2* and steady. I tried moving it to 8* BTDC but it was pinging badly so I moved it backwards and ended up on the first "point" below 0*. Since the truck would ping intermittently at 1-2* I thought I would try the opposite and see what difference that would make. Well, the truck runs great now! It doesn't ping at all and it, so far, it isn't surging on idle.
Maybe the timing marks are off?
To answer the question about the distributor: it was replaced with a brand new unit with the new engine.
wczimmerman
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- 5.7L
Drove the truck into work this morning and while the pinging is gone, the surging is still present, though significantly reduced and the pulses are longer in duration. In other words, the frequency of the up and down of the idle is less and the amplitude of the RPM change is less. The tune up and timing change seemed to have helped but not solve the issue.
1987 GMC Jimmy
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This truck just doesn't wanna get fixed. Did you EFE explore the MAP issue further. Here's a nice thread that forum member George wrote up. I went ahead and did the live scan tool, and it's a great thing to have. Every TBI/TPI owner should be required to have one. You could try this and see if you find anything. Did you ever further explore the MAP sensor stuff?
wczimmerman
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- 1987
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- 5.7L
I have not taken a dive into the MAP question you mentioned yet. I have had a list of things that are part of the normal maintenance that I have to tackle first, time and weather permitting (no garage). The tune up, etc were on that list. I have an ACDelco O2 sensor coming to replace the Bosch that has over 30K miles on it (maintenance guidelines say replace every 30K). Yesterday I plugged the EGR valve line at the solenoid as a test. This morning's drive had no surging idle. Maybe I have an EGR removal plate as my next project...we'll see. I'm waiting until the O2 sensor comes and I get it installed before moving to the next thing.
The truck isn't running bad but I'm not crazy about the timing being retarded currently. I'd like to at least get back to 0* and I'd be thrilled to get to 8* BTDC without pinging.
